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59-462: The body of the "periflex 1" is made of black painted metal alloy castings, while the top and base-plates are of black anodised stamped aluminium with delicate engravings. In later models the body covering material was brown pigskin, soon changed to black leather cloth because the pig skin stained easily. Also for this reason, whenever a camera was returned to the Wolverhampton works for service,

118-436: A dioptric telescope ). The refracting telescope design was originally used in spyglasses and astronomical telescopes but is also used for long-focus camera lenses . Although large refracting telescopes were very popular in the second half of the 19th century, for most research purposes, the refracting telescope has been superseded by the reflecting telescope , which allows larger apertures . A refractor's magnification

177-482: A focal point ; while those not parallel converge upon a focal plane . The telescope converts a bundle of parallel rays to make an angle α, with the optical axis to a second parallel bundle with angle β. The ratio β/α is called the angular magnification. It equals the ratio between the retinal image sizes obtained with and without the telescope. Refracting telescopes can come in many different configurations to correct for image orientation and types of aberration. Because

236-442: A waist-level viewfinder. Single-lens reflex (SLR) cameras use the camera lens itself, to completely eliminate parallax , the significant field-of-view error for close subjects caused by the offset distance between the viewfinder's lens and the camera's lens. Early SLRs were plate cameras , with a mechanism to insert a mirror between the lens and the film which reflected the light upwards, where it could be seen at waist level on

295-488: A bright aluminium barrel. Corfield had the British Optical Lens Company calculate the three element Cooke design, and subsequently became the manufacturer and supplier of the coated glass elements, while Corfield turned, cut and milled the barrels, and completed the lenses in their premises. Some time after that the engraving of the top plate was dropped and instead an engraved disc was placed under

354-430: A couple of years. Apochromatic refractors have objectives built with special, extra-low dispersion materials. They are designed to bring three wavelengths (typically red, green, and blue) into focus in the same plane. The residual color error (tertiary spectrum) can be an order of magnitude less than that of an achromatic lens. Such telescopes contain elements of fluorite or special, extra-low dispersion (ED) glass in

413-423: A digital accessory device used with digital cameras. These cameras had no separate viewfinder. The exact image (although upside-down and reversed left-right) was viewed on a ground glass installed either in a replaceable plateholder, or in a spring back where springs hold the ground glass at the focus plane until a photographic plateholder is slid in front of it. Spring backs usually had a flip-up cover protecting

472-435: A ground glass screen. When ready to take the picture, the mirror was pivoted out of the way (without moving the camera). Later SLR still cameras had a mechanism which flipped the mirror out of the way when the shutter button was pressed, opened and closed the shutter, and then moved the mirror back. The Zeiss Ikon Contax S was the first SLR camera to allow easy eye-level viewing by using a roof pentaprism to laterally reverse

531-540: A narrow field of view. Despite these flaws, the telescope was still good enough for Galileo to explore the sky. He used it to view craters on the Moon , the four largest moons of Jupiter , and the phases of Venus . Parallel rays of light from a distant object ( y ) would be brought to a focus in the focal plane of the objective lens ( F′ L1 / y′ ). The (diverging) eyepiece ( L2 ) lens intercepts these rays and renders them parallel once more. Non-parallel rays of light from

590-496: A non-inverted (i.e., upright) image. Galileo's most powerful telescope, with a total length of 980 millimeters (39 in; 3 ft 3 in; 1.07 yd; 98 cm; 9.8 dm; 0.98 m), magnified objects about 30 times. Galileo had to work with the poor lens technology of the time, and found he had to use aperture stops to reduce the diameter of the objective lens (increase its focal ratio ) to limit aberrations, so his telescope produced blurry and distorted images with

649-563: A refracting telescope is around 1 meter (39 in). There is a further problem of glass defects, striae or small air bubbles trapped within the glass. In addition, glass is opaque to certain wavelengths , and even visible light is dimmed by reflection and absorption when it crosses the air-glass interfaces and passes through the glass itself. Most of these problems are avoided or diminished in reflecting telescopes , which can be made in far larger apertures and which have all but replaced refractors for astronomical research. The ISS-WAC on

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708-410: A separate viewfinder. For those cameras, the electronic image is shown on a small accessory screen for composition and focusing purposes. CCTVs and webcams do not need any viewfinding device. Refracting telescope#Galilean telescope A refracting telescope (also called a refractor ) is a type of optical telescope that uses a lens as its objective to form an image (also referred to

767-480: Is a half mirror prism that reflect data from LCD to the optical viewfinder, so we can see both the shooting frame and the shooting data. A button can change the hybrid function to electronical viewfinder by blocking the image through the optical viewfinder with moving a half mirror prism to be a straight up mirror. Viewfinders are used for virtually all cameras whether still or movie, film, electronic analog (Television) or digital. Many digital sensor cameras do not have

826-404: Is an improvement on Galileo's design. It uses a convex lens as the eyepiece instead of Galileo's concave one. The advantage of this arrangement is that the rays of light emerging from the eyepiece are converging. This allows for a much wider field of view and greater eye relief , but the image for the viewer is inverted. Considerably higher magnifications can be reached with this design, but, like

885-570: Is calculated by dividing the focal length of the objective lens by that of the eyepiece . Refracting telescopes typically have a lens at the front, then a long tube , then an eyepiece or instrumentation at the rear, where the telescope view comes to focus. Originally, telescopes had an objective of one element, but a century later, two and even three element lenses were made. Refracting telescopes use technology that has often been applied to other optical devices, such as binoculars and zoom lenses / telephoto lens / long-focus lens . Refractors were

944-435: Is ground and polished , and then the two pieces are assembled together. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus in the same plane. Chester More Hall is noted as having made the first twin color corrected lens in 1730. Dollond achromats were quite popular in the 18th century. A major appeal was they could be made shorter. However, problems with glass making meant that

1003-427: Is likely to show considerable color fringing (generally a purple halo around bright objects); an f / 16 achromat has much less color fringing. In very large apertures, there is also a problem of lens sagging , a result of gravity deforming glass . Since a lens can only be held in place by its edge, the center of a large lens sags due to gravity, distorting the images it produces. The largest practical lens size in

1062-400: Is mounted in an accessory shoe slightly offset to the left-hand side on the top plate. It matches the field-of-view of the standard 50mm camera lens. It may be replaced by separately available ones matching the field of view of interchangeable lenses of the photographer's choice. The built-in focusing aide is situated centrally on the top plate. It is lowered manually into the light pass behind

1121-682: Is the Shuckburgh telescope (dating to the late 1700s). A famous refractor was the "Trophy Telescope", presented at the 1851 Great Exhibition in London. The era of the ' great refractors ' in the 19th century saw large achromatic lenses, culminating with the largest achromatic refractor ever built, the Great Paris Exhibition Telescope of 1900 . In the Royal Observatory, Greenwich an 1838 instrument named

1180-425: Is unlocked. The back comes off downwards as a single unit including the base-plate. The film-pressure plate of thick glass is mounted on a piece of rubber foam on the back. Inside the camera, on the left-hand side, is the 35mm film cassette chamber, and to the right is the counter clockwise rotating film take-up drum. It has a narrow slit for the film leader, and it rotates freely whenever the small film rewind button on

1239-477: Is viewed through a magnifying eyepiece, and due to a rubber eyepiece it can be viewed perfectly even in bright light. The second viewfinder would be larger, of a higher resolution, and may be mounted on the side of the camera. Because it consumes more power, a method is often provided to turn it off to save energy. In late 2010, Fujifilm announced hybrid viewfinder of optical viewfinder and electronic viewfinder in one viewfinder for its highend compact cameras . There

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1298-605: The Galilean satellites of Jupiter in 1610 with a refracting telescope. The planet Saturn's moon, Titan , was discovered on March 25, 1655, by the Dutch astronomer Christiaan Huygens . In 1861, the brightest star in the night sky, Sirius, was found to have smaller stellar companion using the 18 and half-inch Dearborn refracting telescope. By the 18th century refractors began to have major competition from reflectors, which could be made quite large and did not normally suffer from

1357-577: The Sheepshanks telescope includes an objective by Cauchoix. The Sheepshanks had a 6.7-inch (17 cm) wide lens, and was the biggest telescope at Greenwich for about twenty years. An 1840 report from the Observatory noted of the then-new Sheepshanks telescope with the Cauchoix doublet: The power and general goodness of this telescope make it a most welcome addition to the instruments of

1416-606: The Voyager 1 / 2 used a 6 centimetres (2.4 in) lens, launched into space in the late 1970s, an example of the use of refractors in space. Refracting telescopes were noted for their use in astronomy as well as for terrestrial viewing. Many early discoveries of the Solar System were made with singlet refractors. The use of refracting telescopic optics are ubiquitous in photography, and are also used in Earth orbit. One of

1475-458: The Galilean telescope, it still uses simple single element objective lens so needs to have a very high focal ratio to reduce aberrations ( Johannes Hevelius built an unwieldy f/225 telescope with a 200-millimetre (8 in) objective and a 46-metre (150 ft) focal length , and even longer tubeless " aerial telescopes " were constructed). The design also allows for use of a micrometer at

1534-473: The brown covering would be replaced without charge, if the owner so desired. A semiautomatic decrementing frame-counter is built into the wind-on knob visible through a small cutaway window in the knob. A small button next to it, which also doubles as a film rewind release, allows the wind-on knob to be turned back and forth to set the frame counter to the number of frames remaining on the loaded film. The optical viewfinder , with individual eyesight adjustment,

1593-455: The camera lens in the "Periflex 1" but in later models the fill wind-on mechanism also lowers the periscope. The cloth focal-plane shutter provides speeds from 1/30 to 1/1000 sec. and B. The shutter release button is situated on the right-hand camera front externally threaded for Leica cable release. The shutter control is the small milled knob on the top with numerals from 30 to 1000 and B engraved around it. It serves dual purposes, for winding

1652-591: The earliest type of optical telescope . The first record of a refracting telescope appeared in the Netherlands about 1608, when a spectacle maker from Middelburg named Hans Lippershey unsuccessfully tried to patent one. News of the patent spread fast and Galileo Galilei , happening to be in Venice in the month of May 1609, heard of the invention, constructed a version of his own , and applied it to making astronomical discoveries. All refracting telescopes use

1711-518: The economy model Periflex 2. British Optical Lens Company by David Gardner: http://www.gbcameras.org.uk/VP%20Twin/Company%20History.htm Viewfinder In photography, a viewfinder is a device on a camera that a photographer uses to determine exactly where the camera is pointed, and approximately how much of that view will be photographed. A viewfinder can be mechanical (indicating only direction and approximate view), with simple optical components, with precision optics and optical functions, or

1770-640: The famous triplet objectives is the Cooke triplet , noted for being able to correct the Seidal aberrations. It is recognized as one of the most important objective designs in the field of photography. The Cooke triplet can correct, with only three elements, for one wavelength, spherical aberration , coma , astigmatism , field curvature , and distortion . Refractors suffer from residual chromatic and spherical aberration . This affects shorter focal ratios more than longer ones. An f /6 achromatic refractor

1829-436: The focal plane (to determine the angular size and/or distance between objects observed). Huygens built an aerial telescope for Royal Society of London with a 19 cm (7.5″) single-element lens. The next major step in the evolution of refracting telescopes was the invention of the achromatic lens , a lens with multiple elements that helped solve problems with chromatic aberration and allowed shorter focal lengths. It

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1888-578: The glass objectives were not made more than about four inches (10 cm) in diameter. In the late 19th century, the Swiss optician Pierre-Louis Guinand developed a way to make higher quality glass blanks of greater than four inches (10 cm). He passed this technology to his apprentice Joseph von Fraunhofer , who further developed this technology and also developed the Fraunhofer doublet lens design. The breakthrough in glass making techniques led to

1947-578: The great refractors of the 19th century, that became progressively larger through the decade, eventually reaching over 1 meter by the end of that century before being superseded by silvered-glass reflecting telescopes in astronomy. Noted lens makers of the 19th century include: Some famous 19th century doublet refractors are the James Lick telescope (91 cm/36 in) and the Greenwich 28 inch refractor (71 cm). An example of an older refractor

2006-417: The ground glass. A black focusing cloth was used with larger models. Later referred to as "sports finders", for many sports and newspaper applications optical viewfinders gave too small an image and were inconvenient to use for scenes that were changing rapidly. For these purposes a simple arrangement of two wire rectangles, a smaller one nearer the eye and a larger one further away, was used, without optics;

2065-423: The image was formed by the bending of light, or refraction, these telescopes are called refracting telescopes or refractors . The design Galileo Galilei used c.  1609 is commonly called a Galilean telescope . It used a convergent (plano-convex) objective lens and a divergent (plano-concave) eyepiece lens (Galileo, 1610). A Galilean telescope, because the design has no intermediary focus, results in

2124-555: The inverted camera image (the reflex mirror had already vertically reversed the image). SLR movie cameras used a beamsplitter partial mirror to split the camera image between the shutter and film, and the viewfinder. A major advantage of SLR viewfinders is that any change of camera lens did not affect the viewing accuracy, and accurate camera focus did not depend on correct linking or calibration. Some sophisticated 20th century cameras with direct viewfinders had coincidence (split-image) rangefinders , initially with separate windows from

2183-408: The more famous applications of the refracting telescope was when Galileo used it to discover the four largest moons of Jupiter in 1609. Furthermore, early refractors were also used several decades later to discover Titan, the largest moon of Saturn, along with three more of Saturn's moons. In the 19th century, refracting telescopes were used for pioneering work on astrophotography and spectroscopy, and

2242-450: The object traveling at an angle α1 to the optical axis travel at a larger angle ( α2 > α1 ) after they passed through the eyepiece. This leads to an increase in the apparent angular size and is responsible for the perceived magnification. The final image ( y″ ) is a virtual image, located at infinity and is the same way up (i.e., non-inverted or upright) as the object. The Keplerian telescope , invented by Johannes Kepler in 1611,

2301-433: The objective and produce a very crisp image that is virtually free of chromatic aberration. Due to the special materials needed in the fabrication, apochromatic refractors are usually more expensive than telescopes of other types with a comparable aperture. In the 18th century, Dollond, a popular maker of doublet telescopes, also made a triplet, although they were not really as popular as the two element telescopes. One of

2360-470: The observatory In the 1900s a noted optics maker was Zeiss. An example of prime achievements of refractors, over 7 million people have been able to view through the 12-inch Zeiss refractor at Griffith Observatory since its opening in 1935; this is the most people to have viewed through any telescope. Achromats were popular in astronomy for making star catalogs, and they required less maintenance than metal mirrors. Some famous discoveries using achromats are

2419-527: The planet Neptune and the Moons of Mars . The long achromats, despite having smaller aperture than the larger reflectors, were often favored for "prestige" observatories. In the late 18th century, every few years, a larger and longer refractor would debut. For example, the Nice Observatory debuted with 77-centimeter (30.31 in) refractor, the largest at the time, but was surpassed within only

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2478-430: The pre-1925 astronomical convention that began the day at noon, give the time of discovery as 11 August 14:40 and 17 August 16:06 Washington mean time respectively). The telescope used for the discovery was the 26-inch (66 cm) refractor (telescope with a lens) then located at Foggy Bottom . In 1893 the lens was remounted and put in a new dome, where it remains into the 21st century. Jupiter's moon Amalthea

2537-552: The refractors. Despite this, some discoveries include the Moons of Mars, a fifth Moon of Jupiter, and many double star discoveries including Sirius (the Dog star). Refractors were often used for positional astronomy, besides from the other uses in photography and terrestrial viewing. The Galilean moons and many other moons of the solar system, were discovered with single-element objectives and aerial telescopes. Galileo Galilei 's discovered

2596-408: The related instrument, the heliometer, was used to calculate the distance to another star for the first time. Their modest apertures did not lead to as many discoveries and typically so small in aperture that many astronomical objects were simply not observable until the advent of long-exposure photography, by which time the reputation and quirks of reflecting telescopes were beginning to exceed those of

2655-405: The resolution of the photographer's eye ). Modern electronic viewfinders (EVF) are LCD or OLED based display devices. In addition to its primary purpose, an electronic viewfinder can be used to replay previously captured material, and as an on-screen display to browse through menus. A still camera's optical viewfinder typically has one or more small supplementary LED displays surrounding

2714-610: The same inherent problem with chromatic aberration. Nevertheless, the astronomical community continued to use doublet refractors of modest aperture in comparison to modern instruments. Noted discoveries include the Moons of Mars and a fifth moon of Jupiter, Amalthea . Asaph Hall discovered Deimos on 12 August 1877 at about 07:48 UTC and Phobos on 18 August 1877, at the US Naval Observatory in Washington, D.C. , at about 09:14 GMT (contemporary sources, using

2773-411: The same principles. The combination of an objective lens 1 and some type of eyepiece 2 is used to gather more light than the human eye is able to collect on its own, focus it 5 , and present the viewer with a brighter , clearer , and magnified virtual image 6 . The objective in a refracting telescope refracts or bends light . This refraction causes parallel light rays to converge at

2832-415: The shutter in a single anti-clockwise motion until a catch arrests it, and thence as a lift and turn type shutter speed selector. A standard coaxial flash synchronising socket is situated at the front of the camera, below the shutter release button. The camera back is removable for changing film. A milled button next to the tripod socket rotates either way to lock the back, while in a position in between it

2891-413: The shutter speed dial. "Corfield / Periflex / England" was engraved on the front of the periscope housing. After about one and a half year of manufacture, the top and base plate finish were changed to bright anodised aluminium. All later standard models were finished in bright aluminium and black leather. The Periflex was replaced by the largely reworked Periflex 3 in 1957, and a year later complemented by

2950-459: The side of folding cameras . These viewfinders were fitted to inexpensive cameras. Twin-lens reflex (TLR) cameras use a viewfinding lens with the same focal length as the camera lens, so it has the same field of view and focus properties. With a mirror, of similar size to the film, held at 45°, it projects an upright image onto a focusing ground glass screen viewable from above. The camera can be then be held steady at waist level. Although

3009-429: The top plate is depressed. No sprocket wheel is employed; instead, the film is pulled by, and wound onto the drum that always rotates the same angular amount for next picture frame. Acceptable frame spacing is accomplished by the large diameter take-up spool that reduces the effect of increasing spool diameter as more film is wound onto it. The Periflex was sold with a Corfield England Lumar f=50mm 1:3.5 standard lens in

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3068-510: The two rectangles were aligned so the smaller one was centered in the larger, and the larger rectangle would give an indication of what would be included. Cameras with sportsfinders usually had optical viewfinders also. A single divergent (plano-concave) lens, in front of a frame, when close to the eye, acts as a viewfinder. Adding a convergent (plano-convex) lens makes a very short reversed Galilean (upright image) telescope . For movie camera or others with changeable lenses, outline marks on one of

3127-557: The view of the scene is often provided. It typically shows the location and state of the camera's provided auto-focus points. This overlay can also provide lines or a grid which assist in picture composition . It is not uncommon for a camera to have two viewfinders. For example, a digital still camera may have an optical viewfinder and an electronic one. The latter can be used to replay previously captured material, has an on-screen display , and can be switched off to save power. A camcorder may have two viewfinders, both electronic. The first

3186-406: The view of the scene. On a film camera, these displays show shooting information such as the shutter speed and aperture and, for autofocus cameras, provide an indication that the image is correctly focussed. Digital still cameras will typically also display information such as the current ISO setting and the number of remaining shots which can be taken in a burst. Another display which overlays

3245-629: The viewfinder lens was similar to the camera lens, the optical quality was less important and so the cost is reduced. TLR viewfinders do not have the interrupted viewing and shutter lag of the SLR type and so is preferred for dance photography. Reinhold Heidecke cited his experience with periscope focusing from the German trenches in 1916 as the inspiration for the Rolleiflex line in 1929. Some similar-looking cameras are actually simple box cameras with

3304-431: The viewfinder lenses could show the different fields of view for the different camera lenses. Simple reflecting viewfinders, known also as "brilliant finders", comprised a small forward-looking lens, a small mirror at 45° behind it, and a lens at the top; the user held the camera at waist level and looked down into the lens, where a small image could be seen. Such viewfinders were integrated into box cameras , and fitted to

3363-544: The viewfinder, later integrated with it; they were called rangefinder cameras . Cameras with interchangeable lenses had to indicate the field of view of each lens in the viewfinder; more usually, interchangeable viewfinders to match the lenses were used. Viewfinders can be optical or electronic . An optical viewfinder is simply a reversed telescope that displays what the camera sees. It has many drawbacks, but it also has advantages; it consumes no power, it does not wash out in sunlight, and it has "full resolution" (i.e.

3422-438: Was discovered on 9 September 1892, by Edward Emerson Barnard using the 36 inches (91 cm) refractor telescope at Lick Observatory . It was discovered by direct visual observation with the doublet-lens refractor. In 1904, one of the discoveries made using Great Refractor of Potsdam (a double telescope with two doublets) was of the interstellar medium . The astronomer Professor Hartmann determined from observations of

3481-423: Was invented in 1733 by an English barrister named Chester Moore Hall , although it was independently invented and patented by John Dollond around 1758. The design overcame the need for very long focal lengths in refracting telescopes by using an objective made of two pieces of glass with different dispersion , ' crown ' and ' flint glass ', to reduce chromatic and spherical aberration . Each side of each piece

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