NationMaster - Encyclopedia: Photographic lens

A photographic lens (or more correctly, objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically. Image File history File links Download high resolution version (1200x945, 274 KB) Lens Nikkor 18-70mm This image shows a Nikon Nikkor 18-70 AF-S DX / 3. ... Image File history File links Download high resolution version (1200x945, 274 KB) Lens Nikkor 18-70mm This image shows a Nikon Nikkor 18-70 AF-S DX / 3. ... Image File history File links Download high resolution version (1600x1067, 137 KB) Canon 17-40 F/4 L File links The following pages link to this file: Photographic lens Canon EF 17-40mm lens Category: ... Image File history File links Download high resolution version (1600x1067, 137 KB) Canon 17-40 F/4 L File links The following pages link to this file: Photographic lens Canon EF 17-40mm lens Category: ... ImageMetadata File history File links Download high resolution version (2047x1212, 905 KB) Despite the title this is a zoom, not a telephoto. ... ImageMetadata File history File links Download high resolution version (2047x1212, 905 KB) Despite the title this is a zoom, not a telephoto. ... A Canon Inc. ... The Canon Elph is a small digital camera with a durable steel case. ... Table of Opticks, 1728 Cyclopaedia Optics (appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... A lens. ... A camera is a device used to take pictures (usually photographs), either singly or in sequence, with or without sound recording, such as with video cameras. ... Undeveloped Arista black and white film, ISO 125. ...

While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct the many optical aberrations that arise. Convex lens converging light rays A convex lens, or converging lens, is a lens that is curved outward (convex): the ends are narrow and the middle is wide. ... A lens. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

There is no difference in principle between a lens used for a camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different. 50 cm refracting telescope at Nice Observatory. ... It has been suggested that microscopy be merged into this article or section. ...

A lens may be permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths and other properties. The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ...

A practical camera lens will often incorporate an aperture adjustment mechanism, often an iris diaphragm, to regulate the amount of light that may pass. A shutter, to regulate the time during which light may pass, may be incorporated within the lens assembly, or may be within the camera, or even, rarely, in front of the lens. In optics, an aperture is something which restricts the diameter of the light path through one plane in an optical system. ... A 35mm lens set to f/8; the diameter of the heptagonal diaphragm opening is 4. ... A shutter is a movable cover or screen that alternately prevents and permits the passage of some desirable (or undesirable) element. ...

The lens may usually be focused by adjusting the distance from the lens assembly to the image-forming surface, or by moving elements within the lens assembly. The focus or image point is the point where light rays, originating from a point in the object, converge [1]. The principal focus or focal point of a lens or parabolic mirror is the point onto which collimated light parallel to the axis is focused. ...

The lens elements are made of transparent materials. Glass is the most widely used material due to its good optical properties and resistance to scratching. Various plastics, such as acrylic (or PMMA), the material of Plexiglas, can also be used. Plastics allow the manufacture of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacture and performance. Plastics are not used for the outermost elements of all but the cheapest lenses as they scratch easily. Moulded 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". This article refers to the material. ... The term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. ... Structure of methyl methacrylate Polymethyl methacrylate (PMMA) or poly(methyl 2-methylpropanoate) is the synthetic polymer of methyl methacrylate. ... An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder. ...

The maximum usable aperture of a lens is usually specified, as the focal ratio or f-number, which is equal to the focal length divided by the actual aperture diameter in the same units. The lower the number, the more light is admitted through the lens. Practical lens assemblies may also contain mechanisms to deal with measuring light, to hold the aperture open until the instant of exposure to allow SLR cameras to focus with a bright image, etc. A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ... A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ... The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ... The single-lens reflex (SLR) is a type of camera that uses a movable mirror placed between the lens and the film to project the image seen through the lens to a matte focusing screen. ...

The two main optical parameters of a photographic lens are the focal length and the maximum aperture. The focal length determines the angle of view, the size of the image relative to that of the object, and the perspective; the maximum aperture limits the brightness of the image and the fastest shutter speed usable. The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ... In photography, angle of view (also called Angle of Coverage or Field of View) is the amount of a given scene shown on film; that is, there is generally much more to a scene visible to humans than shows up in photos, and various lenses record different degrees of the... Perspective when used in the context of vision and visual perception refers to the way in which objects appear to the eye based on their spatial attributes or dimension and the position of the eye relative to the objects. ...

Focal lengths are usually specifed in millimeters (mm), but older lenses marked in centimeter (cm) and inches are still to be found. For a given film or sensor size, specifed by the length of the diagonal, a lens may be classified as A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... The metre, or meter (symbol: m) is the SI base unit of length. ... Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ...

The 35mm film format is so prevalent that a 90mm lens, for example, is always assumed to be a moderate telephoto; but for the 7x5cm format it is normal, while on the large 5x4 inch format it is a wide-angle. In photography and cinematography a normal lens is a lens that generates images that are generally held to have a natural perspective compared with lenses with longer or shorter focal lengths. ... In photography and cinematography, a wide-angle lens is a lens whose focal length is shorter than the focal length of a normal lens. ... In photography and cinematography, a telephoto lens is a lens whose focal length is significantly longer than the focal length of a normal lens. ...

The real difference between lenses of different focal length is not the image size, but the perspective. You can take photographs 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 your distance from the subject. But the perspective will be different. With the wideangle, the hand will be exaggeratedly large relative to the head; as the focal length increases, the emphasis on the outstretched hand decreases. However, if you take pictures from the same distance, and enlarge and crop them to contain the same view, the pictures will be truly identical. A moderate long-focus (telephoto) lens is often recommended for portraiture because the flatter perspective is considered to look more realistic.

Some lenses, called zoom lenses, have a focal length which varies as internal elements are moved, typically by rotating the barrel or pressing a button which activates an electric motor. 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. A Canon Inc. ... Electric motors of various sizes. ...

The complexity of a lens—the number of elements and their degree of asphericity—depends upon the angle of view and the maximum aperture. 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; a doublet (with two elements) will often suffice. Some older cameras were fitted with "convertible" lenses of normal focal length; the front element could be unscrewed, leaving a lens of twice the focal length and 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. Obviously the bellows had to extend to twice the normal length. Hand bellows The bellows is a device for delivering pressured air in a controlled quantity to a controlled location. ...

Good-quality lenses with maximum aperture no greater than f/2.8 and fixed, normal, focal length need 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 the contrast and color saturation of early lenses, zoom lenses in particular, 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. Contrast has several meanings: // Visual perception In visual perception, contrast is the difference in visual properties that makes an object (or its representation in an image) distinguishable from other objects and the background. ... In color theory, saturation refers to the intensity of a specific hue. ... An optical coating is a thin layer of material placed on an optical component such as a lens or mirror which alters the way in which the optic reflects and transmits light. ...

Special purpose photographic lenses

Process and apochromat lenses are normally of small aperture, and are used for extremely accurate photographs of static objects. Colony of aphids on a stem. ... An apochromat, or apo lens, is a photographic or other lens that has a high degree of color correction. ... Chromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. ... Pincushion Simulation Pincushion distortion is a divergence from the rectilinear projection in geometric optics where image magnification increases with increasing distance from the optical axis. ... Barrel Simulation Barrel distortion is a divergence from the rectilinear projection in geometric optics where image magnification decreases with increasing distance from the optical axis. ...

A photographic enlarger is used in the dark room to project an image from a negative onto photographic paper. ... The Georgian terrace of Royal Crescent (Bath, England) from a hot air balloon Dulles Airport in Reston, Virginia, from an airplane Aerial photography is the taking of photographs from above with a camera mounted on an aircraft, balloon, rocket, kite, skydiver or similar vehicle. ... Fisheye 15mm (type: equisolid angle), 35mm-film, cropped by slide-frame. ...

Notable photographic optical lens designs

Some lens manufacturers (2006): The Retrofocus photographic lens was invented in France in 1950 by Angenieux, and is characterized by a large negative meniscus lens element up front followed by four or five small elements in the rear. ... The Cooke triplet is a photographic lens design designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by Cooke of York. ... The Double-Gauss design form has dominated the class of photographic lenses for many years. ... The Zeiss Tessar is a famous photographic lens design conceived by Paul Rudolph in 1902. ...

Canon Inc. ... Cosina Co. ... Konica Minolta (ã‚³ãƒ‹ã‚«ãƒŸãƒŽãƒ«ã‚¿) is a Japanese worldwide manufacturer of cameras, camera accessories, photo-copiers, fax machines and laser printers formed by a merger between Japanese imaging firms Konica and Minolta announced on January 7, 2003. ... Leica is a camera produced by a German company of the same name. ... Minolta was a Japanese worldwide manufacturer of cameras, camera accessories, photo-copiers, fax machines and laser printers. ... Nikon redirects here; there is also a leader of the Russian Orthodox Church named Patriarch Nikon. ... This article refers to a Japanese camera maker. ... // The Company PENTAX Corporation (ãƒšãƒ³ã‚¿ãƒƒã‚¯ã‚¹æ ªå¼ä¼šç¤¾) TYO: 7750 is a Japanese company founded in 1919 as æ—å…‰å¦å·¥æ¥åˆè³‡ä¼šç¤¾; Asahi KÅgaku KÅgyÅ GÅshi Gaisha, spectacle lens manufacturers. ... Tamron Co. ... Schneider Kreuznach is the abbreviated name of the Jos. ... Sigma Corporation is a Japanese company manufacturing cameras, lenses, flashes and other photographic accessories. ... Carl Zeiss The Carl Zeiss AG is a German manufacturer of optical systems, industrial measurements and medical devices, located in Oberkochen with important subsidiaries in Aalen and Jena. ...

Special purpose photographic lenses GA_googleFillSlot("encyclopedia_square");

Notable photographic optical lens designs

See also

Special purpose photographic lenses