1.
Optics
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Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light, because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for using the classical description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice, practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines, physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Historically, the model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that waves were in fact electromagnetic radiation. Some phenomena depend on the fact that light has both wave-like and particle-like properties, explanation of these effects requires quantum mechanics. When considering lights particle-like properties, the light is modelled as a collection of particles called photons, quantum optics deals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics. Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, the earliest known lenses, made from polished crystal, often quartz, date from as early as 700 BC for Assyrian lenses such as the Layard/Nimrud lens. The ancient Romans and Greeks filled glass spheres with water to make lenses, the word optics comes from the ancient Greek word ὀπτική, meaning appearance, look. Greek philosophy on optics broke down into two opposing theories on how vision worked, the theory and the emission theory. The intro-mission approach saw vision as coming from objects casting off copies of themselves that were captured by the eye, plato first articulated the emission theory, the idea that visual perception is accomplished by rays emitted by the eyes. He also commented on the parity reversal of mirrors in Timaeus, some hundred years later, Euclid wrote a treatise entitled Optics where he linked vision to geometry, creating geometrical optics. Ptolemy, in his treatise Optics, held a theory of vision, the rays from the eye formed a cone, the vertex being within the eye. The rays were sensitive, and conveyed back to the observer’s intellect about the distance. He summarised much of Euclid and went on to describe a way to measure the angle of refraction, during the Middle Ages, Greek ideas about optics were resurrected and extended by writers in the Muslim world
2.
Light
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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to light, which is visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m. This wavelength means a range of roughly 430–750 terahertz. The main source of light on Earth is the Sun, sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the used by living things. Historically, another important source of light for humans has been fire, with the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence, for example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey. Visible light, as all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term sometimes refers to electromagnetic radiation of any wavelength. In this sense, gamma rays, X-rays, microwaves and radio waves are also light, like all types of light, visible light is emitted and absorbed in tiny packets called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality, the study of light, known as optics, is an important research area in modern physics. Generally, EM radiation, or EMR, is classified by wavelength into radio, microwave, infrared, the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths, when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. There exist animals that are sensitive to various types of infrared, infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it, above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nanometers and the internal lens below 400. Furthermore, the rods and cones located in the retina of the eye cannot detect the very short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, various sources define visible light as narrowly as 420 to 680 to as broadly as 380 to 800 nm
3.
Photography
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Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. With an electronic sensor, this produces an electrical charge at each pixel. A negative image on film is used to photographically create a positive image on a paper base, known as a print. The word photography was created from the Greek roots φωτός, genitive of φῶς, light and γραφή representation by means of lines or drawing, several people may have coined the same new term from these roots independently. Johann von Maedler, a Berlin astronomer, is credited in a 1932 German history of photography as having used it in an article published on 25 February 1839 in the German newspaper Vossische Zeitung. Both of these claims are now widely reported but apparently neither has ever been confirmed as beyond reasonable doubt. Credit has traditionally given to Sir John Herschel both for coining the word and for introducing it to the public. Photography is the result of combining several technical discoveries, later Greek mathematicians Aristotle and Euclid also independently described a pinhole camera in the 5th and 4th centuries BCE. Daniele Barbaro described a diaphragm in 1566, wilhelm Homberg described how light darkened some chemicals in 1694. The fiction book Giphantie, published in 1760, by French author Tiphaigne de la Roche, the discovery of the camera obscura that provides an image of a scene dates back to ancient China. Leonardo da Vinci mentions natural camera obscura that are formed by dark caves on the edge of a sunlit valley, a hole in the cave wall will act as a pinhole camera and project a laterally reversed, upside down image on a piece of paper. So the birth of photography was primarily concerned with inventing means to capture, renaissance painters used the camera obscura which, in fact, gives the optical rendering in color that dominates Western Art. The camera obscura literally means dark chamber in Latin and it is a box with a hole in it which allows light to go through and create an image onto the piece of paper. Around the year 1800, British inventor Thomas Wedgwood made the first known attempt to capture the image in a camera obscura by means of a light-sensitive substance and he used paper or white leather treated with silver nitrate. The shadow images eventually darkened all over, the first permanent photoetching was an image produced in 1822 by the French inventor Nicéphore Niépce, but it was destroyed in a later attempt to make prints from it. Niépce was successful again in 1825, in 1826 or 1827, he made the View from the Window at Le Gras, the earliest surviving photograph from nature. Because Niépces camera photographs required a long exposure, he sought to greatly improve his bitumen process or replace it with one that was more practical. With an eye to eventual commercial exploitation, the partners opted for total secrecy, Daguerres efforts culminated in what would later be named the daguerreotype process
4.
Angle of view
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In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the general term field of view. It is important to distinguish the angle of view from the angle of coverage, typically the image circle produced by a lens is large enough to cover the film or sensor completely, possibly including some vignetting toward the edge. A cameras angle of view not only on the lens. Digital sensors are usually smaller than 35mm film, and this causes the lens to have an angle of view than with 35mm film. In everyday digital cameras, the factor can range from around 1, to 1.6. For lenses projecting rectilinear images of distant objects, the focal length. Calculations for lenses producing non-rectilinear images are more complex and in the end not very useful in most practical applications. Angle of view may be measured horizontally, vertically, or diagonally, for example, for 35mm film which is 36 mm wide and 24mm high, d =36 mm would be used to obtain the horizontal angle of view and d =24 mm for the vertical angle. Because this is a function, the angle of view does not vary quite linearly with the reciprocal of the focal length. However, except for wide-angle lenses, it is reasonable to approximate α ≈ d f radians or 180 d π f degrees. The effective focal length is equal to the stated focal length of the lens. Angle of view can also be determined using FOV tables or paper or software lens calculators, consider a 35 mm camera with a lens having a focal length of F =50 mm. The dimensions of the 35 mm image format are 24 mm ×36 mm, here α is defined to be the angle-of-view, since it is the angle enclosing the largest object whose image can fit on the film. We want to find the relationship between, the angle α the opposite side of the triangle, d /2 the adjacent side, S2 Using basic trigonometry, we find. For macro photography, we neglect the difference between S2 and F. From the thin lens formula,1 F =1 S1 +1 S2, a second effect which comes into play in macro photography is lens asymmetry. The lens asymmetry causes an offset between the plane and pupil positions
5.
Microscopy
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Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye. There are three branches of microscopy, optical, electron, and scanning probe microscopy. This process may be carried out by irradiation of the sample or by scanning of a fine beam over the sample. Scanning probe microscopy involves the interaction of a probe with the surface of the object of interest. The development of microscopy revolutionized biology, gave rise to the field of histology and so remains an essential technique in the life and physical sciences. Optical or light microscopy involves passing visible light transmitted through or reflected from the sample through a single or multiple lenses to allow a view of the sample. The resulting image can be detected directly by the eye, imaged on a plate or captured digitally. The single lens with its attachments, or the system of lenses and imaging equipment, along with the lighting equipment, sample stage and support. The most recent development is the microscope, which uses a CCD camera to focus on the exhibit of interest. The image is shown on a screen, so eye-pieces are unnecessary. Limitations of standard optical microscopy lie in three areas, This technique can only image dark or strongly refracting objects effectively, diffraction limits resolution to approximately 0.2 micrometres. This limits the practical limit to ~1500x. Out of focus light from points outside the focal plane reduces image clarity, live cells in particular generally lack sufficient contrast to be studied successfully, since the internal structures of the cell are colourless and transparent. The most common way to increase contrast is to stain the different structures with selective dyes, staining may also introduce artifacts, apparent structural details that are caused by the processing of the specimen and are thus not legitimate features of the specimen. In general, these make use of differences in the refractive index of cell structures. It is comparable to looking through a window, you dont see the glass. There is a difference, as glass is a material. The human eye is not sensitive to this difference in phase, in order to improve specimen contrast or highlight certain structures in a sample special techniques must be used
6.
Telescope
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A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation. The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s and they found use in both terrestrial applications and astronomy. Within a few decades, the telescope was invented, which used mirrors to collect. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galileis instruments presented at a banquet at the Accademia dei Lincei, in the Starry Messenger, Galileo had used the term perspicillum. The earliest recorded working telescopes were the telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals, Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year. Also in 1609, Thomas Harriot became the first person known to point a telescope skyward in order to make observations of a celestial object. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs, in 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector. The invention of the lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter. The largest reflecting telescopes currently have objectives larger than 10 m, the 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937, since then, a tremendous variety of complex astronomical instruments have been developed. The name telescope covers a range of instruments. Most detect electromagnetic radiation, but there are differences in how astronomers must go about collecting light in different frequency bands. The near-infrared can be collected much like light, however in the far-infrared and submillimetre range. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, on the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the range from about 0.2 μm to 1.7 μm
7.
Mirror
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This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light. The most familiar type of mirror is the mirror, which has a flat screen surface. Curved mirrors are used, to produce magnified or diminished images or focus light or simply distort the reflected image. Mirrors are commonly used for personal grooming or admiring oneself, decoration, Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for light, however, mirrors designed for other wavelengths of electromagnetic radiation are also used. The first mirrors used by people were most likely pools of dark, still water, the requirements for making a good mirror are a surface with a very high degree of flatness, and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as obsidian, examples of obsidian mirrors found in Anatolia have been dated to around 6000 BC. Mirrors of polished copper were crafted in Mesopotamia from 4000 BC, polished stone mirrors from Central and South America date from around 2000 BC onwards. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze, Mirrors made of other metal mixtures such as copper and tin speculum metal may have also been produced in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were owned by the wealthy. Stone mirrors often had poor reflectivity compared to metals, yet metals scratch or tarnish easily, depending upon the color, both often yielded reflections with poor color rendering. The poor image quality of ancient mirrors explains 1 Corinthians 13s reference to seeing as in a mirror, glass was a desirable material for mirrors. Because the surface of glass is smooth, it produces reflections with very little blur. In addition, glass is very hard and scratch resistant, however, glass by itself has little reflectivity, so people began coating it with metals to increase the reflectivity. According to Pliny, the people of Sidon developed a technique for creating crude mirrors by coating glass with molten lead. Glass mirrors backed with gold leaf are mentioned by Pliny in his Natural History and these circular mirrors were typically small, from only a fraction of an inch to as much as eight inches in diameter. These small mirrors produced distorted images, yet were prized objects of high value and these ancient glass mirrors were very thin, thus very fragile, because the glass needed to be extremely thin to prevent cracking when coated with a hot, molten metal. Due to the quality, high cost, and small size of these ancient glass mirrors
8.
Curved mirror
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A curved mirror is a mirror with a curved reflecting surface. The surface may be convex or concave. Most curved mirrors have surfaces that are shaped like part of a sphere, one advantage that mirror optics have over lens optics is that mirrors do not introduce chromatic aberration. A convex mirror, fish eye mirror or diverging mirror, is a mirror in which the reflective surface bulges toward the light source. Convex mirrors reflect light outwards, therefore they are not used to focus light, such mirrors always form a virtual image, since the focal point and the centre of curvature are both imaginary points inside the mirror, that cannot be reached. As a result, images formed by these mirrors cannot be projected on a screen, the image is smaller than the object, but gets larger as the object approaches the mirror. A collimated beam of light diverges after reflection from a convex mirror, the passenger-side mirror on a car is typically a convex mirror. In some countries, these are labeled with the safety warning Objects in mirror are closer than they appear, convex mirrors are preferred in vehicles because they give an upright, though diminished, image. Also they provide a field of view as they are curved outwards. These mirrors are often found in the hallways of buildings, including hospitals, hotels, schools, stores. They are usually mounted on a wall or ceiling where hallways intersect each other and they are useful for people accessing the hallways, especially at locations having blind spots or where visibility may be limited. They are also used on roads, driveways, and alleys to provide safety for motorists where there is a lack of visibility, especially at curves and turns. Convex mirrors are used in automated teller machines as a simple and handy security feature. Similar devices are sold to be attached to ordinary computer monitors, convex mirrors make everything seem smaller but cover a larger area of surveillance. Round convex mirrors called Oeil de Sorcière were a luxury item from the 15th century onwards. With 15th century technology, it was easier to make a curved mirror than a perfectly flat one. They were also known as bankers eyes due to the fact that their field of vision was useful for security. Famous examples in art include the Arnolfini Portrait by Jan van Eyck, the image on a convex mirror is always virtual, diminished, and upright
9.
135 film
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135 is photographic film in a film format used for still photography. It is a film with a film gauge of 35 mm. Its engineering standard for the film is controlled by ISO1007, the term 135 was introduced by Kodak in 1934 as a designation for the cassette for 35 mm film, specifically for still photography. It quickly grew in popularity, surpassing 120 film by the late 1960s to become the most popular photographic film size, despite competition from formats such as 828,126,110, and APS, it remains so today. 135 camera film always comes perforated with Kodak Standard perforations, the size of the 135 film frame has been adopted by many high-end digital single-lens reflex and digital mirrorless cameras, commonly referred to as full frame. Even though the format is smaller than historical medium format and large format film, it is much larger than image sensors in most compact cameras. Individual rolls of 135 film are enclosed in single-spool, light-tight, the film is clipped or taped to a spool and exits via a slot lined with flocking. The end of the film is cut on one side to form a leader and it has the same dimensions and perforation pitch as 35 mm movie print film. Most cameras require the film to be rewound before the camera is opened, disposable cameras use the same technique so that the user does not have to rewind. Since the 1980s film cassettes have been marked with a DX encoding pattern, conforming cameras detect this, different films are sensitive to light at different degrees, this film speed is standardised by ISO.135 film has been made in several emulsion types and sensitivities. Since the introduction of digital cameras the most usual films have colour emulsions of ISO 100/21° to ISO 800/30°, films of lower sensitivity and higher sensitivity are for more specialist purposes. There are colour and monochrome films, negative and positive, monochrome film is usually panchromatic, orthochromatic has fallen out of use. Film designed to be sensitive to infrared radiation can be obtained, more exotic emulsions have been available in 135 than other roll-film sizes. The term 135 format usually refers to a 36×24 mm film format, the 36×24 mm format is common to digital image sensors, where it is typically referred to as full frame format. On 135 film, the dimension of the 36×24 mm frame runs parallel to the length of the film. The perforation size and pitch are according to the standard specification KS-1870, for each frame, the film advances 8 perforations. This is specified as 38.00 mm and this allows for 2 mm gaps between frames. Each camera model has a different location for the sprocket which advances the film, therefore, each camera model’s frame will vary in position relative to the perforations
10.
35 mm film
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35 mm film is the film gauge most commonly used for motion pictures and chemical still photography. The name of the gauge refers to the width of the photographic film, the standard negative pulldown for movies is four perforations per frame along both edges, which results in 16 frames per foot of film. For still photography, the frame has eight perforations on each side. This resulted in cameras, projectors, and other equipment having to be calibrated to each gauge, the 35 mm width, originally specified as 1.375 inches, was introduced in 1892 by William Dickson and Thomas Edison, using film stock supplied by George Eastman. The gauge has been versatile in application, Eastman Kodak, Fujifilm and Agfa-Gevaert are some companies which offered 35 mm films. Today Kodak is the last remaining manufacturer of motion picture film and it is difficult to compare the quality of film to digital media but a good estimate would be about 20.8 million total pixels would equal one 35 millimeter high quality color frame of film. In 1880, George Eastman began to manufacture gelatin dry plates in Rochester. Along with W. H. Walker, Eastman invented a holder for a roll of picture-carrying gelatin layer coated paper, hannibal Goodwins invention of nitrocellulose film base in 1887 was the first transparent, flexible film. With the advent of film, Thomas Alva Edison quickly set out on his invention, the Kinetoscope. The Kinetoscope was a loop system intended for one-person viewing. Edison, along with assistant W. K. L. Dickson, followed that up with the Kinetophone, beginning in March 1892, Eastman and then, from April 1893 into 1896, New Yorks Blair Camera Co. supplied Edison with film stock. Edisons aperture defined a single frame of film at 4 perforations high, a court judgment in March 1902 invalidated Edisons claim, allowing any producer or distributor to use the Edison 35 mm film design without license. Filmmakers were already doing so in Britain and Europe, where Edison had failed to file patents, at the time, film stock was usually supplied unperforated and punched by the filmmaker to their standards with perforation equipment. A variation developed by the Lumière Brothers used a circular perforation on each side of the frame towards the middle of the horizontal axis.33 aspect ratio. Spehr describes the importance of these developments, The early acceptance of 35 mm as a standard had momentous impact on the development and spread of cinema. The film format was introduced into still photography as early as 1913 but first became popular with the launch of the Leica camera, created by Oskar Barnack in 1925. The costly image-forming silver compounds in a film stocks emulsion meant from the start that 35 mm filmmaking was to be a hobby with a high barrier to entry for the public at large. Furthermore, the film base of all early film stock was highly flammable
11.
Pinhole camera
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A pinhole camera is a simple camera without a lens but with a tiny aperture, a pinhole – effectively a light-proof box with a small hole in one side. Light from a scene passes through the aperture and projects an image on the opposite side of the box. It is based on property of light Camera obscura or pinhole images are an optical phenomenon. Early known descriptions are found in the Chinese Mozi writings and the Aristotelian Problems, starting with Alhazen the effect was used in dark rooms, mostly to study the nature of light and to safely watch sun eclipses. Giambattista della Porta wrote in 1558 in his Magia Naturalis about using a mirror to project the image onto paper. However, about the time the use of a lens instead of a pinhole was introduced. In the 17th century the camera obscura with a lens became a drawing aid that was further developed into a mobile device, first in a little tent. The photographic camera, as developed early in the 19th century, was basically, one older use of the term pin-hole in the context of optics was found in James Fergusons 1764 book Lectures on select subjects in mechanics, hydrostatics, pneumatics, and optics. Sir William Crookes and William de Wiveleslie Abney were other photographers to try the pinhole technique. The image of a camera may be projected onto a translucent screen for real-time viewing or to trace the image on paper. But it is often used without a translucent screen for pinhole photography with photographic film or photographic paper placed on the surface opposite to the pinhole aperture. A common use of photography is to capture the movement of the sun over a long period of time. This type of photography is called solargraphy, pinhole photography is used for artistic reasons, but also for educational purposes to let pupils learn about, and experiment with, the basics of photography. Pinhole cameras with CCDs are sometimes used for surveillance because they are difficult to detect, related cameras, image forming devices, or developments from it include Frankes widefield pinhole camera, the pinspeck camera, and the pinhead mirror. Pinhole photographs have nearly infinite depth of field, everything appears in focus, as theres no lens distortion, wide angle images remain absolutely rectilinear. Exposure times are long, resulting in motion blur around moving objects. Pinhole cameras can be handmade by the photographer for a particular purpose, in its simplest form, the photographic pinhole camera can consist of a light-tight box with a pinhole in one end, and a piece of film or photographic paper wedged or taped into the other end. A flap of cardboard with a hinge can be used as a shutter
12.
Telephoto lens
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In photography and cinematography, a telephoto lens is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length. This is achieved by incorporating a special group known as a telephoto group that extends the light path to create a long-focus lens in a much shorter overall design. The angle of view and other effects of long-focus lenses are the same for telephoto lenses of the same specified focal length, long-focal-length lenses are often informally referred to as telephoto lenses although this is technically incorrect, a telephoto lens specifically incorporates the telephoto group. In contrast to a lens, for any given focal length a simple lens of non-telephoto design is constructed from one lens. To focus on an object at infinity, the distance from this single lens to focal plane of the camera has to be adjusted to this focal length, for example, given a focal length of 500 mm, the distance between lens and focal plane is 500 mm. The farther the focal length is increased, the more the length of such a simple lens makes it unwieldy. But such simple lenses are not telephoto lenses, no matter how extreme the focal length – they are known as long-focus lenses, while the optical centre of a simple lens is within the construction, the telephoto lens moves the optical centre in front of the construction. The basic construction of a telephoto lens consists of front lens elements that, the focal length of this group is shorter than the effective focal length of the lens. The converging rays from this group are intercepted by the rear lens group, sometimes called the telephoto group, the simplest telephoto designs could consist of one element in each group, but in practice, more than one element is used in each group to correct for various aberrations. The combination of two groups produces a lens assembly that is physically shorter than a long-focus lens producing the same image size. This same property is achieved in camera lenses that combine mirrors with lenses and these designs, called catadioptric, reflex, or mirror lenses, have a curved mirror as the primary objective with some form of negative lens in front of the mirror to correct optical aberrations. They also use a secondary mirror to relay the image that extends the light cone the same way the negative lens telephoto group does. The mirrors also fold the light path, the heaviest non-Catadioptric telephoto lens for civilian use was made by Carl Zeiss and has a focal length of 1700 mm with a maximum aperture of f/4, implying a 425 mm entrance pupil. It is designed for use with a medium format Hasselblad 203 FE camera, the telephoto lens design has also been used for wide angles, at least once in the case of the Olympus XA where it permitted a 35mm focal length to fit in an extra compact camera body. Inverting the telephoto configuration, employing one or more negative lens groups in front of a positive lens group and this allows for greater clearance for other optical or mechanical parts such as the mirror parts in a single-lens reflex camera. Zoom lenses that are telephotos at one extreme of the zoom range, the concept of the telephoto lens, in reflecting form, was first described by Johannes Kepler in his Dioptrice of 1611, and re-invented by Peter Barlow in 1834. Some of his photographs are preserved in the holdings of the Turnbull Library in Wellington, one of McKay’s photographs shows the Russian warship Vjestnik anchored in Wellington harbour about two and a half kilometres away, with its rigging lines and gun ports clearly visible. The other, taken from the point, is of a local hotel
