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39-529: The Rapid Rectilinear also named Aplanat is a famous photographic lens design. The Rapid Rectilinear is a lens that is symmetrical about its aperture stop with four elements in two groups. It was introduced by John Henry Dallmeyer in 1866. The symmetry of the design greatly reduces radial distortion , improving on the Petzval lens . This photography-related article is a stub . You can help Misplaced Pages by expanding it . Photographic lens There

78-475: A UV coating to keep out the ultraviolet light that could taint color. Most modern optical cements for bonding glass elements also block UV light, negating the need for a UV filter. However, this leaves an avenue for lens fungus to attack if lenses are not cared for appropriately. UV photographers must go to great lengths to find lenses with no cement or coatings. A lens will most often have an aperture adjustment mechanism, usually an iris diaphragm , to regulate

117-435: A compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these and produce a design that is suitable for photographic use and possibly mass production. Typical rectilinear lenses can be thought of as "improved" pinhole "lenses" . As shown,

156-406: A doublet (two elements) will often suffice. Some older cameras were fitted with convertible lenses (German: Satzobjektiv ) of normal focal length. The front element could be unscrewed, leaving a lens of twice the focal length, and half the angle of view and half the aperture. The simpler half-lens was of adequate quality for the narrow angle of view and small relative aperture. This would require

195-599: A floating system; and Hasselblad and Mamiya call it FLE (floating lens element). Glass is the most common material used to construct lens elements, due to its good optical properties and resistance to scratching. Other materials are also used, such as quartz glass , fluorite , plastics like acrylic (Plexiglass), and even germanium and meteoritic glass . Plastics allow the manufacturing of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacturing and performance. Plastics are not used for

234-400: A pinhole "lens" is simply a small aperture that blocks most rays of light, ideally selecting one ray to the object for each point on the image sensor. Pinhole lenses have a few severe limitations: Practical lenses can be thought of as an answer to the question: "how can a pinhole lens be modified to admit more light and give a smaller spot size?". A first step is to put a simple convex lens at

273-436: A simple pinhole lens, but rather than being illuminated by single rays of light, each image point is illuminated by a focused "pencil" of light rays . From the front of the camera, the small hole (the aperture), would be seen. The virtual image of the aperture as seen from the world is known as the lens's entrance pupil ; ideally, all rays of light leaving a point on the object that enter the entrance pupil will be focused to

312-543: A surface with a light source, such as the Earth 's surface and the Sun . It can also be equivalently described as the angle between the tangent plane of the surface and another plane at right angles to the light rays. This means that the illumination angle of a certain point on Earth's surface is 0° if the Sun is precisely overhead and that it is 90° at sunset or sunrise . Determining

351-412: A wider field of view than longer focal length lenses. A wider aperture, identified by a smaller f-number, allows using a faster shutter speed for the same exposure. The camera equation , or G#, is the ratio of the radiance reaching the camera sensor to the irradiance on the focal plane of the camera lens. The maximum usable aperture of a lens is specified as the focal ratio or f-number , defined as

390-612: Is believed to be the Carl Zeiss Planar 50mm f/0.7 , which was designed and made specifically for the NASA Apollo lunar program to capture the far side of the Moon in 1966. Three of these lenses were purchased by filmmaker Stanley Kubrick in order to film scenes in his 1975 film Barry Lyndon , using candlelight as the sole light source. The complexity of a lens — the number of elements and their degree of asphericity — depends upon

429-439: Is generally used to image close-up very small subjects. A macro lens may be of any focal length, the actual focus length being determined by its practical use, considering magnification, the required ratio, access to the subject, and illumination considerations. It can be a special lens corrected optically for close up work or it can be any lens modified (with adapters or spacers, which are also known as "extension tubes".) to bring

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468-431: Is no major difference in principle between a lens used for a still camera , a video camera , a telescope , a microscope , or other apparatus, but the details of design and construction are different. A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths , apertures , and other properties. While in principle a simple convex lens will suffice, in practice

507-566: Is not true that all lenses with plastic elements are of low photographic quality. The 1951 USAF resolution test chart is one way to measure the resolving power of a lens. The quality of the material, coatings, and build affect the resolution. Lens resolution is ultimately limited by diffraction , and very few photographic lenses approach this resolution. Ones that do are called "diffraction limited" and are usually extremely expensive. Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. Some lenses have

546-405: Is the different distances from which a subject can be framed, resulting in a different perspective . Photographs can be taken of a person stretching out a hand with a wideangle, a normal lens, and a telephoto, which contain exactly the same image size by changing the distance from the subject. But the perspective will be different. With the wideangle, the hands will be exaggeratedly large relative to

585-464: The Box Brownie 's meniscus lens, to over 20 in the more complex zooms. These elements may themselves comprise a group of lenses cemented together. The front element is critical to the performance of the whole assembly. In all modern lenses the surface is coated to reduce abrasion, flare , and surface reflectance , and to adjust color balance. To minimize aberration, the curvature is usually set so that

624-538: The Pentax K mount are found across multiple brands, but this is not common today. A few mount designs, such as the Olympus/Kodak Four Thirds System mount for DSLRs, have also been licensed to other makers. Most large-format cameras take interchangeable lenses as well, which are usually mounted in a lensboard or on the front standard. The most common interchangeable lens mounts on the market today include

663-513: The angle of incidence and the angle of refraction are equal. In a prime lens this is easy, but in a zoom there is always a compromise. The lens usually is focused by adjusting the distance from the lens assembly to the image plane, or by moving elements of the lens assembly. To improve performance, some lenses have a cam system that adjusts the distance between the groups as the lens is focused. Manufacturers call this different things: Nikon calls it CRC (close range correction); Canon calls it

702-511: The bellows had to be extended to twice the normal length. Good-quality lenses with maximum aperture no greater than f/2.8 and fixed, normal, focal length need at least three (triplet) or four elements (the trade name " Tessar " derives from the Greek tessera , meaning "four"). The widest-range zooms often have fifteen or more. The reflection of light at each of the many interfaces between different optical media (air, glass, plastic) seriously degraded

741-679: The contrast and color saturation of early lenses, particularly zoom lenses, especially where the lens was directly illuminated by a light source. The introduction many years ago of optical coatings, and advances in coating technology over the years, have resulted in major improvements, and modern high-quality zoom lenses give images of quite acceptable contrast, although zoom lenses with many elements will transmit less light than lenses made with fewer elements (all other factors such as aperture, focal length, and coatings being equal). Many single-lens reflex cameras and some rangefinder cameras have detachable lenses. A few other types do as well, notably

780-730: The Canon EF , EF-S and EF-M autofocus lens mounts. Others include the Nikon F manual and autofocus mounts, the Olympus / Kodak Four Thirds and Olympus/Panasonic Micro Four Thirds digital-only mounts, the Pentax K mount and autofocus variants, the Sony Alpha mount (derived from the Minolta mount) and the Sony E digital-only mount. A macro lens used in macro or "close-up" photography (not to be confused with

819-484: The Mamiya TLR cameras and SLR, medium format cameras ( RZ67 , RB67 , 645-1000s)other companies that produce medium format equipment such as Bronica, Hasselblad and Fuji have similar camera styles that allow interchangeability in the lenses as well, and mirrorless interchangeable-lens cameras . The lenses attach to the camera using a lens mount , which contains mechanical linkages and often also electrical contacts between

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858-425: The amount of light that passes. In early camera models a rotating plate or slider with different sized holes was used. These Waterhouse stops may still be found on modern, specialized lenses. A shutter , to regulate the time during which light may pass, may be incorporated within the lens assembly (for better quality imagery), within the camera, or even, rarely, in front of the lens. Some cameras with leaf shutters in

897-449: The angle of incidence is called the grazing angle or glancing angle . Incidence at small grazing angles is called "grazing incidence." Grazing incidence diffraction is used in X-ray spectroscopy and atom optics , where significant reflection can be achieved only at small values of the grazing angle. Ridged mirrors are designed to reflect atoms coming at a small grazing angle. This angle

936-402: The angle of reflection with respect to a planar surface is trivial, but the computation for almost any other surface is significantly more difficult. When dealing with a beam that is nearly parallel to a surface, it is sometimes more useful to refer to the angle between the beam and the surface tangent , rather than that between the beam and the surface normal . The 90-degree complement to

975-415: The angle of view, the maximum aperture, and intended price point, among other variables. An extreme wideangle lens of large aperture must be of very complex construction to correct for optical aberrations, which are worse at the edge of the field and when the edge of a large lens is used for image-forming. A long-focus lens of small aperture can be of very simple construction to attain comparable image quality:

1014-465: The aperture open until the instant of exposure to allow SLR cameras to focus with a brighter image with shallower depth of field, theoretically allowing better focus accuracy. Focal lengths are usually specified in millimetres (mm), but older lenses might be marked in centimetres (cm) or inches. For a given film or sensor size, specified by the length of the diagonal, a lens may be classified as a: A side effect of using lenses of different focal lengths

1053-436: The aperture, but in general these three will be in different places. Practical photographic lenses include more lens elements. The additional elements allow lens designers to reduce various aberrations, but the principle of operation remains the same: pencils of rays are collected at the entrance pupil and focused down from the exit pupil onto the image plane. A camera lens may be made from a number of elements: from one, as in

1092-597: The barrel or pressing a button which activates an electric motor . Commonly, the lens may zoom from moderate wide-angle, through normal, to moderate telephoto; or from normal to extreme telephoto. The zoom range is limited by manufacturing constraints; the ideal of a lens of large maximum aperture which will zoom from extreme wideangle to extreme telephoto is not attainable. Zoom lenses are widely used for small-format cameras of all types: still and cine cameras with fixed or interchangeable lenses. Bulk and price limit their use for larger film sizes. Motorized zoom lenses may also have

1131-453: The compositional term close up ) is any lens that produces an image on the focal plane (i.e., film or a digital sensor) that is one quarter of life size (1:4) to the same size (1:1) as the subject being imaged. There is no official standard to define a macro lens, usually a prime lens , but a 1:1 ratio is, typically, considered "true" macro. Magnification from life size to larger is called "Micro" photography (2:1, 3:1 etc.). This configuration

1170-400: The figure below, the line representing a ray makes an angle θ with the normal (dotted line). The angle of incidence at which light is first totally internally reflected is known as the critical angle . The angle of reflection and angle of refraction are other angles related to beams. In computer graphics and geography , the angle of incidence is also known as the illumination angle of

1209-400: The focal plane "forward" for very close photography. Depending on the camera to subject distance and aperture, the depth-of-field can be very narrow, limiting the linear depth of the area that will be in focus. Lenses are usually stopped down to give a greater depth-of-field. Some lenses, called zoom lenses , have a focal length that varies as internal elements are moved, typically by rotating

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1248-447: The focus, iris, and other functions motorized. Some notable photographic optical lens designs are: Angle of incidence (optics) The angle of incidence , in geometric optics , is the angle between a ray incident on a surface and the line perpendicular (at 90 degree angle) to the surface at the point of incidence, called the normal . The ray can be formed by any waves, such as optical , acoustic , microwave , and X-ray . In

1287-479: The head. As the focal length increases, the emphasis on the outstretched hand decreases. However, if pictures are taken from the same distance, and enlarged and cropped to contain the same view, the pictures will have identical perspective. A moderate long-focus (telephoto) lens is often recommended for portraiture because the perspective corresponding to the longer shooting distance is considered to look more flattering. The widest aperture lens in history of photography

1326-456: The lens and camera body. The lens mount design is an important issue for compatibility between cameras and lenses. There is no universal standard for lens mounts, and each major camera maker typically uses its own proprietary design, incompatible with other makers. A few older manual focus lens mount designs, such as the Leica M39 lens mount for rangefinders, M42 lens mount for early SLRs, and

1365-421: The lens omit the aperture, and the shutter does double duty. The two fundamental parameters of an optical lens are the focal length and the maximum aperture . The lens' focal length determines the magnification of the image projected onto the image plane, and the aperture the light intensity of that image. For a given photographic system the focal length determines the angle of view , short focal lengths giving

1404-459: The lens's focal length divided by the effective aperture (or entrance pupil ), a dimensionless number. The lower the f-number, the higher light intensity at the focal plane. Larger apertures (smaller f-numbers) provide a much shallower depth of field than smaller apertures, other conditions being equal. Practical lens assemblies may also contain mechanisms to deal with measuring light, secondary apertures for flare reduction, and mechanisms to hold

1443-424: The outermost elements of all but the cheapest lenses as they scratch easily. Molded plastic lenses have been used for the cheapest disposable cameras for many years, and have acquired a bad reputation: manufacturers of quality optics tend to use euphemisms such as "optical resin". However many modern, high performance (and high priced) lenses from popular manufacturers include molded or hybrid aspherical elements, so it

1482-411: The pinhole with a focal length equal to the distance to the film plane (assuming the camera will take pictures of distant objects ). This allows the pinhole to be opened up significantly (fourth image) because a thin convex lens bends light rays in proportion to their distance to the axis of the lens, with rays striking the center of the lens passing straight through. The geometry is almost the same as with

1521-400: The same point on the image sensor/film (provided the object point is in the field of view). If one were inside the camera, one would see the lens acting as a projector . The virtual image of the aperture from inside the camera is the lens's exit pupil . In this simple case, the aperture, entrance pupil, and exit pupil are all in the same place because the only optical element is in the plane of

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