A photographic lens (also known as objective lens or photographic 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. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging A camera is a device used to capture images either as still Photographs or as sequences of moving images ( Movies or Videos. This article is mainly concerned with Still photography film For Motion picture film please see Film stock.

Photographic lens: Nikon's AF-S DX Zoom-Nikkor 18–70 f/3. 5–4. 5G IF-ED zoom lens

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 (as much as possible) the many optical aberrations that arise. A zoom lens is a mechanical assembly of lens elements with the ability to vary its Focal length (and thus Angle of view) as opposed to a fixed focal In Optics, a simple lens or singlet lens is a lens consisting of a single simple element A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these out and produce a design that is suitable for photographic use and possibly mass production.

There is no major 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. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are

A lens may be permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths, apertures, and other properties. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light.

Construction

The zoom lens assembly of the Canon Elph

A practical camera lens will most often incorporate an aperture adjustment mechanism, usually an iris diaphragm, to regulate the amount of light that may pass. A zoom lens is a mechanical assembly of lens elements with the ability to vary its Focal length (and thus Angle of view) as opposed to a fixed focal In Optics, a diaphragm is a thin opaque structure with an opening ( Aperture) at its centre In early camera models a rotating plate or slider with different sized holes was used. These Waterhouse stops may still be found on relatively modern, specialized lenses. The Waterhouse stop or Waterhouse diaphragm is an interchangeable diaphragm with an Aperture (hole for controlling the entry of light into a A shutter, to regulate the time during which light may pass, may be incorporated within the lens assembly (for better quality imagery), or may be within the camera, or even, rarely, in front of the lens. In Photography, a shutter is a device that allows light to pass for a determined period of time for the purpose of exposing Photographic film or a light-sensitive Some cameras with leaf shutters in the lens omit the aperture, using the shutter to perform this function.

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. In Geometrical optics, a focus, also called an image point, is the point where Light rays originating from a point on the object converge. Some lenses include a cam system which may vary the distance between the groups to provide better performance when the lens is focused at different distances. This system is usually referred to differently by different manufacturers for marketing purposes. Nikon calls this technology CRC (close range correction) while Hasselblad uses the term FLE (floating lens element)[1]. ( also known as Nikon or Nikon Corp, is a Multinational corporation headquartered in Tokyo Japan specializing in Optics Victor Hasselblad AB is a Swedish manufacturer of Medium-format Cameras and photographic equipment based in Gothenburg, Sweden

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. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Sometimes lenses are made of materials such as quartz or fluorite. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Fluorite (also called fluorspar) is a Mineral composed of Calcium fluoride, Ca[[Fluorine F2]] ^[1][2][3] Various plastics, such as acrylic (the material of Plexiglass) can also be used. Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Poly(methyl methacrylate ( PMMA) or poly(methyl 2-methylpropenoate is a Thermoplastic and transparent Plastic. Occasionally, even germanium and meteoritic glass have been used. Germanium (dʒɚˈmeɪniəm is a Chemical element with the symbol Ge and Atomic number 32 ^[4] 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. 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. 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". However many modern, high performance (and high priced) lenses from popular manufacturers include molded or hybrid aspherical elements, so it 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 in a standardized manner. 1951 USAF Resolution Test Chart is a resolution test pattern conforms to MIL-STD-150A standard set by US Air Force in 1951 The quality of the lens material, of the coatings and of the internal manufacture all influence the "resolution" of the lens, even at the same F-number and focal length. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. Lens resolution is limited by diffraction, and very few photographic lenses approach this resolution. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle Ones that approach this resolution with the aperture wide open are termed diffraction limited and are usually extremely expensive. [2] Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. An optical coating is a thin layer of material deposited on an optical component such as a lens or Mirror, which alters the way in which the optic Lens flare is the light scattered in lens systems through generally unwanted image formation mechanisms such as internal reflection and Scattering from Some lenses have a UV coating to keep out the ultraviolet light that could expose photosensitive materials and result in inaccurate colors. The term "UV coating" has various meanings Ultra-violet coating of paper Ultra-violet cured coatings can be applied over ink printed on paper and dried by exposure Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Most modern optical cements which are used for bonding two glass elements together block UV light quite efficiently, which negates the need to use UV filters with most lenses. UV photographers will go to great lengths to find lenses that they can use effectively for their work, converting lenses with no cemented elements for possible UV work by polishing away the lens coatings, if present.

Aperture and focal length

One of Canon's most popular wide-angle zoom lenses, the 17–40mm f/4 L. A zoom lens is a mechanical assembly of lens elements with the ability to vary its Focal length (and thus Angle of view) as opposed to a fixed focal The EF 17-40mm 4L USM lens is a wide-angle lens made by Canon Inc

The Canon 85mm f/1. 8 is a compact lens popular with portrait photographers. Its large aperture can be used to minimize flash requirements or to produce a shallow depth of field.

The two main optical parameters of a photographic lens are the maximum aperture and the focal length. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. The focal length determines the angle of view, and the size of the image relative to that of the object, while the maximum aperture limits the brightness of the image and the fastest shutter speed usable. In Photography, angle of view describes the angular extent of a given scene that is imaged by a Camera. A popular third consideration is close focusing distance.

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 effective aperture (or entrance pupil) diameter in the same units. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. In an optical system the entrance pupil is a virtual aperture that defines the area at the entrance of the system that can accept light The lower the number, the more light per unit area is delivered to the focal plane. Larger apertures (smaller f-numbers) provide a much shallower depth of field than smaller apertures, other conditions being equal. In Optics, particularly as it relates to Film and Photography, the depth of field (DOF is the portion of a scene that appears sharp in the image Practical lens assemblies may also contain mechanisms to deal with measuring light, secondary apertures for flare reduction, [3]and mechanisms to hold 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. The single-lens reflex (SLR Camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging

Focal lengths are usually specified in millimetres (mm), but older lenses marked in centimetres (cm) and inches are still to be found. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth Inches redirects here To see the Les Savy Fav album see Inches. For a given film or sensor size, specified by the length of the diagonal, a lens may be classified as

• Normal lens: angle of view of the diagonal about 50° and a focal length approximately equal to the diagonal produces this angle. In Photography and Cinematography a normal lens is a lens that generates images that generally look "natural" to a human observer under normal
• Macro lens: angle of view narrower than 25° and focal length longer than normal. Macro photography is close-up Photography; the classical definition is that the Image projected on the "film plane" (i These lenses are used for close-ups, e. In Film, Television, and Still photography a close-up tightly frames a person or an object g. , for images of the same size as the object. They usually feature a flat field as well, which means that the subject plane is exactly parallel with the film plane.
• Wide-angle lens: angle of view wider than 60° and focal length shorter than normal.
• Telephoto lens or long-focus lens: angle of view narrower and focal length longer than normal. A distinction is sometimes made between a long-focus lens and a true telephoto lens: the telephoto lens uses a telephoto group to be physically shorter than its focal length.

The 35mm film format is so prevalent that a 90mm lens, for example, is sometimes assumed to be a moderate telephoto; but for the 7×5cm format it is normal, while on the large 5×4 inch format it is a wide-angle. In general, the smaller the film or sensor surface, the smaller the angle of view. This can be corrected with lenses with shorter focal lengths.

An example of how lens choice affects angle of view. The photos below were taken by a 35 mm camera at a constant distance from the subject.

28 mm lens	50 mm lens
70 mm lens	210 mm lens

A side effect of using lenses of different focal lengths is the different distances from which a subject can be framed, resulting in a different perspective. Perspective, in context of vision and Visual perception, is the way in which objects appear to the Eye based on their spatial attributes or 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 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.

Number of elements

The complexity of a lens—the number of elements and their degree of asphericity—depends upon the angle of view and the maximum aperture, among other variables including intended price point. 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. In photography a bellows is the pleated expandable part of a camera usually a large or medium format Camera, to allow the lens to be moved with respect

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"). Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly 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. 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 Colorimetry and Color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity 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)[4]. An optical coating is a thin layer of material deposited on an optical component such as a lens or Mirror, which alters the way in which the optic

Zoom lenses

Main article: Zoom lens

Some lenses, called zoom lenses, have a focal length that varies as internal elements are moved, typically by rotating the barrel or pressing a button which activates an electric motor. A zoom lens is a mechanical assembly of lens elements with the ability to vary its Focal length (and thus Angle of view) as opposed to a fixed focal An electric motor uses Electrical energy to produce Mechanical energy. 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.

Lens mounts

Main article: Lens mount

Many Single-lens reflex cameras, and some rangefinder cameras have detachable lenses. A lens mount is an interface — mechanical and often also electrical — between a photographic Camera body and a lens The single-lens reflex (SLR Camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging A rangefinder camera is a camera fitted with a Rangefinder: a range-finding focusing mechanism allowing the photographer to measure the subject distance and take photographs A few other types do as well, notably the Mamiya TLR cameras. A twin-lens reflex camera ( TLR) is a type of Camera with two objective lenses of the same Focal length. The lenses attach to the camera using a lens mount, which often also contains mechanical or electrical linkages between the lens and camera body. The lens mount is an important issue for compatibility between cameras and lenses; each major camera manufacturer typically has their own lens mount which is incompatible with others; notable exceptions are the Leica M39 lens mount for rangefinders, M42 lens mount for early SLRS, the later Pentax k mount, and the Four Thirds System mount for dSLRs, all of which are used by multiple camera brands. Leica Camera AG is a leading German optical company that has been designing and developing Cameras since 1913 and manufacturing them in series production since The M39 Lens mount is a Screw thread mounting system for attaching lenses to 35 mm cameras, primarily Rangefinder Leicas It The M42 Lens mount is a Screw thread mounting standard for attaching lenses to 35 mm Cameras, primarily single-lens reflex models The Pentax K mount, sometimes referred to as the "PK mount" is a Lens mount standard for mounting interchangeable Photographic lenses to 35 mm Most large-format cameras take interchangeable lenses as well, which are usually mounted in a lensboard or on the front standard.

Special-purpose photographic lenses

The world's first perspective correction lens for 35mm cameras, Nikon's 35mm f/3. 5 PC-Nikkor

• Apochromat (APO) lenses have added correction for chromatic aberration. In Optics, chromatic aberration is caused by a lens having a different Refractive index for different Wavelengths of Light
• Process lenses have extreme correction for aberrations of geometry (pincushion distortion, barrel distortion) and are generally intended for use at a specific distance.

Process and apochromat lenses are normally of small aperture, and are used for extremely accurate photographs of static objects. Generally their performance is optimized for subjects a few inches from the front of the lens, and suffers outside this narrow range.

• Enlarger lenses are made to be used with photographic enlargers (specialised projectors), rather than cameras. An enlarger is a specialised transparency Projector used to produce photographic prints from film or glass negatives using the Gelatin-silver
• Lenses for aerial photography. Aerial photography is the taking of Photographs of the ground from an elevated position
• Fisheye lenses: extreme wide-angle lenses with an angle of view of up to 180 degrees or more, with very noticeable (and intended) distortion. In Photography, a fisheye lens is a Wide-angle lens that takes in an extremely wide hemispherical image
• Stereoscopic lenses, to produce pairs of photographs which give a 3-dimensional effect when viewed with an appropriate viewer.
• Soft-focus lenses which give a soft, but not out-of-focus, image and have an imperfection-removing effect popular among portrait and fashion photographers. This article is about the album by the Norwegian band Euroboys, for the term used in Photography and Optics, see Soft focus.
• Infrared lenses .
• Ultraviolet lenses.
• Swivel lenses rotate while attached to a camera body to give unique perspectives and camera angles. Swivel lens are lens that freely rotate while attached to a camera body
• Perspective correction lenses, used in architectural photography to mitigate the effects of perspective. Perspective, in context of vision and Visual perception, is the way in which objects appear to the Eye based on their spatial attributes or These lenses are very popular with landscape and macro photographers as well. These lenses have a larger image circle than standard lenses for the format, and shifting the lens will provide the same effect as moving the entire camera in the direction of the shift. Only a few perspective control lenses for 35mm and medium format include the tilt function, usually reserved for large format cameras. These are called tilt shift lenses.

Notable photographic optical lens designs

A simple lens cleaning kit, consisting of a detergent, microfiber cloth, and an anti-dust airbrush. Microfiber ( British spelling: Microfibre) refers to synthetic fibers ( Fiber) that measure less than one denier. Dust is a general name for minute Solid particles with Diameters less than 500 micrometers. An airbrush is a small air-operated tool that sprays various media including Ink and Dye, but most often Paint by a process of Nebulization

Some notable photographic optical lens designs are:

• Angenieux retrofocus
• Cooke triplet
• Double-Gauss
• Goerz Dagor
• Leitz Elmar
• Nikon Nikkor
• Rapid Rectilinear
• Zeiss Tessar
• Zeiss Sonnar
• Zeiss Planar

Some lens manufacturers (2006):

• Canon
• Cosina
• Danubia
• Leica
• Minolta
• Nikon
• Olympus
• Pentax
• Schneider Kreuznach
• Sigma Corporation
• Tamron
• Tokina
• Zeiss

References

See also

• Anti-fogging treatment of optical surfaces
• Large format lens
• Lens (optics)
• Lens hood
• Lenses for SLR and DSLR cameras
• Teleconverter

External links

• Lens article at Camerapedia.org
• Photo.net Lens Tutorial