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In
photography Photography is the art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and int ...

photography
and
cinematography Cinematography (from ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Gre ...

cinematography
, a filter is a
camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and t ...

camera
accessory consisting of an
optical filter An optical filter is a device that selectively transmits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light ...

optical filter
that can be inserted into the
optical path The path that a light ray follows as it passes through an optical medium or system is often called the optical path. The physical length of an optical device can be reduced to less than the length of the optical path by using folded optics. The ...
. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a glass or plastic disk in a metal or plastic ring frame, which can be screwed into the front of or clipped onto the
camera lens A camera lens (also known as photographic lens or photographic objective) is an optics, optical lens (optics), lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film o ...
. Filters modify the images recorded. Sometimes they are used to make only subtle changes to images; other times the image would simply not be possible without them. In
monochrome photography Monochrome photography is photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material suc ...
, coloured filters affect the relative brightness of different colours; red lipstick may be rendered as anything from almost white to almost black with different filters. Others change the
colour balance Color (American English), or colour (English in the Commonwealth of Nations, Commonwealth English), is the characteristic of color vision, visual perception described through color ''categories'', with names such as red, orange (colour), ora ...
of images, so that photographs under incandescent lighting show colours as they are perceived, rather than with a reddish tinge. There are filters that distort the image in a desired way, diffusing an otherwise sharp image, adding a starry effect, etc. Linear and circular polarising filters reduce oblique reflections from non-metallic surfaces. Many filters absorb part of the light available, necessitating longer exposure. As the filter is in the optical path, any imperfections – non-flat or non-parallel surfaces, reflections (minimised by optical coating), scratches, dirt – affect the image. There is no universal or reliably standard naming or labelling system for filters. The
Wratten number Wratten numbers are a labeling system for optical filters, usually for Filter (photography), photographic use comprising a number sometimes followed by a letter. The number denotes the color of the filter, but is arbitrary and does not encode any ...
s adopted in the early twentieth century by
Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York Rochester ( ...

Kodak
, then a dominant force in film photography, are used by several manufacturers, but the degree of correspondence between the filters and the number labels is only approximate. Most
colour correction Color correction is a process used in stage lighting Stage lighting is the craft of as it applies to the production of , , , and other arts.
filters are somewhat more accurately identified by a code of the form CC''b'', e.g. CC50Y – CC for colour correction, = 50 for the strength of the filter (50%), and ''b'' = Y for yellow. ''
Optical filter An optical filter is a device that selectively transmits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light ...

Optical filter
s'' are used in various areas of science, including in particular
astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses mathematics, phys ...
; photographic filters are roughly the same as "optical" filters, but in practice optical filters often need far more accurately controlled optical properties and precisely defined
transmission curve The transmission curve or transmission characteristic is the mathematical function In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (a ...
s than filters only made for general photography. Photographic filters sell in larger quantities, at correspondingly lower prices, than many laboratory filters. The ''
article on optical filters
article on optical filters
'' has information relevant to photographic filters, particularly special-purpose photographic filters like '' color enhancing'' filters and high-quality photographic filters, like sharp cut-off UV filters. In ''digital'' photography the majority of filters used with film cameras have been rendered redundant by digital filters applied either in-camera or during post processing. Exceptions include the ultraviolet (UV) filter typically used to protect the front surface of the lens, the neutral density (ND) filter, the polarising filter, color-enhancing filters, and the infra red (IR) filter. The neutral density filter permits effects requiring wide apertures or long exposures to be applied to brightly lit scenes, while the graduated neutral density filter is useful in situations where the scene's
dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lem ...
exceeds the capability of the sensor. Not using optical filters in front of the lens has the advantage of avoiding the reduction of image quality caused by the presence of an extra optical element in the light path and may be necessary to avoid
vignetting In photography and optics, vignetting is a reduction of an image's brightness or saturation (color theory), saturation toward the wikt:periphery, periphery compared to the image center. The word ''wikt:vignette, vignette'', from the same roo ...
when using wide-angle lenses.


Uses

Filters in photography can be classified according to their use: *
Clear and ultraviolet Clear may refer to: Arts, entertainment, and media Music Groups * Clear (Christian band), an American CCM group from Cambridge, Minnesota * Clear (hardcore band), a vegan straight edge hardcore group from Utah Albums * Clear (Bomb the Bass album ...
*
Color correction Color correction is a process used in stage lighting Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts.
* Color conversion (or light balance) * Color separation, also called
color subtraction Subtractive color or subtractive color mixing predicts the spectral power distribution of light after it passes through successive layers of partially absorbing media. This idealized model is the essential principle of how dyes and inks are used ...
*
Contrast enhancement A contrast agent (or contrast medium) is a Chemical substance, substance used to increase the Display contrast, contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultraso ...
*
Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior ...
*
Neutral density The neutral density ( \gamma^n\, ) or empirical neutral density is a density variable used in oceanography, introduced in 1997 by David R. Jackett and Trevor McDougall.Jackett, David R., Trevor J. McDougall, 1997: A Neutral Density Variable for th ...
, including the
graduated neutral density filter A graduated neutral-density filter, also known as a graduated ND filter, split neutral-density filter, or just a graduated filter, is an optical filter that has a variable light transmission. Typically half of the filter is of neutral density whi ...
and solar filter * Polarizing *
Special effects Special effects (often abbreviated as SFX, SPFX, F/X or simply FX) are illusions or visual tricks used in the theatre Theatre or theater is a collaborative form of performing art that uses live performers, usually actors or actresses, to p ...

Special effects
of various kinds, including ** Graduated color, called color grads **
Cross screen A cross is a geometrical figure consisting of two intersecting lines or bars, usually perpendicular to each other. The lines usually run vertically and horizontally. A cross of oblique lines, in the shape of the Latin letter X, is also termed ...
and star diffractors **
Diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...
and contrast reduction ** Spot **
Close-up A close-up or closeup in filmmaking Filmmaking (film production) is the process by which a is . Filmmaking involves a number of complex and discrete stages, starting with an initial story, idea, or commission. It then continues through , ...
or macro diopters, and split diopters or split focus


Clear and ultraviolet

Clear filters, also known as window glass filters or optical flats, are transparent and (ideally) perform no filtering of incoming light. The only use of a clear filter is to protect the front of a lens. Clear glass will absorb some UV. UV filters are used to block invisible
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
light, to which most photographic sensors and film are at least slightly sensitive. The UV is typically recorded as if it were blue light, so this non-human UV sensitivity can result in an unwanted exaggeration of the bluish tint of atmospheric haze or, even more unnaturally, of subjects in open shade lit by the ultraviolet-rich sky. Normally, the glass or plastic of a camera lens is practically opaque to short-wavelength UV, but transparent to long-wavelength (near-visible) UV. A
UV filter UV filters are compounds, mixtures, or materials that block or absorb ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fu ...
passes all or nearly all of the
visible spectrum The visible spectrum is the portion of the electromagnetic spectrum The electromagnetic spectrum is the range of frequency, frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energy, photon en ...
but blocks virtually all ultraviolet radiation. (Most spectral manipulation filters are named for the radiation they pass; green and infrared filters ''pass'' their named colors, but a UV filter ''blocks'' UV.) It can be left on the lens for nearly all shots: UV filters are often used mainly for lens protection in the same way as clear filters. A strong UV filter, such as a Haze-2A or UV17, cuts off some visible light in the violet part of the spectrum, and has a pale yellow color; these strong filters are more effective at cutting haze, reduce
purple fringing In photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. ...

purple fringing
in
digital camera A digital camera is a camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behav ...

digital camera
s, and can subtly darken pale blue skies – which improves contrast between sky and clouds. Strong UV filters are also sometimes used for warming color photos taken in shade with daylight-type film. They were originally developed to increase contrast in airborne surveillance photography, and were adopted by
mountaineering Mountaineering, or alpinism, is the set of outdoor activities Outdoor recreation or outdoor activity refers to recreation Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is a ...

mountaineering
photographers to remedy the strong UV at high altitude. While in certain cases, such as harsh environments, a protection filter may be necessary, there are also downsides to this practice. Arguments for the use of protection filters include: * If the lens is dropped, the filter may well suffer scratches or breakage instead of the front lens element. * The filter can be cleaned frequently without damage to the lens surface or coatings; a filter scratched by cleaning is much less expensive to replace than a lens. * If there is blowing sand the filter will protect the front of the lens from abrasion and nicks. * A few lenses, such as some of Canon's L series lenses, require the use of a filter to complete their weather sealing. Arguments against their use include: * Adding another element may degrade image quality if its surfaces are less than perfectly flat and parallel. Filters from reputable makers are very unlikely to cause any problems, but some "bargain" products are optically inferior. * The two additional reflections at air-glass interfaces inevitably result in some light loss – at least four percent at each interface, if the surfaces are uncoated; they also increase the potential for
lens flare Lens flare refers to a phenomenon wherein light is scattered or flared in a lens system, often in response to a bright light, producing a sometimes undesirable artifact within the image. This happens through light scattered by the imaging mec ...

lens flare
problems. * Low-quality filters may cause problems with autofocus. * A filter may be incompatible with the use of a
lens hood In photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. I ...

lens hood
, since not all filters have the required threading for a screw-in hood or will allow a clip-on hood to be attached. Adding a lens hood on top of one or more filters may space the hood away from the lens enough to cause some
vignetting In photography and optics, vignetting is a reduction of an image's brightness or saturation (color theory), saturation toward the wikt:periphery, periphery compared to the image center. The word ''wikt:vignette, vignette'', from the same roo ...
. There is a wide variation in the spectral UV blocking by filters described as ultraviolet.


Color conversion

Appropriate color conversion filters are used to compensate for the effects of lighting not balanced for the film stock's rated
color temperature The color temperature of a light source is the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metal ...

color temperature
(usually 3200 K for professional
tungsten Tungsten, or wolfram, is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, ch ...

tungsten
s and 5500 K for daylight): e.g., the 80A blue filter used with film for daylight use corrects the perceived orange/reddish cast of incandescent photographic photoflood lighting (for which the usual photographic term is "
tungsten lighting An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light An electric light is a device that produces visible light Light or visible light is electromagnetic radiation within the portion of the ...
"), and significantly improves the stronger cast produced by lower-temperature household
incandescent lighting image of the tungsten Tungsten, or wolfram, is a chemical element with the Symbol (chemistry), symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identi ...
, while the 85B will correct the bluish cast of daylight photographs on tungsten film. Color correction filters are identified by non-standardised numbers which vary from manufacturer to manufacturer. The need for these filters has been greatly reduced by the widespread adoption of digital photography, since color balance may be corrected with camera settings as the image is captured, or by software manipulation afterwards. Color conversion filters (LB filters) must be distinguished from color correction filters (CC filters), which filter out a particular color cast f.e. caused by Schwarzschild effect etc.


Color subtraction

Color subtraction filters work by absorbing certain colors of light, letting the remaining colors through. They can be used to demonstrate the primary colors that make up an image. They are perhaps most frequently used in the
printing Printing is a process for mass reproducing text and images An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cru ...

printing
industry for
color separation Color printing or colour printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome A monochromic image is composed of one color (or values In ethics Ethics or moral philosophy is ...
s, and again, use has diminished as digital solutions have become more advanced and abundant. Didymium filters, sold as "color enhancement" or "fall color" filters act similarly: They remove a narrow (or broad) band of color in the yellow part of the spectrum ( 589 nm). Some
astronomical filter filters for protecting a camera from ultraviolet radiation An astronomical filter is a telescope A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to ...
s similarly use
didymium Didymium ( el, δίδυμο, twin element) is a mixture In chemistry, a mixture is a material made up of two or more different chemical substances which are not chemically combined. A mixture is the physical combination of two or more substanc ...
in heavier concentration. Even
astronomical filter filters for protecting a camera from ultraviolet radiation An astronomical filter is a telescope A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to ...
s which don't use didymium typically are some kind of narrow pass-band color filter.


Contrast enhancement

Colored filters are commonly used in
black and white Black-and-white (B/W or B&W) images combine black and white in a continuous spectrum In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is ...

black and white
photography to alter the effect of different colors in the scene, changing
contrast Contrast may refer to: Science * Contrast (vision), the difference in color and light between parts of an image * Contrast (statistics), a combination of averages whose coefficients add up to zero, or the difference between two means * Behavioral ...
recorded in black and white of the different colours. For example, a yellow filter or, more dramatically, an orange or red filter, will enhance the contrast between clouds and sky by darkening the blue sky while leaving the clouds bright (after exposure compensation). A deep green filter will also darken the sky, and additionally lighten green foliage, making it stand out against the sky. Light yellowish-green filters were used as standard portrait filters for
panchromatic film Panchromatic emulsion is a type of black-and-white Black-and-white (B/W or B&W) images combine black and white in a continuous spectrum In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), kno ...
, since they render skin-tones as light to dark grey, while darkening deep reds and blues to nearly black. A sky-blue filter (
cyan Cyan () is the color between green Green is the between and on the . It is evoked by light which has a of roughly 495570 . In systems, used in painting and color printing, it is created by a combination of yellow and ; in the , u ...

cyan
) mimics the effect of older
orthochromatic film In chemistry, orthochromasia is the property of a staining, dye or stain to not change color on binding to a target, as opposed to Metachromasia, metachromatic stains, which change color. The word is derived from the Greek ''wikt:ortho-, orthos'' ( ...
– or with a
"true blue"
filter, even older film only sensitive to blue light – rendering blue as light and red and green as dark, showing blue skies the same as overcast, with no contrast between sky and clouds, darkening blond hair, making blue eyes nearly white, and red lips nearly black. Diffusion filters have the opposite, contrast-reducing effect; in addition they "soften" focus, making small blemishes invisible.


Polarizer

A
polarizing filter A polarizer or polariser is an optical filter An optical filter is a device that selectively transmits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perc ...
, used for both
color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Engli ...
and
black-and-white photography Monochrome photography is photography Photography is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, emotional power, or conceptual ideas. T ...
, is colourless and does not affect colour balance, but filters out light with a particular direction of polarisation. This reduces oblique reflections from non-metallic surfaces, can darken the sky in colour photography (in monochrome photography colour filters are more effective), and can saturate the image more by eliminating unwanted reflections. Linear polarising filters, while effective, can interfere with metering and auto-focus mechanisms when mirrors or beam-splitters are in the light path, as in the
digital single lens reflex camera A digital single-lens reflex camera (digital SLR or DSLR) is a digital camera A digital camera is a camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elem ...
; a circular polarizer is also effective, and does not affect metering or auto-focus.


Neutral density

A
neutral density filter Set of ND filters. In photography and optics, a neutral-density filter, or ND filter, is a photographic filter, filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendit ...
(ND filter) is a filter of uniform density which attenuates light of all colors equally. It is used to allow a longer exposure (to create blur) or larger aperture (for selective focus) than otherwise required for correct exposure in the prevailing light conditions, without changing the tonal balance of the photograph. A
graduated neutral density filter A graduated neutral-density filter, also known as a graduated ND filter, split neutral-density filter, or just a graduated filter, is an optical filter that has a variable light transmission. Typically half of the filter is of neutral density whi ...
is a neutral density filter with different attenuation at different points, typically clear in one half shading into a higher density in the other. It can be used, for example, to photograph a scene with part in deep shadow and part brightly lit, where otherwise either the shadows would have no detail or the highlights would be burnt out.


Cross

A cross screen filter, also known as a star filter, creates a star pattern, in which lines radiate outward from bright objects. The star pattern is generated by a very fine
diffraction Diffraction refers to various phenomena that occur when a wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which r ...

diffraction
grating embedded in the filter, or sometimes by the use of
prisms An optical prism is a transparent optics, optical element with flat, polished surfaces that refraction, refract light. At least one surface must be angled—elements with two parallel surfaces are not prisms. The traditional geometrical shape o ...
in the filter. The number of stars varies by the construction of the filter, as does the number of points each star has.


Diffusion

A
diffusion filter In optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually ...
(also called a softening filter) softens subjects and generates a dreamy haze (''see
photon diffusion Photon diffusion is a situation where photons travel through a material without being absorbed, but rather undergoing repeated scattering events which change the direction of their path. The path of any given photon is then effectively a random walk ...
''). This is most often used for portraits. It also has the effect of reducing contrast, and the filters are designed, labeled, sold, and used for that purpose too. There are many ways of accomplishing this effect, and thus filters from different manufacturers vary significantly. The two primary approaches are to use some form of grid or netting in the filter, or to use something which is transparent but not optically sharp. Both effects can be achieved in software, which can in principle provide a very precise degree of control of the level of effect, however the "look" may be noticeably different. If there is too much contrast in a scene, the
dynamic range Dynamic range (abbreviated DR, DNR, or DYR) is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lem ...
of the digital
image sensor An image sensor or imager is a sensor A sensor is a device that produces an output signal for the purpose of sensing of a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects e ...
or film may be exceeded, which post-processing cannot compensate for, so contrast reduction at the time of image capture may be called for.


Close-up and split diopter lenses

A close-up lens is not technically a filter but accessory lens which attaches to a lens like a filter, hence the alternative but misleading term "close-up filter". They are often sold by filter manufacturers as part of their product lines, using the same holders and attachment systems. A close-up lens is a single or two-element converging
lens A lens is a transmissive optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, s ...

lens
used for close-up and
macro photography Macro photography (or photomacrography or macrography, and sometimes macrophotography) is extreme close-up photography, usually of very small subjects and living organisms like insects, in which the size of the subject in the photograph is great ...

macro photography
, and works in the same way as
spectacles Glasses, also known as eyeglasses or spectacles, are Visual perception, vision eyewear, consisting of glass or hard plastic lens (optics), lenses mounted in a frame that holds them in front of a person's Human eye, eyes, typically utilizing a b ...

spectacles
used for reading. The insertion of a converging lens in front of the taking lens reduces the
focal length The focal length of an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

focal length
of the combination.
Close-up lensImage:Lens filter set.jpg, Set of three close-up lenses In photography, a close-up lens (sometimes referred to as ''close-up filter'' or a ''macro filter'') is a simple secondary lens used to enable macro photography without requiring a specialis ...
es are usually specified by their optical power, the
reciprocal Reciprocal may refer to: In mathematics * Multiplicative inverse, in mathematics, the number 1/''x'', which multiplied by ''x'' gives the product 1, also known as a ''reciprocal'' * Reciprocal polynomial, a polynomial obtained from another poly ...

reciprocal
of the focal length in meters. Several close-up lenses may be used in combination; the optical power of the combination is the sum of the optical powers of the component lenses; a set of lenses of +1, +2, and +4 diopters can be combined to provide a range from +1 to +7 in steps of one. A split diopter has just a semicircular half of a close-up lens in a normal filter holder. It can be used to photograph a close object and a much more distant background, with everything in sharp focus; with any non-split lens the
depth of field For many cameras, depth of field (DOF) is the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image. The depth of field can be calculated based on focal length The focal length of an optical ...

depth of field
would be far too shallow.


Materials and construction

Photo filters are commonly made from
glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by ...

glass
,
resin In polymer chemistry Polymer chemistry is a sub-discipline of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, stru ...

resin
plastics similar to those used for eyeglasses (such as CR-39),
polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
and
polycarbonate Polycarbonates (PC) are a group of thermoplastic A thermoplastic, or thermosoft plastic, is a plastic polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material c ...

polycarbonate
; sometimes
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetal image:Simple Periodic Table Chart-en.svg, upright=1.75, Nonmetals (and metalloids) in the periodic table: Metalloids are i ...

acetate
is used. Historically, filters were often made from
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
, and
color gel A color gel or color filter (British spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the ...
s. While some filters are still described as gelatin or gel filters, they are no longer actually made from gelatin but from one of the plastics mentioned above. Sometimes the filter is dyed in the mass, in other cases the filter is a thin sheet of material sandwiched between two pieces of clear glass or plastic. Certain kinds of filters use other materials inside a glass sandwich; for example,
polarizers A polarizer or polariser is an optical filter An optical filter is a device that selectively transmits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perce ...
often use various special films, netting filters have
nylon Nylon is a generic designation for a family of synthetic polymerSynthetic polymers are human-made polymers, often derived from petroleum oil. From the utility point of view they can be classified into three main categories: thermoplastics, ela ...

nylon
netting, and so forth. The rings on screw-on filters are often made of aluminum, though in more expensive filters
brass Brass is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appea ...

brass
is used. Aluminum filter rings are much lighter in weight, but can "bind" to the aluminum lens threads they are screwed in to, requiring the use of a filter wrench to get the filter off of the lens. Aluminum also dents or deforms more easily. High quality filters are multi-coated, with multiple-layer
optical coating An optical coating is one or more thin layers of material deposited on an optical component such as a lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a ...
s to reduce reflections. Uncoated filters can reflect up to 12% of the light, single-coated filter can reduce this considerably, and multi-coated filters can allow up to 99.8% of the light to pass through (0.2% unwanted reflection); the loss of light is not important, but part of the light is reflected inside the camera, producing
flare A flare, also sometimes called a fusée or bengala in some latin-speaking countries, is a type of pyrotechnic s used in the entertainment industry Pyrotechnics is the science and craft of creating such things as fireworks Fireworks ar ...

flare
and reducing the contrast of the image.


Filter sizes and mountings

Manufacturers of lenses and filters have standardized on several different sets of sizes over the years.


Threaded round filters

The most common standard filter sizes for circular filters include 30.5 mm, 35.5 mm, 37 mm, 39 mm, 40.5 mm, 43 mm, 46 mm, 49 mm, 52 mm, 55 mm, 58 mm, 62 mm, 67 mm, 72 mm, 77 mm, 82 mm, 86 mm, 95 mm, 105 mm, 112 mm 122 mm, 127 mm. The filter diameter has a steady increase from 43 to 58 mm every 3 mm and from 62 to 82 mm every 5 mm. Other filter sizes within this range may be hard to find since the filter size may be non-standard or may be rarely used on camera lenses. The specified diameter of the filter in millimeters indicates the diameter of the male threads on the filter housing. The
thread pitch A screw thread, often shortened to thread, is a helix, helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder (geometry), cylinder or cone (geometry), cone in the form ...
is 0.5 mm, 0.75 mm or 1.0 mm, depending on the ring size. A few sizes (e.g. 30.5 mm) come in more than one pitch. The filter diameter for a particular lens is commonly identified on the lens face by the

⌀
symbol. For example, a lens marking may indicate: “⌀55 mm” or “55⌀” meaning it would accept a 55 mm filter or
lens hood In photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. I ...

lens hood
. * Table notes: Most often refers to 0.75 mm pitch thread, but an (incompatible) 1.0 mm pitch thread is sometimes used instead by some manufacturers.


Square filters

For square filters, 2" × 2", 3" × 3" and 4" × 4" were historically very common and are still made by some manufacturers. 100 mm × 100 mm is very close to 4" × 4", allowing use of many of the same holders, and is one of the more popular sizes currently (2006) in use; it is virtually a standard in the
motion picture A film, also called a movie, motion picture or moving picture, is a work of visual art The visual arts are art forms such as painting Painting is the practice of applying paint Paint is any pigmented liquid, liquefiable, o ...
industry. 75 mm x 75 mm is very close to 3" × 3" and while less common today, was much in vogue in the 1990s. The French manufacturer
Cokin Cokin is a French manufacturer of optical filters for photography. The system allows filters such as rectangular graduated neutral density filters which are versatile in use. History Cokin are particularly noted for their "Creative Filter Syste ...
makes a wide range of filters and holders in three sizes which is collectively known as the Cokin System. "A" (amateur) size is 67 mm wide, “P” (professional) size is 84 mm wide, and “X Pro” is 130 mm wide. Many other manufacturers make filters to fit Cokin holders. Cokin also makes a filter holder for 100 mm filters, which they call the “Z” size. Most of Cokin's filters are made of optical resins such as CR-39. A few round filter elements may be attached to the square/rectangular filter holders, usually polarizers and gradient filters which both need to be rotated and are more expensive to manufacture. Cokin formerly (1980s through mid-1990s) had competition from Hoya's 'Hoyarex' system (75 mm x 75 mm filters mostly made from resin) and also a range made by Ambico, but both have withdrawn from the market. A small (84 mm) “system” range is still made (as of 2012) by Formatt Hitech. In general, square (and sometimes rectangular) filters from one system could be used in another system's holders if the size was correct, but each made a different system of filter holder which could not be used together. Lee, Tiffen, Formatt Hitech and Singh Ray also make square / rectangular filters in the 100 × 100 and Cokin “P” sizes. Gel filters are very common in square form, rarely being used in circular form. These are thin flexible sheets of
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
or plastic which must be held in rigid frames to prevent them from sagging. Gels are made not only for use as photo filters, but also in a wide range of colors for use in lighting applications, particularly for theatrical lighting. Gel holders are available from all of the square “system” makers, but are additionally provided by many camera manufacturers, by manufacturers of gel filters, and by makers of expensive professional camera accessories (particularly those manufacturers which target the movie and television camera markets. Square filter systems often have lens shades available to attach to the filter holders.


Rectangular filters

Graduated filters of a given width (67 mm, 84 mm, 100 mm, etc.) are often made oblong, rather than square, in order to allow the position of the gradation to be moved up or down in the picture. This allows, for example, the red part of a sunset filter to be placed at the horizon. These are used with the "system" holders described above.


Bayonet round filters

Certain manufacturers, most notably
Rollei Rollei () was a German manufacturer of optical instruments founded in 1920 by and in Braunschweig, Lower Saxony, and maker of the Rolleiflex and Rolleicord series of cameras. Later products included specialty and nostalgic type films for the ...
and
Hasselblad Victor Hasselblad AB is a Swedish Swedish or ' may refer to: * Anything from or related to Sweden, a country in Northern Europe * Swedish language, a North Germanic language spoken primarily in Sweden and Finland * Swedish alphabet, the offi ...

Hasselblad
, have created their own systems of
bayonet mount A bayonet mount (mainly as a method of mechanical attachment, as for fitting a lens A lens is a transmissive optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle ...

bayonet mount
for filters. Each design comes in several sizes, such as Bay I through Bay VIII for Rollei, and Bay 50 through Bay 104 for Hasselblad.


Series filters

Starting in the 1930s, filters were also made in a sizing system known as a series mount. The filters themselves were round pieces of glass (or occasionally other materials) with no threads. Very early filters had no rims around the glass, but the more common later production filters had the glass mounted in metal rims. To mount the filters on a camera, the filter was placed between two rings; the mount ring either screwed into the lens threads or was slipped over the lens barrel and the retaining ring screws into the mounting ring to hold the filter in place. The series designations are generally written as
Roman numerals Roman numerals are a that originated in and remained the usual way of writing numbers throughout Europe well into the . Numbers in this system are represented by combinations of letters from the . Modern style uses seven symbols, each with a ...
, I to IX, though there are a few sizes not written that way, such as Series 4.5 and Series 5.5. Most Series filter sizes are now obsolete, production having ceased by the late 1970s. However, Series 9 became a standard of the motion picture industry and Series 9 filters are still produced and sold today, particularly for professional motion picture cinematography.filmtools.com, online catalog retrieved 2011-08-13


See also

*
Color gel A color gel or color filter (British spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the ...
*
List of photographic equipment makers This list of photographic equipment makers lists companies that manufacture (or license manufacture from other companies) equipment for photography Photography is the art, application, and practice of creating durable images by recording light ...
*
Optical filter An optical filter is a device that selectively transmits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light ...

Optical filter


Footnotes


References


External links


Photography Filters


* ttp://www.lenstip.com/115.4-article-Polarizing_filters_test_Results_and_summary.html Polarizing filters test - Results and summary - Lenstip.com
Analysis of Camera Filters , Camera Filters.biz
{{Photography Optical filters
Filter Filter, filtering or filters may refer to: Science and technology Device * Filter (chemistry), a device which separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass ** Filter (aquarium), critical ...