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Optics 9

This weblog post is the ninth of a series of about optics and optical equipment. It is about hand lenses, stereo microscopes, compound microscopes and digital microscopes, in that order!

Buntzen Lake looking north from public beach at south end. Photo: Patleahy, 2007-05-28.

In my childhood, my father, Edgar, called Mac (1906 – 1991), would regularly take my sister and I for long walks out in the woods. A favourite location was Buntzen Lake. It is 4.8 km long occupying an area of 182 hectares. Located north of Port Moody about 24 km from our house in New Westminster. These walks were the main source of my continued enjoyment of nature.

We usually circumnavigated most of the lake. Today, after the construction of a suspension bridge, the usual walk is about 8 km long, with which would take 4 – 5 hours, and an elevation change of 100 m. Before the suspension bridge was built, a shorter walk around most the lake took about 3 hours, with limited elevation change, possibly 20 m. The lake has provided hydroelectric power since 1904.

Both of my parents were hunters and fishers. One of my mother, Jennie’s (1916 – 2021) only regrets, was her failure to buy a particular rifle when she had the opportunity. Yet, she travelled the world, visiting in excess of 100 countries. As a parent to an adopted child, I think she was somewhat surprised that I had so little interest in her pastimes. In my childhood I had an interest in birds from pigeons to loons to falcons.

In my early teenage years, I developed an interest in marine biology, especially plankton, but also marine invertebrates. Several books led me in this direction. One of the first was, Rachel Carson’s (1907 – 1964) The Edge of the Sea (1955). This was actually the third of her Sea trilogy, and looked at three edges: rocky, sandy and coral. The focus was on the east coast of North America. The rocky shores were typical of the Cape Ann region of Massachusetts, the sandy shores were of the intermediate coast off the Carolinas, while the corals were part of the Florida Keys.

I also wanted to read something related to the Pacific Coast, where I lived. This was found in Ed Ricketts’ (1896 – 1948) Between Pacific Tides (1939). I am sure I read a later edition than this. Currently, I own a copy of the 5th edition, from 1985.

The third work that inspired me was Ralph Buchsbalm’s (1907-2002) Animals Without Backbones (1938). Originally, I owned a Pelican edition in two volumes from 1957. My current reference copy is from 1987, in a single volume.

I acquired a compound microscope in 1962, for my 14th birthday, As explained in Optics 6, I used this with a camera to take photomicrographs of plankton and other organisms. In high school use of a compound microscope was part of the biology course. When, I studied biology at college, we were required to use hand lenses, stereo microscopes and compound microscopes, in that order.

An Opticron glass hand lens = inspection magnifier, with chrome plated metal protective cover, 10 × magnification, with a 23 mm diameter glass lens. There is space for the attachment of a thin lanyard. Photo: Opticron.

The college biology program I undertook emphasized field trips to various ecological areas, and in all seasons. In addition to other equipment such as skis, we were required to have a pocket lens = inspection magnifier with us that could magnify up to 10 ×, for field trips. The lens can be made of glass or plastic, with plastic being cheaper and lighter but of lower optical quality and more difficult to clean. I prefer glass lenses.

An element is an individual piece of glass within a lens. Hand lenses can be constructed with one (singlet), two (doublet) or three (triplet) lens elements. Each element is specially shaped to correct for a particular type of optical distortion so the more elements, the higher quality the image. A singlet is gudenuf.

A 10 × magnification hand lens is adequate for most purposes. Higher magnification lenses are harder to use. Large diameter lenses provide a wider field of view = they are easier to use but, but are more expensive. I have always used a hand lens 20 – 30 mm in diameter. The description of a hand lens often follows the same convention as binoculars, with lens magnification followed by the lens diameter in mm. Sometimes, the order is reversed.

Some people comment that the use of a hand lens can be challenging. People often start holding the lens close to their eye then a) move the subject closer to your eye (if the object is moveable) or b) move their head with the hand lens, closer to the subject until it comes into focus (is the object isn’t moveable).

Some lenses come with multiple LED-lights for effective illumination in weak light. Some are further optimized with UV lights, so that it is possible to see fluorescence, not just in plants, animals and minerals, but also postage stamps and paper currency.

A lanyard should be fitted to the hand lens. I use braided mason’s twine. It is durable and comes in a variety of bright colors. Mine comes packaged will three 80 m bunts, in red, blue and yellow. Braiding adds strength and reduces tangling. Bonded twine means that it is coated to make it stiffer and more resistant to wear and moisture. Blue is a useful colour, since it is not often found in nature. The lanyard should be put around the person’s neck, so that the lens won’t be lost.

Stereo Microscope

When we returned to our classroom from a field trip, we would re-examine specimens using a stereo microscope. My current Dutch BMS stereo microscope has 10 × eyepieces, with a 2 × and 4 × combined objective, giving a magnification of either 20 × or 40 ×.

This Galilean optical system used here is an arrangement of fixed-focus convex lenses is used to provide a fixed magnification, but with the crucial distinction that the same optical components in the same spacing will, if physically inverted, result in a different, though still fixed, magnification. This allows one set of lenses to provide two different magnifications. Yes, it is important to know what magnification one is using, so that sizes in the microscope can be converted into real world sizes.

In my student days, stereo microscopes were commonly used as an aid for dissection. The major problem with this microscope is that it is not designed to take photomicrographs.

A BMS stereo microscope, with 10 x eyepieces, and 2 x and 4 x objectives allowing 20 x and 40 x magnification, suitable for dissecting biological samples.

Modern stereo microscopes are often coated with anti-bacterial paint. It is thanks to Charles Wheatstone ( 1802 – 1875) that stereo microscopes have two eyepieces. He discovered stereopsis = the fundamentals of depth perception, in 1840, allowing people to see objects in three dimensions. Eyepieces are typically inclined 45º with at least one tube being adjustable ±5 diopter, so that users can adjust the microscope to their eyes once. There should be no need to use eyeglasses while viewing through a microscope. There is a focussing knob, sometimes two for coarse and fine adjustments.

Illumination in a stereo microscope is most often incident = reflected from the surface of an object, rather than diascopic = transmitted through an object. In the new millennium, LED lights have been used for both incident and transmitted illumination. LED lights have a life of about 50 k hours. Usually, they work from mains electricity, 230 and 110 V through a transformer. Many stereoscopes include a rechargeable battery, so they can work offline, for up to about ten hours, with three hour charging times. This means stereo microscopes can now be taken out into the field, something that was not possible in my student years. Today it is common withDouble Pole Double Throw (DPDT) switches offer full separation from the mains power. The claim is safety, but I think part of the reason is related to prevention of battery drain. Power cords are typically detachable, and can be fitted with a C13 connector to the microscope and an appropriate power socket connector. For the model shown in the photograph, length x width x height = 150 x 133 x 358 mm, mass = 2.3 kg

In addition to its uses in biology, I also use my stereo microscope to inspect soldering and to examine electronic circuits.

Compound Microscopes

The compound microscope shown above is a MAGUS Bio 240T, a biological microscope, mainly used for education. It is designed for work with transparent and translucent biological specimens using brightfield illumination. The microscope has a revolving nosepiece suitable for four plan achromatic objectives . The 3W LED illuminator, has an intelligent control system to remember and maintain a different light intensity for each objective. There is an LCD screen, which displays operating parameters. The operational life of the illuminator is 50 k hours = 30 work years = almost a lifetime of work! Color temperature can be changed within the range of 3000 to 7000 Kelvin.

Magnification is from 40 – 1000 ×. The trinocular head has a vertical tube for mounting a digital video camera. There are two eyepiece tubes, both equipped with diopter adjustment rings, The head revolves and can make a full rotation. There are 2 standard 10 × /20mm eyepieces, fitted with rubber eyecups.

The microscope is equipped with coarse (left side) and fine (right side) focusing knobs. The coarse focus lock knob is located on the left side. It is used for adjustment after switching objectives.

The specimen stage is equipped with a belt drive mechanism that gently moves the specimen along the stage. The specimen holder is mounted with two screws. If necessary, it can be removed.

An Abbe condenser is centered along the optical axis. It is fixed, preventing the condenser from being moved accidentally, an important consideration in an educational microscope. The condenser has a numerical aperture of 1.25. Markings indicate objective magnifications. The iris diaphragm is adjusted by a knob. This can be used to increase image contrast, improving specimen visibility.

Selected settings are displayed on the LCD screen. Using a pair of knobs, you can adjust the light, set the sleep mode, or set the auto-off time.

After installing the microscope on the work area, the power supply and power cord can be hidden. The side openings in the stand act as handles allowing the microscope to be carried. or moved around.

Infinity plan achromatic objectives: 4×/0.10; 10×/0.25; 40×/0.65 (spring-loaded); 100×/1.25 oil (spring-loaded); Eyepieces 2 each 10×/20mm with long eye relief; 2 each eyepiece eyecups; C-mount camera adapter; light filter; bottle of immersion oil; power adapter = transformer, and power cord; dust cover; user manual. Additional equipment: Digital camera; calibration slide; monitor. Size (LxWxH) 450 x 300 x650 mm; mass = 9.8 kg; Mass = 9.8 kg

Digital Microscopes

Is a digital microscope a real microscope? This is a question I regularly ask myself, with the prepared answer being no. Unfortunately, for my prejudiced view of the world, digital microscopes are becoming better. Yet, my mindset, formed in the 1950s, still has difficulties accepting these as anything more than a slightly different digital camera, inferior to an optical microscope. The good news is that my world view is slowly changing. I have avoided purchasing a new compound microscope, in the hope that a digital microscope will make that investment unnecessary.

Part of the reason for my initial skepticism was that the first digital microscope I met was being sold as a toy. It was low-powered with a plastic lenses, and used a USB interface to connect to a computer monitor. It was incapable of working like a real compound microscope. A real digital microscope has to be more than a webcam attached to a macro lens.

An acceptable digital microscope should be computer controlled and automated, allowing advanced image analysis. At a minimum, it should be able to find/ calculate distance and area measurements. In a Wikipedia article about this topic, quantitation of a fluorescent or histological stain are mentioned.

What at one time was called USB 3.2, released in 2017, with two lanes of 10 Gbps simultaneously, with a maximum transfer rate of 20 Gbps over a USB-C connector. This is now called 3.2 Gen 2×2 = SuperSpeed USB 20 Gbps = USB 20 Gbps. Whatever its name, this allows a video resolution of up to 4k = 4096 × 2160 pixels, at a frequency of 60 Hz. Variable illumination should be provided with an LED source close to the camera lens. Modern, modestly priced digital microscopes offer magnification from about 20 × to 400 ×, sometimes more.

The real challenge with digital microscopes is obtaining software with device support. μManager provides professional microscopy software able to connect to a large number of devices. Some types of hardware are automatically supported, others not so much. μManager’s open device interface lets anyone write code to control microscope-related equipment, resulting a large and growing list of supported equipment. A scripting interface makes it possible to accomplish tasks that can not be executed within a graphical user interface (GUI).

The advantage of a digital microscope should not just be its low cost, and eyepiece elimination. It should also eliminate the mess and work of staining and preparing slides. With the use of sensitive photon-counting digital cameras, digital microscopy should be able to avoid damaging vulnerable biological samples.

The more advanced digital microscope units have stands that hold the microscope and allow it to be racked up and down, similarly to standard optical microscopes. Calibrated movement in all three dimensions are available through the use of a step motor and automated stage. The resolution, image quality, and dynamic range vary with price. Systems with a lower number of pixels have a higher frame rate (30fps to 100fps) and faster processing. The faster processing can be seen when using functions like HDR (high dynamic range). In addition to general-purpose microscopes, instruments specialized for specific applications are produced. These units can have a magnification range up to 0–10,000×, are either all-in-one systems (computer built-in) or connect to a desktop computer. They also differ from the cheaper USB microscopes in not only the quality of the image, but also in capability, and the quality of the system’s construction giving these types of systems a longer lifetime.

Conclusion. When people think of optical devices for biology, they think that they will get the most value for their money be acquiring a compound microscope. For me, the most value comes from a hand lens. After this, a stereo microscope is the most practical. It is only if one is interested in cellular biology that a compound microscope is needed. In my old age, I have lost interest in preparing slides, so that I can view samples with a compound microscope. Appropriate preparation takes time. Samples have to be cut very thinly. Most often they have to be stained, so that contrasting parts in a cell can be seen. When pressed for advice, buy a good quality hand lens. Use it for a year before even considering anything else. Except for people with an interest in cellular biology, that something else should be a stereo microscope. Use it for at least a year before investing in a compound microscope.

This post was originally written on Friday 2024-03-22 as Optics 2. It was saved, for the first time at 18:10. On 2024-04-09 at 20:06 it was scheduled to be published on 2024-06-29 as Optics 6. Later on 2024-04-25, it was rescheduled for 2024-07-06 at 12:00. On 2024-04-27, it was it was reconstituted as Optics 9, and rescheduled for 2025-01-25

On 2025-03-01, Optics 10 will be published. It is about digital cameras. On 2025-03-08, Optics 11 will be published. It is about photographic collections.

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Optics 8

This is a Celestron Nexstar 8SE, often described as a good telescope for beginners/ hobbyists. It is the biggest telescope in Celestron’s iconic orange tube family. Its optics are acceptable, and it gathers lots of light. It is even affordable, at about US$ 1 000. Despite this, I am unconvinced this is a telescope for me. There is too much automation, hiding its operations. I want to know what is happening. Photo: Celestron.

This weblog post is the eighth of a series about optics and optical equipment. Optics 8 is about astronomical telescopes. Optics 9 is about microscopes. Later in 2025, two additional posts will appear: #10 is about digital cameras; #11 is about digital photograph collections.

Scandinavian winters are long and dark. Every year, in January, I go through a period where I considered acquiring a telescope. So far, I have not done so. In large part, it has to do with the reality of cloud cover. Norway is one of the most extreme places in the world for cloud cover. That said, Trøndelag is better than most places in Norway.

There has only been one type of telescope I have ever consider buying: a Celestron 8.

Before discussing it, and other telescopes suitable for amateurs, there is the history of astronomy to endure.

Johannes Kepler (1571–1630) investigated some of the laws of optics in his lunar essay (1600). In 1603, Kepler focused on optical theory, published as Astronomiae Pars Optica = The Optical Part of Astronomy (1604). It described the inverse-square law governing the intensity of light, reflection by flat and curved mirrors, principles of pinhole cameras, the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies. This work provides a foundation for modern optics, despite the absence of anything about refraction.

In physics, refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction.

Willebrord Snellius (1580–1626) developed the mathematical law of refraction = Snell’s law, in 1621. René Descartes (1596–1650) used geometric construction and the law of refraction = Descartes’ law, to show that the angular radius of a rainbow is 42°. He developed the law of reflection, Dioptrique (1637, French) = Optics = Dioptrics (both English) a short treatise that was the first published to mention this law.

Christiaan Huygens (1629–1695) wrote several works about optics. These included Opera reliqua and Traité de la Lumière (1690) which presents a wave theory of light. This theory was initially rejected in favour of Newton’s corpuscular theory of light, until Augustin-Jean Fresnel (1788 – 1827) adapted Huygens’s principle to give a complete explanation of the rectilinear propagation and diffraction effects of light in 1821. This principle is now known as the Huygens–Fresnel principle.

Isaac Newton (1643–1727) investigated the refraction of light, demonstrating that a prism could decompose white light into a spectrum of colours, and that a lens and a second prism could recompose the multicoloured spectrum into white light. He also showed that the coloured light does not change its properties by separating out a coloured beam and shining it on various objects. Newton noted that regardless of whether it was reflected or scattered or transmitted, it stayed the same colour. Thus, he observed that colour is the result of objects interacting with already-coloured light rather than objects generating the colour themselves. This is known as Newton’s theory of colour. From this work he concluded that any refracting telescope would suffer from the dispersion of light into colours, and invented a reflecting telescope (today known as a Newtonian telescope) to bypass that problem. By grinding his own mirrors, using Newton’s rings to judge the quality of the optics for his telescopes, he was able to produce a superior instrument to the refracting telescope, due primarily to the wider diameter of the mirror.

In 1671 the Royal Society asked for a demonstration of his reflecting telescope. Their interest encouraged him to publish his notes On Colour, which he later expanded into Opticks. Newton argued that light is composed of particles or corpuscles and were refracted by accelerating toward the denser medium, but he had to associate them with waves to explain the diffraction of light (Opticks Bk. II, Props. XII-L). Later physicists instead favoured a purely wavelike explanation of light to account for diffraction. Today’s quantum mechanics, photons and the idea of wave-particle duality bear only a minor resemblance to Newton’s understanding of light.

In his Hypothesis of Light (1675), Newton posited the existence of the ether to transmit forces between particles. In 1704, Newton published Opticks, in which he expounded his corpuscular theory of light. He considered light to be made up of extremely subtle corpuscles, that ordinary matter was made of grosser corpuscles and speculated that through a kind of alchemical transmutation “Are not gross Bodies and Light convertible into one another, …and may not Bodies receive much of their Activity from the Particles of Light which enter their Composition?”

A Telescope

Selecting the right equipment is vital in amateur astronomy. Optical quality is the most important characteristic of any telescope because it contributes significantly to the clarity of celestial bodies.

The three most commonly used types of telescopes:

1. Refractors: These use glass lenses at the front of the tube, a design often favoured for planetary observations.

2. Reflectors: These use mirrors instead of lenses. These are preferred for observing deep sky objects such as faint galaxies and nebulae.

3. Compound/ catadioptric: These combine lenses and mirrors. They are versatile, and can be used for viewing a variety of celestial objects.

The Tracking Platform

A telescope tracking platform can be built to allow a telescope to move in sync with the rotation of the Earth: to track stars, planets and other celestial objects as they move across the sky. While mechanical components provided timing, increasingly computers provide this today. Part of my interest in tracking involves the Forth programming language.

Everything in the night sky is in constant motion. This is mainly due to Earth’s rotation. Without a tracking system, a telescope, regardless of its quality, will only provide fleeting views. Tracking systems help a telescope to consistently follow celestial bodies, by moving the telescope at a similar rate and direction, mimicking the sky’s movement. This is especially important for astrophotography, that could require long exposure times.

Building a telescope tracking platform requires diligence, patience and persistence. Platforms can be complex and require fine-tuning and troubleshooting. Telescope tracking platforms come in two basic types:

Alt-Az Mounts: They move up-and-down (altitude) and side-to-side (azimuth). These mounts are often easy to use, making them suitable for beginners, for general observation and short-term tracking. They are not suitable for long-term tracking or astrophotography.

Equatorial Mounts: These mounts rotate along an axis parallel to Earth’s rotation. They require alignment with the Polaris = North Star. Equatorial mounts offer superior tracking for longer periods and are needed for astrophotography.

A mount alone doesn’t make a perfect tracking system. Location, local climate, the telescope’s size and weight have to be taken into consideration, along with motor drives and functionality.

Designing a telescope tracking platform is dependent on location. This impacts the effectiveness of a tracking system. A northern hemisphere, polar alignment will be different from that in the southern hemisphere. The altitude and azimuth of the celestial pole vary with latitude and longitude.

Humidity and temperature influence the telescope’s operation. In extreme cold, the lubricants in the mounts may thicken, hampering smooth movements. High humidity can lead to rusting of the metal parts.

The size and weight of a telescope also affect mount choices. Heavier telescopes require sturdier mounts to support their weight.

Maximum weight capacity varies with the mount. A typical amateur alt-azimuth mount can have a mass of 20 kg, while for an equatorial mount this can be 50 kg. While a a casual stargazer, can co-exist with an alt-azimuth mount for general observation, someone actively engaged in astrophotography, will need an equatorial mount, because of its superior tracking capabilities.

While tracking mount components are widely available online, it is sensible to acquire all the necessary materials before starting to build a telescope tracking platform. This prevents surprises and unnecessary delays. The functionality of the platform directly depends on component quality.

Some crucial components include the mount. Metal bars are needed for the base and rocker. Here, durability is important, so consider stainless steel or aluminum. Quality ball bearings used in the pivot point, will ensure smooth rotation of the platform. Motor and Gears should be selected to enable auto-tracking, with an adjustable motor speed capable of matching the Earth’s rotation.

Minimum tool requirements, include a screwdriver set, drill, hacksaw, wrenches and a level.

Before building the telescope tracking platform create a detailed design on paper or using design software. This design should show the mount, metal bars, ball bearings, motor and gears.

Start assembling the components beginning with the mount. Because it forms the core support system for the tracking platform, it must be sturdy and well-balanced. Affix the metal bars to provide a frame that can withstand your telescope’s weight, ensuring better stability and tracking accuracy. Place ball bearings in strategic locations to allow smooth rotation of the platform. Connect gears appropriately to the motor, to ensure their rotation is synchronized with the tracking process.

Integrate a controller into the platform to governs the motor speed and direction. Most modern controllers come with a capability to store star maps and tracking speed presets to make tracking easier and more efficient. Once the platform build is completed, a regular maintenance schedule must be devised, and followed.

Once the telescope tracking platform is assembled, it is crucial to run initial tests to ensure everything functions as expected. Drift alignment aligns the telescope with the Earth’s axis of rotation. Point the telescope at a bright star near the celestial equator and monitor its movement. If everything is correctly assembled and calibrated, the star should stay stationary in your telescope’s field of view. If the star drifts, adjustments will be necessary.

Correct controller calibration is essential to align the telescope with celestial objects. Polar alignment aligns the telescope’s rotational axis with the North Star.

Mechanical issues often involve simple corrections. Ensure the metal bars are firmly in place, the ball bearings move freely, and the gears are properly interlocked. Listen for unusual noises when it is operating. This could indicate a component is not operating as it should.

Power supply issues can cause problems. This applies to both battery and mains power. Ensure the supplied voltage matches the motor’s requirement, and there are no power fluctuations.

The Celestron Nexstar 8SE (shown in the photograph at the beginning of this post) is one often suggested for amateurs. It has a fully automated GoTo Mount, allowing users to select an object they want to observe with a database of 40 000 + objects. At the push of a button, the telescope will automatically point to it. The telescope is compact and Portable. With its Schmidt-Cassegrain optics it has a 20 cm aperture with good light-gathering power allowing views of the moon, other planets and deep-sky objects.

The telescope comes with a built-in wedge to polar align the telescope. A camera adaptor will allow the connection of a mirrorless or digital single lens reflect (DSLR) camera, for astrophotography. Other accessories are available that extend capabilities.

Tom Johnson (1923 – 2012) was an American electronics engineer and astronomer who founded Celestron, a company which revolutionized the amateur astronomy. He served as a military radar technician during World War II. In 1955, he started Valor Electronics, which produced electronics for military and industrial use, in Gardena, near Los Angeles, in California.

Celestron was created as the Astro-Optical division of Valor in 1960. Johnson had been looking for a telescope which could be used by his two sons, but found no child-friendly models on the market at the time. While building a 6-inch reflector telescope in 1960, Johnson encountered a lens-grinding kit. After several days of hand grinding, he invented a machine that would grind the lens for him.

Soon, the company was attempting to build various models of Schmidt–Cassegrain telescopes. However, these proved difficult to mass-produce because they needed Schmidt corrector plates, a hard to manufacture aspheric lens. To solve this production problem, company engineers invented a new type of telescope, the Celestron 8 in 1970, that was compact, affordable and easy to manufacture.

Meanwhile, further north in Watsonville, California, Meade Instruments, founded by John Diebel (1943 – ) in 1972, started selling Japanese telescopes. It became the world’s largest manufacturer of telescopes, starting in 1976. Unfortunately, they used litigation as a means of preventing competition. They ceased operation in 2024, after losing some important lawsuits.

The largest telescope brand in the world is now Sky-Watcher, established in 1999 by the Synta Technology Corporation of Taiwan. It markets telescopes and astronomy equipment, such as mounts and eyepieces, aimed at the amateur astronomy market. The products are manufactured in Suzhou, China. The brand is primarily distributed in North America and Europe.

Buying a telescope is usually an easy and inexpensive way of acquiring an astronomical telescope. However, some people are more inclined to make rather than to buy. Amateur telescope makers (ATMs) build telescopes as a hobby, for personal enjoyment of a technical challenge. They will claim, often to a spouse, that they are saving money, but this is seldom more than an excuse. Sometimes it is done to provide custom features on a telescope, or for research purposes.

John Lowry Dobson (1915 – 2014) was an American amateur astronomer, best known for the Dobsonian (light bucket) telescope, a portable, low-cost Newtonian reflector telescope. He promoted awareness of astronomy through public lectures and sidewalk astronomy performances. His Dobsonian telescope is an alt-azimuth mounted Newtonian telescope design popularized in 1965. It vastly increasing the size of telescopes available to amateur astronomers. Features included a simple, easy to manufacture, mechanical design, using easily available components to create a large, portable, low-cost telescope. The design is optimized for observing faint deep-sky objects such as nebulae and galaxies, with a large objective diameter, short focal length. Their portability allowed travel to less light-polluted locations.

At some future date, I intend to construct a small astronomical observatory, with its own telescope. The major problem with Vangshylla is its lack of clear skies. The Climate Research Unit of the University of East Anglia calculated cloud cover between 1991–2020 in 196 sovereign countries and Greenland. Norway had 81.5% cloud cover. Algeria has the least at 21.0%. There are only two countries with more cloud cover than Norway: São Tomé and Príncipe with 83.5%, while Greenland has 83.7%. Finland, the United Kingdom and Sweden are close with 79.6, 78.4 and 78,2%, respectively.

The following applies to Steinkjer, ca. 35 km north east of Vangshylla. In Steinkjer, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year. The clearer part of the year in Steinkjer begins around 04-07 and lasts for 5.3 months, ending around 09-17. The clearest month of the year is May, during which on average the sky is clear, mostly clear, or partly cloudy 45% of the time. The cloudier part of the year begins around 09-17 and lasts for 6.7 months, ending around 04-07. The cloudiest month of the year is January, during which on average the sky is overcast or mostly cloudy 74% of the time.

Of Canada’s sunniest places = least cloud cover, ranks 9 to 18 (with one exception #13) are cities in British Columbia. These are: # 9 = Kelowna (where my mother grew up), # 10 = Kamloops (where Trish’s sister and other relatives live), # 11 = Penticton, # 12 = Vernon, # 14 = Prince George, # 15 = Abbotsford, #16 = Nanaimo (where my father grew up), # 17 = Chilliwack and # 18 = Victoria.

In my childhood, I visited the The Dominion Astrophysical Observatory, located on Observatory Hill, in Saanich, British Columbia, near Victoria. It was close to the experimental farm, also in Saanich, where my uncle was director. The main instrument is a 1.83 m Plaskett telescope. In its day, the observatory was a world-renowned facility where many discoveries about the Milky Way were made. It was one of the world’s main astrophysical research centres until the 1960s.

The Plaskett telescope was planned to be the largest telescope in the world, but delays caused by World War I, and production errors requiring two regrindings of its mirror, meant it was completed 1918-05-06, six months after the 2.54 m Hooker telescope at Mount Wilson Observatory, in Los Angeles, California.

Note: This post was cloned as Optics 5 from Optics 4 on 2024-03-23. It was saved, for the first time at 8:00. On 2024-04-09 at 20:09 it was scheduled to be published 2024-06-22 at 12:00. On 2024-04-27 it was reconstituted as Optics 8 and rescheduled to be published 2025-01-18 at 12:00. Later that date was changed to 2025-01-25.

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Optics 7

Originally, this photo was supposed to be one of Trish’s maternal grandmother’s opera glasses. Immediately before publication, they could not be found for a photo shoot. So this pair, appearing in Wikipedia were substituted. Early 20th century mother of pearl opera glasses & leather case. The glasses are marked with the name of the vendor “Ryrie Bros. Toronto” Photographer: Sobebunny, 2009-12-26.

This weblog post is the seventh of a series about optics and optical equipment. This post is about binoculars, but also includes opera glasses, monoculars and spotting scopes. Future posts: # 8 is about astronomical telescopes; and, #9 is about microscopes. Later in 2025, two additional posts will appear: #10 is about digital cameras; #11 is about digital photograph collections.

Binoculars specification values include information about strength (magnification power) and size (objective lens diameter). These are typically designated with two numbers, such as 8×40, where 8 is the magnification power while 40 is the diameter (in millimeters) of the objective lenses = the lenses closest to the object being viewed. Objective lens size tells: 1) how big physically the binoculars are, and 2) how much light they can gather. These numbers fail to provide information about the quality of the optics or other features such as: rubber protective covering, waterproofing and fog-proofing or – often importantly – type of prism and type of glass.

Binoculars provide users with a three-dimensional image because each eyepiece presents a slightly different image to each eye and this parallax = displacement = difference in the apparent position, allows a viewer’s visual cortex to generate an impression of depth. Monoculars are unable to achieve this.

Most early binoculars used Galilean optics = a convex objective and a concave eyepiece lens. It presented an erect image but with a narrow field of view and low magnification. This construction is still used in cheap models and opera glasses. Aprismatic binoculars with Keplerian optics = twin telescopes, provides each tube with relay lenses to erect the image. A relay lens is a lens or lens group that inverts an image and extends the optical tube. Relay lenses are found in refracting telescopes, endoscopes and periscopes to extend system length. This is done before the eyepieces, which is used to invert an image.

An endoscope = an inspection instrument composed of image sensor, optical lens, light source and mechanical device, which is used to look deep into the body by way of openings such as the mouth or anus. A periscope = an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer’s current position. In its simplest form, it consists of an outer case with mirrors at each end set parallel to each other at a 45° angle.

In optics, an erect image is one that appears right-side up. An image is formed when rays from a point on the original object meet again after passing through an optical system. The opposite of an erect image is an inverted image.

When lenses are part of a computing device, there is no need to transform images to form an erect image. This can be done efficiently by a graphics processor inside the device, before the image is shown on a screen.

Classification of binoculars and related optical instruments

Indoor vs outdoor: Opera glasses are designed to bring clarity to indoor/ theatrical experiences, while most of the other instruments, including binoculars, are designed to bring clarity to outdoor experiences.

Size of objective lenses: Binoculars are categorized into compact, midsize and full-size models, based on the size of their objective lenses. Variations in optics, design and construction can mean that models with the same size objective lenses will differ in bulk and weight. Some binoculars are bulky so that they will float.

Bulk: Lightweight compact models make sense for hiking. Midsize models with larger objectives, are bulkier, but provide brighter images and can be more comfortable to hold for long periods. Full-size binoculars can be useful in low-light conditions, but are heavier, and less comfortable, without a tripod.

In comparing lenses it is often useful to compare the area occupied by the objective lens, not its diameter. Thus, Area = π · r2 where π = 3.14 and r = 20 mm for a 40 mm diameter lens. This gives an area of 1256 mm2. but r = 40 mm for an 80 mm diameter lens, gives an area of 5024 mm2 which is 4 times as much.

In an article about binoculars for old people, it was suggested that consideration should be given to three features that younger people may be able to ignore. First, use light weight binoculars, substituting a roof prism, for a Porro prism; second, to maximize eye relief, buy binoculars that have an increased distance between the eye and the eyepiece to see the full image; third, decrease magnification from 10× to 8× or even 6×.

Prisms

Isaac Newton (1642 – 1727) used a prism is to disperse white light into component parts. Dispersion is of limited interest when it comes to using prisms in the real world. There is no perfect prism, but two have become standard in binoculars. The Porro prism is named after Italian Ignazio Porro (1801-1875) who invented it ca. 1850. The roof prism is a later invention.

Since the 1960s, handheld binoculars with roof prism-based reversing systems have become increasingly popular. Yet, these prisms are also problematic. Their use has led to a loss of image resolution, which turned out to be the consequence of unwanted interference: the total reflection occurring in the prisms causes a partial polarization of the beam. This beam is then split at the roof edge, with the two half-beams being reflected in different directions. After all the partial beams have been combined, however, their polarization vectors point in different directions, which corresponds to a phase shift and leads to a loss of resolution via the interference effects mentioned above. This phase shift occurs in perfectly manufactured prisms!

Binoculars with roof prisms are more compact and streamlined, lighter weight, and much easier to carry around than binoculars with Porro prisms. Roof prisms are more complex because there is no easy horizontal offset. Roof prisms take advantage of intricate and convoluted machined paths that reflect the light from the objective to ocular lenses. In 2025, people should choose roof prism binoculars, if they can afford it.

Usage:

Binoculars for backpacking and hiking should be small and light weight. Suitable models are often referred to as compact binoculars, with magnification of 8 or 10, and an objective lens diameter less than about 28 mm. Rubber coating, water resistant or waterproof will be appreciated.

Binoculars for wildlife viewing also include those used on safaris and for whale watching. They use a higher magnification (10 rather than 8) if one is likely to be located far away from the animals. Midsize (32mm) is preferred rather than full-size (42mm) if one wants something more compact. Water resistance is useful, but waterproof models are preferred for whale watching (or any other watching) from a boat.

Birding is a sub-genre of wildlife watching. Many birders are less concerned about size and weight, preferring midsize or full-size models such as 8×32 or 8×42. A 10-power magnification will have a narrower field of view compared to an 8 power pair. A wide field of view is useful for locating birds, and other wildlife that is moving. Water resistance is also a good feature, as are those that limit fogging when they go from a warm vehicle to cooler outside environments.

Binoculars on boats should have a low magnification (8 or less) because boat movements can make steady viewing challenging. Waterproof models are useful. 8×32 is a popular size.

For stargazing, one should maximize magnification and light gathering capabilities by choosing full-size binoculars: preferably, 10×50. With higher magnification, a tripod will be necessary. Telescopes for astronomy will be discussed in Optics 8.

Opera glasses = theater binoculars = Galilean binoculars, are compact, low-power optical magnification devices, usually used at indoor performances. Magnification power below 5× is usually desired to minimize image shake and maintain a large enough field of view. A magnification of 3× is preferred. The design of many modern opera glasses of the ornamental variety is based on the popular lorgnettes of the 19th century. Often, modern variants are equipped with an LED flashlight, allegedly to help people find their place in the dark.

Binoculars at Cliff Cottage

Our oldest optics are opera glasses previously owned by Trish’s maternal grandmother, made by (or at least labeled by) G. E. Trorey, in Vancouver. The Trorey jewellry company was started in 1893, and is famous for building what later was called the Birks clock. It was made to celebrate Trorey’s fifth anniversary. Birks bought Trorey in 1906. So, these opera glasses date from before then.

In the early 1980s we purchased a pair of Tento BPC 7 x 50 binoculars, in Molde, Norway. Tento = Technointorg = the Russian Ministry/ Office of Foreign Trade selling Russian optics outside the Soviet Union. БПЦ = BCP = бинокли призменные с центральной фокусировкой = binokli prizmienne s centralnoj fokusirowkoj = binoculars with central focusing. These were most likely made by Загорский оптико-механический завод = ZOMZ = Zagorsk Optical-Mechanical Plant, in Sergiyew Posad, 70 km north-east of Moscow.

On 2024-04-18, we decided that we needed better optical equipment. Yes, age may have been part of that decision. Since we have a optician in Inderøy, we decided to patronize them and buy a Breitler Ultima 10 x 42 binoculars. Specifications are provided below:

Brand/ model:Breitler Ultima
Objective diameter (mm):42
Magnification (x):10
Field of view at 1000m (m):101
Near limit focus (m):2
Exit pupil:4.2 mm
GlassBak-4
Prism typeroof
Features:Waterproof, Nitrogen filled , Protective covering
Product type:Binoculars
Diameter front lense (mm):42
Dimensions (L x W x H, mm)147 × 129 × 63
Mass: (g)670

Monocular vs Spotting Scope

Monocular scopes share most features with spotting scopes, but in a smaller size and with less power and capabilities. For instance: Head: It provides support for the eye piece and connects it to the objective lens. Nose piece: A rotatable component that holds and selects the active objective lens. Eye piece = ocular lens = the lens nearest to the eye which you look through to observe objects. Objective lens: They are usually 2 or 3 lenses, with a prism in the middle that folds the optical path and extends the entire optical system length for an erect image. Arm: supports the head and connects it to the base. Focusing ring: is located around the body in some monocular scopes. Some use a focusing lever or slider button instead. Zoom is optional on monocular scopes. Those that have them have a magnification that varies from 4× to 12×, with 8× considered standard.

Most spotting scopes allow the user to alternate between fixed length and zoom magnification. Zooming allows users to find objects at low magnification, and then to narrow the field of view and magnify the object to observe the details. A variation from 20× to 60× is common.

Spotting scope characteristics. Eye cup: A small and twist-up shield for the eye. Eye cap: A flexible rubber shield that protects a user’s peripheral vision against light, wind and dust, prevents glare caused by ambient light on the ocular lens, and limits distractions. It is also known as eye shield. You can extend or contract it to use it with glasses, or without. Ocular and objective lens caps: These are rubber coverings that protect the lenses from damage from water, dirt and impact during transit or in storage. Some of them can be flipped up. Focusing ring: You twist it to the right or left to adjust the focus for a clear picture. Some models have focus knobs instead of focus rings. You will also find dual focus spotting scopes with coarse and fine adjustments.

My formal training as a biology teacher began when I was over fifty. The emphasis was on observation in the field, which included instructions as to how to use a spotting scope for the observation of wildlife, particularly birds. Since a spotting scope comes with large objective lens and higher magnification, a fold-able tripod is needed to mount it on for support and to lessen the scope’s vibrations for steady viewing. In addition, they often have a lens hood = lens shade, to minimize objective lens glare in sunny conditions. These should be retracted in dim environments.

We have a Breitler Pant(h)er 20-60×60 45 degree spotting scope. It was a demo being sold for less than half price. Since we have an unloved tripod, that is no longer being used to hold a camera, it is being used as a support device for the spotting scope. Specifications are provided below:

Brand/ model:Breitler Pant(h)er
Objective diameter (mm):60
Magnification (x):20-60
Field of view at 1000m (m)/ :31.6-16/
Near limit focus (m):6
Exit pupil:3 – 1 mm
GlassBaK-4
Prism typeunknown
Features:Waterproof, Nitrogen filled , Protective covering
Product type:Spotting scope
Diameter front lense (mm):60
Dimensions (L x W x H, mm)340 x 90 x 165
Mass (g):873

Summary

People considering buying a new pair of binoculars may want to consider a spotting scope as an alternative, it is better for some activities, such as viewing wildlife from land. In terms of binoculars, a Porro prism with Bak-7 glass may be preferred if expense is an issue. These will be cheaper. In addition they offer greater clarity and a wider field of view. Most often they will be heavier, and not as durable. Binoculars with roof prism and Bak-4 glass will be more expensive, but offer: more durability, lighter weight, more compact dimensions, superior waterproofing, greater magnification strength, but they will have less clarity and a narrower field of view.

This post was originally written early in the morning of Monday 2024-03-18, under the title Magnification, that was later in the day changed to Optics 3. Saved, for the first time at 18:10. On 2024-04-09 at 20:08 it was scheduled to be published 2024-06-15 at 12:00. On 2024-06-27 it was changed to Optics 7 and rescheduled to be published on 2025-01-11 at 12:00. Somewhat later it was rescheduled to 2025-01-18. Additional content was added during the week immediately before publication.

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Optics 6

A Kodak Petit camera, identical to the first camera I used.

Since the first set of 5 weblog posts was published about optics, I have made some changes about upcoming post content. This weblog post is the sixth in a series. It is about analogue cameras; Future posts : #7 is about binoculars, but also includes opera glasses, monoculars and spotting scopes, scheduled for publishing 2025-01-18; # 8 is about astronomical telescopes, scheduled for publishing 2025-01-25; #9 is about microscopes, scheduled for publishing 2025-02-01. Later, two additional posts will appear: #10 is about digital cameras, scheduled for publication on 2025-03-01.; #11 is about digital photograph collections, scheduled for publication on 2025-03-08.

As I started preparing to write this post, my mind was comparing analogue photography with riding a horse. Something obsolete. However, I then began to remember that much of my photographic career was dependent on using specific types of cameras for very specific purposes. So yes, this is about analogue = film cameras.

My main objection to film cameras is the expense of film purchase and processing. In contrast to the camera that comes with almost every handheld digital device = smartphone, the marginal cost of taking an image is almost zero. Admittedly, those images have to stored somewhere, hopefully in multiple places.

Reminder: The 3-2-1 rule/ data protection strategy = save three copies of data, stored on two different types of media, with one copy kept off-site. This is very expensive to do with analogue photographs, especially if the negatives are missing. Flatbed and slide scanners can create digital copies inexpensively.

In general, a high quality colour image of 2 400 x 4 000 pixels can be reduced in size, without reducing quality, to occupy less than 1 MB, A 10 TB hard disk costs NOK 3 500 or less, and can store 10 million of these images at a cost of about NOK 0.00035/ image. That is about 1/300 of a cent/ image. Yes, one should keep three copies for backup purposes, which raises the cost to 1/100 of a cent.

Film

Unprocessed film is a perishable product that can be damaged by high humidity and high temperature. Fresh film is better able to provide true colour. Film should remain unopened in its original canister or plastic wrap. To protect against humidity, include a silica gel desiccant bag in the film storage container. Reuse of desiccant bags is possible.

Yet, because of a digital revolution, it was not always possible to buy film, so people attempted to preserve the film they had available. The situation in 2025, is much improved compared to 2005. In much the same way that some people prefer to listen to antiquated LP records played on turntables, some people like to revert to antiquated film technology.

Film that is expected to be used in less than 6 months, could be stored in a refrigerator at 8°C or lower. For longer term storage, years rather than months, a freezer can be used at -18°C or lower. Before use, film stored in a freezer, should be placed in a refrigerator for 24 hours. Film removed from a refrigerator, should be given 2 hours or more to adjust to room temperature. At one time, even after I had gone over to digital cameras, I had stored rolls of 35 mm Fuji slide film in our refrigerator, just in case. Currently, our refrigerator hosts one undated roll of Illford Pan F film.

Film available in 2025

Here are some notable films being manufactured

ADOX 20, a black and white film with ISO 20. “No other film is sharper, no other film is more finegrained, no other film resolves more lines per mm (up to 800 L /mm).”

Fuji one of only two remaining major manufacturers of colour film. The film range currently comprises: Consumer films = FujiColor/ FujiColor Superia and Professional films = Neopan, Velvia and Provia. Instax is a range of instant films and cameras launched in 1998 which now outsell the traditional products.

Kodak was established in 1888 and is the other major manufacturer still producing colour film. While these are manufactured in Rochester, New York, since its bankruptcy in 2012, distribution and marketing is controlled by Kodak Alaris, a UK based company, acquired in 2024 by Kingswood capital management. The film range is divided into Consumer films = ColorPlus & Gold/Ultramax, and Professional films = Tri-X, T-MAX, Ektar, Portra & Ektachrome.

Background

Analogue cameras are dependent on using light to create an image on film. Film is used as a generic term, because sometimes a film emulsion is placed on glass plates, or even a piece of metal. At Vangshylla, one of the local farmers has a hobby of using a 4″ x 5″ camera, with glass plates to produce images. I have assisted him once, to take a photo of his family, with him in it.

Personally, I have no intention of reverting to analogue photography again, even if I have stored the equipment needed to develop film in our attic. These items are historical objects to show people how humanity has progressed, technically.

Twentieth century photographic techniques

Photography uses a lens to capture a lighted image on a photographic plate in a camera. It is analogous to images passing through the lens of an eye, to create an image on the retina. In much the same way that it can be advantageous to live in a lighted room, sometimes additional light is needed to create a suitable photograph. A common approach is to attach an electronic flash. An important characteristic of photographic film is its light sensitivity, revealed in its ISO number. The actual amount of light hitting a photographic plate is determined by the shutter speed and the aperture opening. Both of these can be adjusted on most advanced modernish analogue cameras.

Shutter speeds are expressed as fractions of a second, a higher shutter speeds means a faster shutter speed, a shorter period of time that an aperture is open. Typical values are shown in the image below, typically starting with 1/1 000 and ending with 1/2 s. Most films did not produce normal results if the film speed is longer than 1/15 s. Speeds of 1 s or more are often referred to as time exposures. Shutter speeds of a longer duration, introduce blur in objects that are in motion.

Aperture openings are also stated numerically. The smaller the number the bigger the opening. Therefore, an f/1.4 is a very large opening while f/22 is a very small opening. A small opening is necessary to provide focus at depth. Large openings have a very limited focal depth.

Some people like to describe exposure in terms of a bucket being filled with water. The aperture is analogous to an adjustable hole that opens and closes at the top. The duration of the hole remaining open is analogous to a continuous stream of water entering the bucket. The smaller the hole at the top, the longer the hole would need to be open to fill the bucket with water. Conversely, a larger hole will need a shorter amount of time to fill the bucket. So in this analogy the water pouring in represents light. A full bucket of water is a properly exposed image.

Film speed is the measure of a photographic film’s sensitivity to light. The ISO, referring to the International Organization for Standardization, system was introduced in 1974. It combined a linear ASA = American Standards Association, scale used in the United States, with a logarithmic DIN standard 4512 by the Deutsches Institut für Normung used in Europe. Almost since its introduction, the DIN component has often been dropped.

The ISO arithmetic scale means that a film with an ASA 200 rating needs only half the light of a film with an ASA 100 rating. However, film with a higher rating, produce images with more grain.

Both the ASA and DIN systems have a long history, and many revisions. DIN goes back to at least 1934, but with links to The Scheinergrade system devised by the German astronomer Julius Scheiner (1858–1913) in 1894. It uses a logarithmic scale. My direct experience of ASA starts with PH2.5-1960, but versions of it date back to 1943.

Daniel Peter of Fotoblog Hamburg created this free downloadable cheat sheet card for photographers providing a basic overview of aperture, ISO values and shutter speeds.

The camera I remember best from my youth, shown at the beginning of this post, was my mother’s Kodak Petite, made between 1929 and 1934. Since she was born in 1916, I imagine it was purchased towards the end of this time period. It was equipped with a bellows, and used 127 film, which was 46 mm wide. It produced negatives that were 40 x 60 mm. The reason I used this was to take photomicrographs, especially of small marine and fresh water plants that I had collected trailing a plankton net behind my 2.4 m long Sabot sailing dinghy. I used black and white film exclusively. This camera rested on the eyepiece of my microscope, while a 30 second time exposure was made.

More modern cameras suitable for use with modern microscopes will be discussed in Optics 9 Microscopes, scheduled for publication on 2025-02-01.

In grade 12, I was tasked as the official student photographer for my high-school newspaper and year book, I used a 35 mm camera for the first time. It was a Contax II, that was used with Kodak Tri-X black and white film with high speed 400 ASA, which was purchased in 35mm x 100 foot lengths. In the school darkroom, I would load film onto cassettes. Because the camera lacked flash possibilities, dark situations often required that I push the film to ASA 1600, and develop it accordingly. Unfortunately, this increased the film’s grain structure. Kodak, attempted to market this as adding a level of realism to photographs. I was never convinced.

I developed all of the film I used, then spent numerous hours making prints with an enlarger. Working alone, and in the dark, except for a red light, this was the process I liked the most. In essence an enlarger is a camera with a light at the top, that projects a negative image onto photographic paper. One could set the aperture opening, and the exposure time. In this case there was a large timer that controlled the light inside the enlarger, then counted down the seconds before turning off the light. It was 1960s automation.

I am not sure how many times I visited the local camera shop on 6th Avenue in New Westminster. I was interested in an Asahi Pentax Spotmatic camera. It used a Through The Lens (TTL) centre-weighted light meter. This camera allowed one to focus the lens at maximum aperture with a bright viewfinder image. After focusing, a switch on the side of the lens mount stopped the lens down and switched on the metering which the camera displayed with a needle located on the side of the viewfinder. This stop-down light metering was innovative, but it limited the light meter, especially in low light situations. A M42 screw-thread lens mount was used to accommodate high quality Takumar lenses. This meant that it took considerably longer to change lenses, than with a bayonet mount.

Exakta VXIIb

Unfortunately, I could never afford to buy a Pentax. Some years later, in 1973 or so, I bought my first camera, a used Exakta Varex IIb called an Exakta VXIIb in USA. It was a 35 mm camera, produced between 1963-67, and referred to as version 6. Film speeds could be set on the top of the shutter speed dial. Shutter speeds followed the modern geometric progression from 1/30 to 1/1000 second. The rewind knob has a crank handle, but there was no view-finder release knob. The camera did not have a built-in metering system, but I had a hand-held light meter. Despite, this limitation, I especially liked the camera for two reasons. First, it came with a bayonet mount system for interchangeable lenses. Second, and more unusually, it allowed interchangeable view-finders. I had two, a pentaprism as used on most 35 mm cameras, and another one that allowed viewing from the top. This was especially useful when I studied archaeology, because it could take photos of an archeological excavation’s stratigraphy = cultural layers.

Exakta is no longer a recognizable brand, but James Stewart (1908 – 1997)/ L. B. Jefferies and Grace Kelly (1929 – 1982) / Lisa Fremont used one attached to a Kilfitt 400 mm f5.6 lens in Alfred Hitchcock’s (1899 – 1980) Rear Window (1954). It is one of the most iconic cameras in film history.

With this new camera, I switched to Illford Pan F black and white film with ASA 50 film speed, which, with its fine grain, suited my personality better. I have never been a user of colour negative film, but with this camera used Ektachrome, a slide/ transparency film that was developed by Kodak in the early 1940s. It allowed both professionals and amateurs the opportunity to process their own films. I always used the ASA 64 version, because it gave better results than High Speed Ektachrome, announced in 1959 with ASA 160. At the time, many north Americans were Kodachrome enthusiasts. However, it required professional processing.

Ektachrome processing is simpler, and small professional labs could afford equipment to develop the film. I used the E-6 process variant. which allowed amateurs with a basic film tank and tempering bath to maintain the temperature at 38 °C, to obtain suitable results.

Yashica FX-2

A Yashica FX-2 35 mm Camera Photo: Joe Haupt

After Trish and I married, we bought ourselves a modern Yashica FX-2 35mm single lens reflex (SLR) camera. This type of camera was manufactured in Japan, starting in 1976. It was Yashica’s second camera to use the new bayonet lens mount known alternately as the Contax/Yashica = C/Y mount. The intended advantage was that one could start off with inexpensive Yashica lenses, then progress to better quality Contax lenses when finances allowed it. In reality, one stuck with Yashica lenses because they were more robust than the more delicate Contax lenses.

Its viewfinder provided 0.89x magnification and nearly 90% field of view. The through the lens (TTL) light meter used Cadmium sulfide (CdS) as a photoconductive material in its photoresistor. The film speed could be set from 12 ASA to 1600 ASA. There is not much film that is sold over 400 ASA. However, this allowed users to set the film speed that the film woud be developed at. This is an important characteristic for that group of people.

The results of this metering was shown with a needle on the right side of the viewfinder display. When a proper shutter speed and aperture opening combination was selected, a proper exposure would result with the needle between the + and −. Manual focus is provided by manually turning the lens to the left (closer) or right (further away).

One could always see how a particular aperture opening would affect focus by pressing a depth of field preview button, located at the base of the lens. The light meter was powered with a 1.3v mercury battery (EP-675R, RM-675R, or equivalent) located underneath the camera, Its housing could be opened with a coin. Yes, younger readers may need to understand that smaller units of currency involved small round pieces of metal that were often carried in wallets or pockets. These days it would be considerably easier for me to find a slotted screwdriver than a coin. Yes, technology changes.

It was a very easy camera to use, and conventional for the period. The focal plane shutter operated from 1/1000 to 1 sec and B = bulb. If one needed a longer shutter opening than 1 second, then one set it to B, and held the shutter open for as long as one wanted. To use it properly, the camera would have to be mounted on a tripod, with the exposure made using a cable release. A flash could by synchronized by using X sync at speeds from 1/60 and slower. A self-timer was built into the camera. This gave the photographer about 10 seconds to position her/himself.

The mass of the camera body (without lenses) = 690 g. Camera dimensions were: 144.5 x 94 x 51 mm.

With this camera, my darkroom career almost ended, although I continued to develop black and white film. For colour slides, we increasingly used Fujichrome, usually Fujichrome 64.

Tripods

While I have learned to brace myself to take photographs without tripods, they are useful! Of course, to take full advantage of a tripod, one should use a cable release = threaded cable release = a device used to actuate the shutter of a camera without touching the shutter button. It consists of a flexible wire moving within a sheath, with a threaded connector on one end, an a plunger on the other. The sheath is usually vinyl. It is purely mechanical, in contrast to an electronic remote shutter release.

At one time I found a used tripod on sale for less than a reasonable price, I bought it, so that I could give it away to someone with an unmet and often unrealized need. So, my gift suggestion is for people to stock up on unusual, inexpensive used items that can be given away. They make much nicer gifts than yet another box of chocolates that people will despise you for because they went up an additional 100 g, eating those unnecessary calories!

This is the last camera that will be discussed here. We bought one additional 35mm SLR camera before entering the digital age. It claimed to be more modern, but my favourite camera will always remain the Yashica FX-2.

In much the same way that I have an aversion of audiophiles, who claim to hear music much better than their anatomy is capable of perceiving, there are terms to describe two types of annoying users of cameras. In Swedish, the term linslus with lins = lens & lus = louse, refers to someone obsessed with being photographed. In English, that person could be called a lenslouse. A person obsessed with taking photographs is a shutter bug. It is a kinder term, if only because I include myself in that category. These two terms cover annoying people in front of, or behind the camera, respectively.

Yes, I would like to encourage other people to share their thoughts/ experiences about analogue photography, by making comments or sending an email to me.

On 2024-04-27 this post was scheduled to be published on 2025-01-04 at 12:00. Sometime later that was changed to 2025-01-11 at 18:00.

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Optics 5

This weblog post is the fifth of a series of nine, about optics and optical equipment. This post is about safety glasses/ goggles and other equipment to protect the eyes.

Bluewear Raptor safety glasses are a personal favourite for eye protection inside a workshop.

Our household has numerous personal protective equipment (PPE) items available for people to use. Almost all items have been sold as Bluewear, a clothing and accessory brand of Jula, a company that was started at Skara, near Goteborg in south-west Sweden in 1979. Bluewear is a wordplay on the Swedish Blåkläder = blue clothes, a company that was started at Svenljunga, also near Goteborg, in 1959. It has developed a major American presence, today. We often compare safety equipment with the brands offered by Biltema and Clas Ohlsen, as well as Coop. Their house brand products are similar, and typically cost about 50% of the price charged for 3M and Caterpillar equipment. The main criteria for selecting protective equipment are: 1) that it meets appropriate safety standards, and 2) that it is comfortable to wear. The international brands typically emphasize (read: market) a specific specification. Often this is lower than that provided by the house brands.

Protective eyewear (PPEE) conform to EN 166, the European standard. At Cliff Cottage, almost every PPE item is different, because together they constitute a collection. In much the same way that other people may collect stamps, I like to collect PPEs that are diverse and designed to counter a variety of risks. In terms of eyewear these include splatter, impact and light filtration, including UV light. Currently, none are designed to withstand molten metal. In many situations, eyes need protection from foreign objects, such as dust particles, caustic fluids and metal swarf shavings. Eye protection should be worn even if there is no immediate risk.

PPEEs tends to be split into four categories: safety glasses, goggles, visors/face shields and sunglasses. Currently, there is no welding equipment in our workshop, but should this situation change, a fifth category of eyewear would also be needed.

Separate tests are undertaken to ensure suitability against: droplets or splashes of liquids, large dust particles, gases and fine dust particle, short circuit electric arcs, molten metals and hot solids, surface damage by fine particles, fogging, enhanced infrared reflectance, have replacement oculars. Not all products pass all of the tests. Not all products offer the same level of protection, even if they meet the standard, generally.

One also wants protective items to fit and be comfortable. Here, individuals may find one item fits better than another. For me, the house brands are suitable, and I see no need to buy international brands. Confession: I own three pairs of socks labeled with a yellow CAT name. They were bought because they were cheaper than everything else. When I wear them, sometimes people comment. I then feign an appreciation of felines. It is a total misrepresentation. I could never own (or allow myself to be owned by) a cat, because they kill too many birds!

Safety glasses

Bluewear Cobra safety glasses.

Glasses are the simplest form of eye protection. They come with a rod/ temple on each side that are bent, and end in an ear piece. These are worn over the ear. The main advantage with them is that they are simple and cheap. However, they are not particularly effective in preventing saw dust from reaching eyes. Thus, I seldom use them when working with electric saws.

One can buy 10 Bluewear Cobra safety glasses for the price of a single 3M brand equivalent. We have four, suitable for visitors to the workshop, not undertaking any work. They cannor be adjusted, are more easily scratched, and can fog up. We also have two pairs of slightly better Bluewear Atrax safety glasses, that are less easy to scratch, avoid fogging and are adjustable. They cost about three times more than the Cobra model. These can be used by people working, in the workshop or elsewhere.

Safety goggles

Googles are similar to glasses, but offer increased protection. They are typically fastened with a strap. The main advantage with them is that prescription glasses can be worn inside them. So people with this need should probably use them. However, it should be noted that safety protection equipment worn over glasses may transmit forces through the eye glasses, placing the user at risk! Goggles are effective in preventing saw dust from reaching eyes.

Personally, I use Raptor PPEEs (see photo at top of post) that are somewhere between goggles and glasses, have both temples and straps. These cannot be combined with glasses. These are most often worn when working with electrical tools in a workshop situation, especially with mitre saws and rip saws.

Face shields

Some face shields are inappropriate despite meeting EN166 standards. They may protect eyes, but they prohibit the wearing of ear protection, often called ear defenders. I refuse to buy/ use these. Instead I have a combined helmet with hearing protection, a poly-carbonate face shield and a mesh = metal netting face shield, only one of these last two can be worn at a time.

In addition to meeting the EN166 standard, these meet the EN 397 (industrial hard hats), EN 1731 (mesh protectors for chain saws), and EN 352-3 (Hearing protectors that are designed to be attached to industrial safety helmets) standards. This equipment is suitable for working outdoors with chainsaws, clearing saws, trimmers but even less dangerous equipment such as lawn mowers. The total price of such equipment is about half that with the three products bought separately.

Sunglasses

Bluewear Nepture safety glasses with dark lenses.

There are two types of safety glasses with dark lenses available at Cliff Cottage. Bluewear Achillo and Bluewear Neptune. Both have partial frames and dark lenses that have been specially treated to give a scratch-free and fog-free surface. Both have rubber-coated rods make the frame comfortable to wear and keep the glasses in place. These can be used when using a lawn mower or garden trimmer. I use a Neptune for outdoor construction work. It fits larger faces. The Achillo fits smaller adult faces; Neptune fits larger faces.

Note: This post was started on 2024-04-27 at 18:00. It was based, in part, on notes taken as an employee at assorted schools. In addition, for five years I commuted with Victor Nilsen (1953 – ), who was chief steward at Romsdal upper secondary school. Our conversations provided me with a lot of anecdotal information about health and safety issues.

Welding helmet

Modern welding helmets are described as automatic. This means that they are fitted with a glass cassette containing liquid crystals typically activated (auto-darken) by an electronic control unit within 100 – 400 µs. The legal limit is 10s which is up to 10 000 times shower, and totally unacceptable in real life. The field of view varies, but many welders find 100 x 67 mm window acceptable, although larger sizes are available, at increased price. The degree of darkness is easily adjustable (5-13 DIN) with 13 being the darkest. There is usually an adjustment knob on the side of the helmet. Some helmets have a lower angle grinder mode with dimming to 4 DIN. Fieldwork and high amperages require helmets with fixed darkening.

Most welding activities undertaken by amateurs can use auto-darkening. Low amperage tungsten inert gas (TIG) welding is a precise and versatile process used to create high-quality welds. It joins metals using a non-consumable tungsten electrode while protecting the welding area from atmospheric contamination with an inert gas such as argon. The shielding gas prevents oxides and nitrides from forming in the weld. Metal inert/ active gas (MIG/MAG) are similar. The most important active gas is CO2. Manual metal arc welding (MMA) uses a flux for shielding. A variety of light sensors can be used to activate darkness.

Welding helmets provide other features. Cheater lenses magnify the view of the work.

Rechargeable batteries can be used to power sensors and liquid crystal cassettes. Some helmets can be plugged in to be recharged or use solar cells. In the future, smart welding helmets will have cameras, and bluetooth connectivity, allowing the welder to communicate through other devices.

Respiratory welding helmets = Powered Air Purifying Respirator (PAPR) masks protect lungs while allowing the welder to breathe normally. They are equipped with external blower units with changeable filters connected by a thick hose for sufficient airflow. Most people prefer an adjustable helmet, with a padded headband.

Welding helmets are often made of ABS plastic. It is cheap, lightweight, sturdy, durable and is a poor thermal conductor. It comes in a matt finish. The alternative is fibreglass. It has high tensile strength, absorbs vibrations and insulates sounds. Given a choice and a large enough budget most welders choose fibreglass!

Favourites

Bluewear Raptor safety glasses pictured at the top are my favourite because they are comfortable, and meet most of my needs. They have soft padding around the eyes and a removable strap. Both are useful to prevent the glasses from moving/ slipping off. The safety glasses are equipped with scratch-resistant and anti-fog-treated clear glass, so that the glasses provide good visibility and have a long lifespan. Unfortunately, because of my light sensitivity, I prefer not to wear these outdoors. Instead, I use Bluewear Nepture dark lens safety glasses.

Welding is not an activity I engage in often, so I do not have a valid opinion about safety equipment.

Note: Originally, this post contained general information about household health and safety stewardship. On 2024-06-21 at 07:30, this content was moved to its own post to be published on 2024-07-27 at 12:00 (Norwegian time).

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Optics 4

This weblog post is the fourth of a series of nine about optics and optical equipment. This post is about eyeglasses, including sunglasses. Towards the end I also make some comments on glasses for reading, as well as being used with assorted screens.

Eyeglasses

Both Trish and I have used eyeglasses since we were 13. Yes, since puberty.

We have renounced the discount optical retailers found everywhere in the world, locally in Levanger and Steinkjer, cities 40 km south and 35 km north of us, respectively. We now patronize the optician located at our former bank building in Straumen, about 13 km east of our house. Husby Optikk was founded in 1854 in Steinkjer. Anne Sofie Staven Husby, the niece of a neighbour, has run the Inderøy branch since it opened in 2020. I suspect she met her husband, Terje, who runs the larger, Steinkjer branch, while they both studied to be opticians in Copenhagen.

Trish’s regular eyeglasses are in frames made by Kuno-Qvist. a Swedish firm founded in 2004, and located in the Norra Sorgenfri industrial area of Malmö. Its motto is Always in character. Her Khantra 52-18 model offers metal frames with blue and brown highlights: with a feather like pleated metal pattern,… [that] will evoke a feeling of movement in the frame when the wearer moves. Trish always enjoys blue, and in this case it matches the colour of her eyes.

My regular eyeglasses are housed in frames made by Face a Face, Paris. It calls itself an audacious, non-conformist eyewear brand. That definitely suits my personality. Despite its French origins in 1995, it now has its headquarters in Aarhus, Denmark. The model I use is called Kieth 3, and is made in opaque fluid yellow. These frames are an extreme bright yellow. I had asked Anne Sofie to find frames in signal yellow, and I am more than pleased with the result.

Sunglasses

Both Trish and I use sunglasses made to our individual prescriptions, with polarized glass. We may need these to drive legally with sunglasses, but also prefer to view the world through corrected lenses.

As usual, Trish invested in Maui Jim Koki Beach sunglasses first. I would describe these sunglasses as basic. Trish’s eyes still function as intended/ designed. She does not need extreme features. These provide everything that is needed, but nothing more, including a clear, glare-free view of the world. The name comes from a beach on Maui’s east shore.

I have started to prioritize the selection and care of sunglasses, because of the challenges I have with my eyes. I want sunglasses that feel comfortable, and are kind to my eyes. I use sunglasses for driving, more often than I use conventional glasses. Compared to Trish, I need greater protection from glare. This includes winter glare from snow. Thus, I felt that Maui Jim Southern Cross = Hanaiakamalama (Hawaiian) with their polarized wrap were better at meeting my sunglass needs. Other features, such as a triple-injected nylon frame in Soft Black with Sea Blue and Grey, were nice to have.

In 1980, Jim Richards, a fisherman, began selling sunglasses on the beaches of Maui, Hawaii. Some years later, the company developed polarized sunglasses to protect eyes from glare and UV light. In 1991, Walter Hester, a boat captain, purchased and rebuilt the company, calling it Hester Enterprises, Inc. By 1994, the company was named Maui Jim Sunglasses, and allowed Illinois-based RLI Vision to become its mainland distributor. In 1996, Maui Jim Sunglasses bought RLI Vision from its parent company, Peoria, Illinois-based RLI Corporation to form Maui Jim Inc. The corporate headquarters is in Peoria, but there is a branch office in Maui. In 2004, the company opened a distribution center in Braunschweig, Germany. It later became its European headquarters.

Part of the reason why I think I will stick with Maui Jim as a brand was an earlier work related trip to Sicily when people with fake Ray-Ban sunglasses were issued an €800 fine by the customs authorities in Italy. At the time, I was wearing real Ray-Bans, but I found the incident so offensive, that I vowed never to buy Ray-Bans again. I haven’t.

Other eyeglasses

There are several other types of glasses available. At one time, I used reading glasses. As I aged I found it better just to remove the glasses. I was able to read just as well. Many people experience the opposite. They need some form of reading glasses.

My former employer, Nord-Trøndelag county, encouraged the use of device/ computer glasses. There was a claim that using them make made work with a screen more comfortable. One point that is often taken up involve blue light. Electronic device screens radiate many colours, including blue, with wavelengths from about 400 nm to 495 nm. Some people are affected by blue light. Blue light can be divided into two bands, blue-violet light (400-455 nm) and blue-turquoise light (465-495 nm). Sleep/wake = circadian cycles are impacted by blue-turquoise light, but not blue-violet light. The main source of all forms of blue light is sunlight. Device glasses typically filter blue-violet light, but not blue-turquoise light, that impacts the circadian rhythm. My experience of using device glasses, is that they are not particularly helpful. I do not currently use them.

Displays/ Screens

I use three very different displays/ screens with my computing devices: a hand-held device/ smart phone with a 5.9″ display = 1080 x 2400 pixels; a laptop with a 14″ display = 1920 x 1080 pixels; and a desktop with a QHD 27″ display = 2560 × 1440 pixels. The last one is best when my eyes feel strained. About four years ago it replaced another 27″ display with HD resolution = 1920 x 1080 pixels, that I had used for twelve years. I find that the increased resolution, rather than the screen size, most helpful. For me, the most effective improvement comes from using a dark background.

Trish does not use glasses when working with computer screens, either. She has almost identical devices to mine, but on her desktop machine she but prefers to use a 24″ HD display. Yes, she was offered an identical QHD 27″ display, but declined. In addition, she uses two Kobo e-readers, a black Glo HD (N437) with a 6″ display = 1448 x 1072 pixels (for fiction) , and a white Libra H2O (N873) with a 7″ display = 1680 x 1264 pixels (for non-fiction). I have tried to use Kobos, but prefer to read paper books.

The main rule seems to be that everyone is different.

Note: This post was originally written early in the morning of Monday 2024-03-18, under the title Magnification. Later in the day that was changed to Optics. It was saved using that new title, for the first time, at 18:10. It was then split into four posts, later expanded to five, on 2024-03-23. On 2024-04-09 at 20:00 the first post was scheduled to be published 2024-06-01 at 12:00.

Note: I appreciate detailed information. At times, I even refer to myself as a detailist. When it comes to products I own and use, including eyeglasses, I want to know who designed it, and why it was designed the way it was. I want to know product history, how and why a product evolved. I am fascinated by the techniques used to fabricate items. Of course, I want to know where things are made. The name of a country is seldom enough of an answer. I want a much more specific location, if possible a street address, and – for the past couple of decades – an image of that location, if only from Google Streetview.

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Optics 3

This weblog post is the third of a series of nine about optics and optical equipment. This post is about deviations from normal sight, that can be corrected with eyeglasses, including sunglasses, or contact lenses.

Eye correction is important because many optical devices, such as telescopes, microscopes and cameras require manual adjustments to optimize results. This situation may not be too important if the device is being used directly to look at objects. However, if the device is being used indirectly to create images, uncorrected eyes may result in out of focus = blurred images, that may be anywhere from difficult to impossible to correct.

In the early 1970s, I spent a lot of time taking photographs with a friend who was losing his sight. He used photography to see his world before it dimmed forever. This situation has had a major impact on my attitudes toward vision, and photography.

In 2019, I wrote a weblog post about visual acuity, Optotypes. Acuity tests measure how sharp a person’s vision is at a distance. In many places it is tested using a Snellen eye chart, with rows of letters in decreasing sizes. It is read at a distance of 6m = 20′, although if mirror reflection is used, the distance can be reduced to 3m = 10 feet. I remember, at the age of 13, I asked the school nurse about my blurred vision. She gave me a Snellen test and said I should have my eyes tested. Shortly after this, I was wearing glasses. In many places, especially in Europe, the Landolt C test has replaced the Snellen test. This asks a patient to tell where the opening of a letter C is. The letter can be orientated in any of eight different positions, at 45 degrees from each other. Acuity tests, with the patient using her/ his ordinary prescription lenses, are used in many jurisdictions to prohibit people from driving. Unacceptable results in a darkened room, can be used to prohibit driving after dark.

In Optics 1, it was noted that Ibn al-Haytham in his Book of Optics (1021) along with Roger Bacon‘s written works on optics, described the function of corrective lenses for vision.

Reading stones, often used by monks when they illuminated manuscripts, were invented at some point between the 11th and 13th century. These were primitive plano-convex lenses (see illustration above) initially made by cutting a glass sphere in half. As the stones were experimented with, it was slowly understood that shallower lenses magnified more effectively. Around 1286, possibly in Pisa, Italy, the first pair of eyeglasses were made, although it is unclear who the inventor was.

There are several types of eye care/ health professions. The distinctions between them varies, depending on the jurisdiction regulating them. The text below is intended to give a flavour of the various professions, not rigorous legal definitions.

Ocularists make and fit ocular prostheses for people who have lost eyes due to trauma or illness.

Opticians make and fit ophthalmic lenses, spectacles = eyeglasses, contact lenses, low vision aids and ocular prosthetics.

The most problematic term is optometrist. In some jurisdictions it is a person with medical education, with an authorization to perform eye surgery. In others, the scope is more limited. Thus, some are trained and licensed to manage any eye disease, including infections, glaucoma and macular degeneration. Many can prescribe topical medications = eye drops, fewer can prescribe controlled ingested substances. Some may order imaging tests (CT/MRI), remove ocular foreign bodies and perform some laser procedures. Some are also qualified to perform some surgical procedures.

Orthoptists diagnose and manage eye movement and coordination problems, such as misalignment of the visual axis, binocular vision problems, convergence and accommodation problems, and pre/post surgical care of patients with: amblyopia (see below) and strabismus = a vision disorder in which the eyes do not properly align with each other when looking at an object. They treat patients using optical aids and eye exercises, but not with medications or surgery.

An ophthalmist is a physician who specializes in serious eye conditions, but is not a surgeon.

Ophthalmology is a surgical subspecialization that handles the diagnosis and treatment of eye disorders. Ophthalmologists are physicians that undergo subspecialty training in medical and surgical eye care.

Eyewear prescriptions

Corrective lenses are typically prescribed by an ophthalmologist or an optometrist. The prescription consists of all the specifications necessary to make the lenses, typically two! Typically the following information is included: the strength of each lens in quarter-diopter steps (0.25 D). Most people cannot generally distinguish between smaller increments. The use of improper corrective lenses may not be helpful and can even exacerbate binocular vision disorders. The goal is to provide the clearest, most comfortable, and most efficient vision, avoiding double vision and maximizing binocularity.

Eyewear is fragile. Many people have a service card they carry with them when travelling that specifies their eyeglass prescription. Hopefully, this will allow new glasses to be made anywhere in the world.

An eyewear prescription is a written order by an eyewear prescriber, that specifies the value of all parameters the prescriber has deemed necessary to construct appropriate corrective lenses for a patient. In Norway, and many other jurisdictions, most often the person performing the eye examination is also the same person selling you the glasses.

The parameters specified on eyewear prescriptions vary, but typically include the patient’s name, power of the lenses, any prism to be included, the pupillary distance, expiration date, and the prescriber’s signature. The prescription is typically determined during a refraction, using a phoropter and asking the patient which of two lenses is better, or by an automated refractor, or through the technique of retinoscopy. A dispensing optician will take a prescription written by an optometrist and order and/or assemble the frames and lenses to then be dispensed to the patient.

Sphere component

Because its shape minimizes some aberrations, convex-concave lenses (see the diagram at the beginning of this post) are most commonly used in corrective lenses. These can be defined as transmissive optical devices worn in front of the eye to improve visual perception.

Eyeglasses = spectacles are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted, most commonly after cataract removal.

Every corrective lens prescription includes a spherical correction in diopters. Convergent powers are positive (e.g., +4.00 D) and condense light to correct for farsightedness/long-sightedness (hyperopia) or allow the patient to read more comfortably (see presbyopia and binocular vision disorders). Divergent powers are negative (e.g., −3.75 D) and spread out light to correct for nearsightedness/short-sightedness (myopia). If neither convergence nor divergence is required in the prescription, “plano” is used to denote a refractive power of zero.

The term sphere comes from the geometry of lenses. Lenses derive their power from curved surfaces. A spherical lens has the same curvature in every direction perpendicular to the optical axis. Spherical lenses are adequate correction when a person has no astigmatism. To correct for astigmatism, the “cylinder” and “axis” components specify how a particular lens is different from a lens composed of purely spherical surfaces.

Cylinder component

Patients with astigmatism need a cylindrical lens, or more generally a toric lens to see clearly. The geometry of a toric lens focuses light differently in different meridians. A meridian, in this case, is a plane that is incident with the optical axis. For example, a toric lens, when rotated correctly, could focus an object to the image of a horizontal line at one focal distance while focusing a vertical line to a separate focal distance.

The power of a toric lens can be specified by describing how the cylinder (the meridian that is most different from the spherical power) differs from the spherical power. Power evenly transitions between the two powers as you move from the meridian with the most convergence to the meridian with the least convergence. For regular toric lenses, these powers are perpendicular to each other and their location relative to vertical and horizontal are specified by the axis component. By convention, a horizontal axis is recorded as 180° meridians. The 90° meridian defines the vertical axis.

There are two different conventions for indicating the amount of cylinder: “plus cylinder notation” and “minus cylinder notation”. In the former, the cylinder power is a number of diopters more convergent than the sphere power. That means the spherical power describes the most divergent meridian and the cylindrical component describes the most convergent. In the minus cylinder notation, the cylinder power is a number of diopters more divergent than the sphere component. In this convention, the sphere power describes the most convergent meridian and the cylinder component describes the most divergent. Europe typically follows the plus cylinder convention while in the United States the minus cylinder notation is used by optometrists and the plus cylinder notation is used by ophthalmologists. Minus cylinder notation is also more common in Asia, although either style may be encountered there. There is no difference in these forms of notation and it is easy to convert between them:[1]

  • Add the sphere and cylinder numbers together to produce the converted sphere
  • Invert the sign of cylinder value
  • Add 90° to axis value, and if the new axis value exceeds 180°, subtract 180° from the result

For example, a lens with a vertical power of −3.75 and a horizontal power of −2.25 could be specified as either −2.25 −1.50 × 180 or −3.75 +1.50 × 090.

Axis component

The axis defines the location of the sphere and cylinder powers. The name axis comes from the concept of generating a cylinder by rotating a line around an axis. The curve of that cylinder is 90° from that axis of rotation.

The most common use is to treat refractive errors: myopia = near-sightedness = short-sightedness = a condition where incoming light focuses in front of, instead of on, the retina; hypermetropia = hyperopia = far-sightedness = long-sightedness = a condition where incoming light focuses behind, instead of on, the retina; condition of the eye where distant objects are seen clearly but near objects appear blurred ; astigmatism = rotational asymmetry resulting in distorted or blurred vision. If it occurs in early life and is left untreated, it may result in amblyopia = lazy eye = a disorder where the brain fails to fully process input from one eye and favors the other eye, over time resulting in decreased vision in an eye that typically appears normal in other aspects; and presbyopia = age-related farsightedness = physiological accommodation insufficiency associated with aging (typically people aged over 40) resulting in a progressively worsening ability to focus clearly on close objects.

Contact lenses

There are five types of contact lenses, based on type of lens material: 1) Polymethyl methacrylate (PMMA) lenses have excellent optics, but they do not transmit oxygen to the eye and can be difficult to adapt to. They are considered old fashioned. 2) Rigid gas permeable lenses (RGP) look and feel like PMMA lenses but are porous and allow oxygen to pass through them. They can be fit closer to the eye than PMMA lenses, making them more comfortable. They were introduced in 1978. 3) Hydrogel lenses are thin and pliable = soft, and conform to the front surface of the eye. These were introduced in the early 1970s. They made contact lens wear much more popular because they typically are immediately comfortable. 4) Silicone hydrogel lenses are an advanced type of soft contact lenses that are more porous than regular hydrogel lenses and allow even more oxygen to reach the cornea. These were introduced in 2002, and are now the most popular lenses prescribed in economically advanced countries. 5) Hybrid contact lenses provide wearing comfort similar to soft or silicone hydrogel lenses, but combine this with the clear optics of gas permeable lenses, due to a skirt of hydrogel or silicone hydrogel material. These lenses are difficult to fit and are more expensive to replace than other types. Only a small percentage of people wear hybrid contact lenses.

Once again there is a distinction made between spherical and toric lenses. Spherical contact lenses have the same lens power throughout the entire optical part of the lens. This means they can be used to correct myopia (nearsightedness) or hyperopia (farsightedness). Toric lenses allow contact lenses to correct for astigmatism.

At one time, contact lenses had to be changed every day. They were then cleaned, then stored in an appropriate container, with solution, over night. Then the maximum duration extended, soon becoming once a week, for certain types. Now 30 days is considered the legal maximum.

In our nuclear family, the use of contact lenses is extremely limited. Non-existent is incorrect, because one person decided that it would be best to use these at her wedding, so that her glasses would not date the event.

Notes

Recently, I was asked why I write weblog posts that remind people of Wikipedia articles. They suggested I should spend my time writing autobiographical materials about my life. Part of the reason has to do with my career as a teacher. My main task was to explain how the world operates. In addition, I am perpetually creating user manuals, usually for an audience of one. However, publishing them as blogs, allows more people to access the content.

Because the content is originally produced just for my own consumption, sources are seldom specified.

On 2024-04-27, this post, also called Optics 3, was started. By the end of the day, it had been divided into three, with this section being about eye prescriptions. The next post was renamed Optics 4, about eyeglasses. It is to be published on 2024-06-22. Optics 5 is about various types of safety glasses. This post is to be published on 2024-06-29.

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Optics 2

Eyes. Photo: Manuel Meurisse, 2017-11-17, Tasmania, Australia

This is the second of nine posts about optics.

Optical devices interact with eyes and a brain, so that the content being observed can be interpreted relevantly. Cameras, binoculars, microscopes and other analogue optical devices, can subject eyes to excessive strains. For example, looking even indirectly at the sun during a solar eclipse using inappropriate aids, invites permanent damage to the eyes. Optics mediated through a digital screen are less problematic, because the screens come equipped with limits on their optical capabilities. That said, screen brightness settings can be excessive, either too low or too high for the eyes using them. Personally, I routinely set my digital devices to 20% of the maximum allowable. I also select black backgrounds. I have often wondered if this light sensitivity is related to my blue eyes. Other people may have completely different needs.

Vision changes

As a person ages, it is common for them to find that they can’t see as well as they once did. That’s a normal development. They will probably need glasses or contacts. If a person already uses them, they may need a stronger prescription. Some people may choose to have Laser-Assisted in Situ Keratomileusis (LASIK), commonly referred to as laser eye surgery or laser vision correction. There are mixed opinions (and little scientific evidence, as far as I can find) about the suitability of LASIK.

Presbyopia is the name given to the situation where a person loses the ability, despite good distance vision, to see close objects and small print clearly. After age 40 or so, people may have to hold a book or other reading material farther away from their eyes to make it easier to read. Many complain that their arms are too short. Reading glasses, contact lenses, and other procedures can be used to restore good reading vision.

Other, more serious conditions also happen as people age. Eye diseases like macular degeneration, glaucoma and cataracts, can cause vision problems. Symptoms vary a lot among these disorders.

Colour blindness

When a person cannot see certain colors, or can’t tell the difference between them (usually reds and greens), that person may be colour blind. It happens when the cone cells, used to distinguish colour, are absent or fail to work. When it is most severe, a person can only see in shades of gray, but this is rare. Most people who have colour blindness are born with it, but one can get it later in life from certain drugs and diseases. Men are much more likely to be born with it than women.

Paddy, the father of my wife, Trish, had red-green colour blindness, so I have been concerned about people inheriting this. There are free online colour blindness tests. I have taken one here, and found that I have normal vision. There’s no treatment if a person is born colour blind, but special contacts and glasses can help some people tell the difference between certain colors.

My son, Alasdair, has also taken numerous colorblindness tests with no indication of colour blindness. In middle school he created such a test and was able to diagnose one of his peers as colour blind. Until then, this child was unaware of his condition. My daughter, Shelagh, informs me that it’s common practice in web development to check designs to ensure they pass colour blindness tests.

Eyestrain

Eyes can be overused. They get tired and need to rest. Give eyes that feel strained time off.

Red Eye

The surface of eyes is covered in blood vessels that expand when they’re irritated or infected. That gives eyes a red look. It can be caused by eyestrain, a lack of sleep, allergies, or something more serious: an injury, conjunctivitis (pinkeye) or sun damage. Over-the-counter eye drops can sometimes help, along with rest.

Amblyopia

Amblyopia = Lazy eye is a situation where one eye does not develop properly. Vision is weaker in that eye, and it tends to move “lazily” around while the other eye stays put. It’s found in infants, children, and adults, but rarely affects both eyes. Treatment needs to be sought immediately for infants and children.

Lifelong vision problems can be avoided if this is detected and treated during early childhood. Treatment includes corrective glasses or contact lenses and using a patch or other strategies to make a child use the lazy eye.

Strabismus

If both eyes aren’t lined up with each other when one is looking at something, the problem could be strabismus = crossed eyes = walleye. This problem is often corrected using vision therapy, where weak eye muscles are strengthened. At other times, surgery is necessary.

Nystagmus

With nystagmus, an eye moves/ jiggles all the time on its own. Vision therapy is one treatment option. Surgery is another.

Uveitis

Uveitis is the name for a group of diseases that cause inflammation of the uvea, the middle layer of the eye that contains most of the blood vessels. These diseases can destroy eye tissue, and even cause eye loss. People with immune system conditions like AIDS, rheumatoid arthritis, or ulcerative colitis may be more susceptible to uveitis. Common ymptoms include: blurred vision; eye pain; eye redness; and, light sensitivity. Treatments vary, dependent on the type of disease.

Floaters

These are tiny spots or specks that float across a field of vision. Most people notice them in well-lit rooms or outdoors on a bright day.

Floaters are usually normal, but they sometimes can be a sign of a more serious eye problem, like retinal detachment. That’s when the retina at the back of an eye separates from the layer underneath. When this happens, a person might also see light flashes along with the floaters or a dark shadow come across the edge of their sight.

If a person notices a sudden change in the type or number of spots or flashes they see or a new dark “curtain” in appears in their peripheral vision, it is advisable to see an eye doctor as soon as possible.

Dry Eyes

This happens when eyes can’t make enough good-quality tears. A person might feel like something is in their eye or that it is burning. Rarely, in severe cases, extreme dryness can lead to some loss of vision. Some treatments include:

  • Using a humidifier
  • Special eye drops that work like real tears
  • Plugs in tear ducts to lessen drainage
  • Lipiflow, a procedure that uses heat and pressure to treat dry eyes
  • Testosterone eyelid cream
  • Nutritional supplements with fish oil and omega-3

If a dry eye problem is chronic, it could indicate dry eye disease. A doctor could prescribe medicated drops like cyclosporine (Cequa, Restasis), lifitegrast (Xiidra), or Tyrvaya nose spray to stimulate tear production.

Excess Tearing

It has nothing to do with feelings. A person might be sensitive to light, wind, or temperature changes. Try to protect eyes by shielding them or wearing sunglasses (go for wraparound frames — they block more wind than other types).

Tearing may also signal a more serious problem, like an eye infection or a blocked tear duct. An eye doctor can treat or correct both of these conditions.

Cataracts

These are cloudy areas that develop in the eye lens.

A healthy lens is clear like a camera’s. Light passes through it to the retina — the back of the eye where images are processed. With a cataract, light can’t get through as easily. The result: A person can’t see as well and may notice glare or a halo around lights at night.

Cataracts often form slowly. They don’t cause symptoms like pain, redness, or tearing in the eye.

Some stay small and don’t affect sight. If they do progress and affect vision, surgery almost always works to bring it back.

Glaucoma

An eye is like a tire: Some pressure inside it is normal and safe. But if levels are too high it can damage the optic nerve. Glaucoma is the name for a group of diseases that cause this condition.

A common form is primary open angle glaucoma. Most people who have it don’t have early symptoms or pain. This is often part of a regular eye examination.

Glaucoma can be caused by:

  • An injury to the eye
  • Blocked blood vessels
  • Inflammatory disorders of the eye

Treatment includes prescription eye drops or surgery.

Retinal Disorders

As previously noted, the retina is a thin lining on the back of the eye that is made up of cells that collect images and pass them on to the brain. Retinal disorders can damage retinal cells and block this transfer. There are different types:

  • Age-related macular degeneration refers to a breakdown of a small portion of the retina called the macula.
  • Diabetic retinopathy is damage to the blood vessels in the retina caused by diabetes.
  • Retinal detachment happens when the retina separates from the layer underneath.

It’s important to get an early diagnosis and have these conditions treated.

Conjunctivities (Pinkeye)

In this condition, tissue that lines the back of the eyelids covering the sclera gets inflamed. It can cause redness, itching, burning, tearing, discharge, or a feeling that something is in one’s eye.

People of all ages can get it. Causes include infection, exposure to chemicals and irritants, or allergies.

Wash hands often to lower chance of getting it.

Corneal Diseases

The cornea is the clear, dome-shaped “window” at the front of an eye. It helps to focus the light that comes in. Disease, infection, injury, and exposure to toxins can damage it. Signs include:

  • Red eyes
  • Watery eyes
  • Pain
  • Reduced vision, or a halo effect

The main treatment methods include:

  • A new eyeglasses or contacts prescription
  • Medicated eye drops
  • Surgery

Eyelid problems

Eyelids are important for: protecting eye, spreading tears over its surface, and limiting the amount of light that can enter.

Pain, itching, tearing, and sensitivity to light are common symptoms of eyelid problems. One might also have blinking spasms or inflamed outer edges near eyelashes.

Treatment could include proper cleaning, medication, or surgery.

Some vision changes can be dangerous and need immediate medical care. Anytime a person has a sudden loss of vision, or vision becomes blurry seek medical advice.

Contact Lenses

I have never used, nor wanted to use, contact lenses. However, I understand that cleanliness is essential for their use. Users are advised to follow the care guidelines that came with their prescription. There is a need for users to

  • Wash their hands before touching contact lenses.
  • Never use saliva to wet them.
  • Ensure the lenses fit properly, to avoid scratches.
  • Use eye drops that say they’re safe for contact lenses.
  • Never use homemade saline solutions. Even though some lenses are FDA-approved for sleeping in them, doing so raises the risk of a serious infection.

If a person does everything right and still have problems with contacts, see an eye doctor. The person might have allergies or dry eyes. Once the problem is known, a person can decide the best course of action, which could include opting to use glasses.

Night Blindness

Night blindness is more of a symptom, than a problem. Nearsightedness, cataracts, keratoconus, or a vitamin A deficiency can all provoke these symptoms, that can be treated. At other times it is a symptom of a degenerative retinal disease that usually can’t be treated.

Note: This post started as my personal checklist about eye health issues. However, it has been augmented with additional problems, that people may encounter. The content has been accumulated over a number of years from unremembered sources, including Wikipedia. Some of these issues will need medical attention, while others are more trivial. The challenge is distinguishing between the two. So if what appears to be a trivial complaint persists, it could be appropriate to seek medical attention, to make sure it is not a more serious problem.

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Optics 1

Structure of the Eye. Image: OpenStax College, 2013-06-19.

This weblog post is the first of a series of nine about optics and optical instruments. Five of these will be posted in 2024-06, and four in 2025-01. This post presents some definitions, and some elementary theory behind optics. #Optics 2 is about eyes and eye diseases; #3 is about eye prescriptions; #4 is about eyeglasses. Later topics include: #5 is about safety glasses; # 6 is about cameras; #7 is about binoculars and monoculars; # 8 is about astronomical telescopes; and, #9 is about microscopes.

There are two approaches to optics that can be taken: Here it is about visual perception, the eyes, and how they sense, rather than on the natural (or even the artificial) production of phenomena, such as light and colour, that can be observed.

Readers are advised against starting any study of optics with Greek philosophers. This will be discussed later in this weblog post. Instead, it they want a historical approach, an appropriate place to begin is The Book of Optics (1011-1021), a seven-volume treatise on optics and some other subjects by Ibn al-Haytham, (965–c. 1040) = Alhazen/ Alhacen, a medieval Arab scholar.

Ibn al-Haytham was the first to correctly explain the theory of vision, and to argue that vision occurs in the brain, noting that it is subjective and affected by personal experience. He stated the principle of least time for refraction that links ray optics and wave optics: the path taken by a ray between two given points is the path that can be traveled in the least time = Fermat’s principle. He made major contributions to catoptrics = the branch of optics dealing with the reflection of light from plane or curved mirrors, and dioptrics = refraction, especially by lenses. More generally, Ibn al-Haytham contended that a hypothesis must be supported by experiments based on confirmable procedures and/ or mathematical reasoning.

Content. Book I: theories about light, colours and vision; Book II: theory of visual perception; Book III: ideas on the errors in visual perception; Book IV and Book V provide experimental evidence for theories about reflection; Book VI: errors related to reflection; Book VII: the concept of refraction.

An appropriate next stop is the English bishop Robert Grosseteste (c. 1175–1253) who wrote on a wide range of scientific topics, that included On Light (1235), which is viewed from four different perspectives: epistemology, metaphysics/ cosmogony, etiology/ physics and theology. All of these take their inspiration from Genesis 1:3: God said, let there be light, Creation is seen as a natural physical process arising from an expanding/ contracting sphere of light.

A third stop is Roger Bacon (c. 1214–1294), an English Franciscan, who was influenced by Grosseteste’s writings. Perspectiva, Tractatus de multiplicatione specierum (<1267) = Tract on the Multiplication of Species, and De speculis comburentibus = On Burning Lenses are all writings about optics. His mathematical analysis of light/ vision was influenced by Ibn al-Haytham.

An erect image = one that appears right-side up. The opposite is an inverted image = one that appears upside down. Some telescopes and other devices including the camera obscura present an inverted image. Mirrors and compound prism elements can be used to transform an inverted image into an erect image.

Popularizations

Many times theorists have a difficult time explaining their subject so that it is understandable for a broader audience. At that point it is good to have other people around who are able to communicate ideas. Here are some of those people in the field of optics.

Peter of Limoges (1240–1306), in Tractatus Moralis de Oculo = A Moral Treatise on the Eye, popularized Bacon’s writings on optics.

John Pecham (ca. 1230 – 1292 ) wrote the most widely used optics textbook in the Middle Ages: Perspectiva communis. His book centered on the question of vision, on how we see. Pecham followed the model set forth by Ibn al-Haytham, but interpreted Ibn al-Haytham’s ideas in the manner of Roger Bacon.

Pseudoscience

When it comes to optics, early Greek philosophers are to be avoided. Empedocles (c. 494 – c. 434 BC) believed Aphrodite made the human eye out of the four elements = earth, air, fire, and water. She lit the fire in the eye which shone out from it, making sight possible. This would mean that it should be possible to see equally well in darkness as in light, which is not the case. He believed there were two different types of emanations that interacted: one from an object to the eye, another from the eye to an object.

In philosophy, William of Ockham (ca. 1287 – 1347) postulated Ockham’s razor , a problem-solving principle that recommends searching for simple explanations = the principle/ law of parsimony. It is expressed as: Entities must not be multiplied beyond necessity. It is often paraphrased as the simplest explanation is usually the best one. These Greek explanations contradict this advice.

There are few contemporary references to Euclid (c 300 BC) about optics. There are questions about the attributions of many of his works. He is believed to have written two books related to optics. Catoptrics, about the mathematical theory of mirrors, particularly images formed in plane and spherical concave mirrors. Optics is the earliest surviving Greek treatise on perspective, including an introduction to geometrical optics and basic rules of perspective.

Claudius Ptolemy (c. 100 – c. 170) of Greco-Egyptian ethnicity and Roman citizenship, flourished in Alexandria. Robert R. Newton (1918 – 1991) in The Crime of Claudius Ptolemy (1977) challenged Ptolemy’s observations and asserted that Ptolemy fabricated many of these to fit his theories. Newton accused Ptolemy of systematically inventing/ doctoring data, and called him the most successful fraud in the history of science.

Winer et al (2002) have found that up to 50% of adults in the early years of this millennium believed in emission theory. The easiest way to refute it is to note that if emission theory were true, it would be possible to observe objects in the dark equally well as objects in the daylight. I find there is a significant difference between these.

Note: In 2024-03 and 2024-04 I systematically investigated various topics related to optics. Much of it had to do with Trish having an eye examination on 2024-04-18. By 2024-04-09 at 20:11 I had decided where this series was going, and scheduled this post to be published 2024-06-01 at 12:00. We also decided that we needed new and lighter binoculars and a spotting scope so that we could be better oriented about the wildlife in our neighbourhood. In particular, I wanted to follow a pair of cranes (Grus grus), birds that live near us during the summer.

Corrections: On 2024-06-08, at about 18:40, the number of posts about optics in 2024-06 was increased from 4 to 5, while the number was decreased from 5 to 4 in 2025-01.