TheInfoList

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 ...

, exposure is the amount of light per unit area (the image plane
illuminance In photometryPhotometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical ob ...

times the exposure time) reaching a frame of
photographic film Photographic film is a strip or sheet of transparent film baseA film base is a transparent substrate which acts as a support medium for the photosensitive emulsion An emulsion is a mixture of two or more liquids that are normally Miscibil ...
or the surface of an electronic
image sensor An image sensor or imager is a that detects and conveys information used to make an . It does so by converting the variable of light s (as they or objects) into , small bursts of that convey the information. The waves can be light or other ...
, as determined by
shutter speed In 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. There is no generall ...

, lens
aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of ray (optics), rays that come to a focus (optics), focus ...
, and scene
luminance Luminance is a measure of the per of travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given . is the for the ''subjective'' ...

. Exposure is measured in
lux The lux (symbol: lx) is the SI derived unit SI derived units are units of measurement ' Measurement is the number, numerical quantification (science), quantification of the variable and attribute (research), attributes of an object or event, wh ...

second The second (symbol: s, also abbreviated: sec) is the base unit of time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, th ...
s, and can be computed from
exposure value In 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. There is no generally agr ...
(EV) and scene luminance in a specified region. An "exposure" is a single shutter cycle. For example, a long exposure refers to a single, long shutter cycle to gather enough dim light, whereas a
multiple exposure 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. ...
involves a series of shutter cycles, effectively layering a series of photographs in one image. The accumulated ''photometric exposure'' (''H''v) is the same so long as the total exposure time is the same.

Definitions

Radiant exposure of a ''surface'', denoted ''H''e ("e" for "energetic", to avoid confusion with
photometricPhotometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electroma ...
quantities) and measured in , is given by :$H_\mathrm = E_\mathrmt,$ where *''E''e is the
irradiance In radiometry Radiometry is a set of techniques for measuring ' Measurement is the numerical quantification of the attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measure ...

of the surface, measured in ; *''t'' is the
exposure duration File:Truck with motion blur.jpg, Slow shutter speed combined with panning the camera can achieve a motion blur for moving objects. In photography Photography is the art Art is a diverse range of (products of) human activities invo ...
, measured in s.

Luminous exposure

Luminous exposure of a ''surface'', denoted ''H''v ("v" for "visual", to avoid confusion with
radiometric Radiometry is a set of techniques for measuring Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measurement are dependent on the ...

quantities) and measured in , is given by :$H_\mathrm = E_\mathrmt,$ where *''E''v is the
illuminance In photometryPhotometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical ob ...

of the surface, measured in lx; *''t'' is the exposure duration, measured in s. If the measurement is adjusted to account only for light that reacts with the photo-sensitive surface, that is, weighted by the appropriate
spectral sensitivity Spectral sensitivity is the relative efficiency of detection, of 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 ...
, the exposure is still measured in radiometric units (joules per square meter), rather than photometric units (weighted by the nominal sensitivity of the human eye). Only in this appropriately weighted case does the ''H'' measure the effective amount of light falling on the film, such that the characteristic curve will be correct independent of the spectrum of the light. Many photographic materials are also sensitive to "invisible" light, which can be a nuisance (see
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 (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), ...
and
IR filter Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block near-infrared Infrared (IR), sometimes called infrared light, is (EMR) with s longer than those of . It is therefore invisible ...
), or a benefit (see
infrared photography ''Top:'' tree photographed in the near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is gen ...
and
full-spectrum photography Full-spectrum photography is a subset of multispectral imaging, defined among photography enthusiasts as imaging with consumer cameras the full, broad spectrum of a film or camera sensor An image sensor or imager is a sensor that detects and ...
). The use of radiometric units is appropriate to characterize such sensitivity to invisible light. In
sensitometric Sensitometry is the scientific study of light-sensitive materials, especially photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microsco ...
data, such as characteristic curves, the ''log exposure'' is conventionally expressed as log10(''H''). Photographers more familiar with base-2 logarithmic scales (such as
exposure value In 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. There is no generally agr ...
s) can convert using .

Optimum exposure

"Correct" exposure may be defined as an exposure that achieves the effect the photographer intended. A more technical approach recognises that a photographic film (or sensor) has a physically limited useful exposure range, sometimes called its
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 lemon ...
. If, for any part of the photograph, the actual exposure is outside this range, the film cannot record it accurately. In a very simple model, for example, out-of-range values would be recorded as "black" (underexposed) or "white" (overexposed) rather than the precisely graduated shades of colour and tone required to describe "detail". Therefore, the purpose of exposure adjustment (and/or lighting adjustment) is to control the physical amount of light from the subject that is allowed to fall on the film, so that 'significant' areas of shadow and highlight detail do not exceed the film's useful exposure range. This ensures that no 'significant' information is lost during capture. The photographer may carefully overexpose or underexpose the photograph to ''eliminate'' "insignificant" or "unwanted" detail; to make, for example, a white altar cloth appear immaculately clean, or to emulate the heavy, pitiless shadows of
film noir Film noir (; ) is a cinematic term used primarily to describe stylish Hollywood Hollywood is a neighborhood A neighbourhood (British English British English (BrE) is the standard dialect of the English language Englis ...
. However, it is technically much easier to discard recorded information during post processing than to try to 're-create' unrecorded information. In a scene with strong or harsh lighting, the ''ratio'' between highlight and shadow luminance values may well be larger than the ''ratio'' between the film's maximum and minimum useful exposure values. In this case, adjusting the camera's exposure settings (which only applies changes to the whole image, not selectively to parts of the image) only allows the photographer to choose between underexposed shadows or overexposed highlights; it cannot bring both into the useful exposure range at the same time. Methods for dealing with this situation include: using what is called
fill light A typical shoulder or back-side lamp to create contrast between the background and center object so as to give a three-dimensional appearance.">Backlighting (lighting design)">shoulder or back-side lamp to create contrast between the background and ...
ing to increase the illumination in shadow areas; using 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 An optical filter is a device that selectively transmits light Light or visible light ...
, flag, scrim, or gobo to reduce the illumination falling upon areas deemed too bright; or varying the exposure between multiple, otherwise identical, photographs ( exposure bracketing) and then combining them afterwards in an HDRI process.

Overexposure and underexposure

A photograph may be described as ''overexposed'' when it has a loss of highlight detail, that is, when important bright parts of an image are "washed out" or effectively all white, known as "blown-out highlights" or " clipped whites". A photograph may be described as ''underexposed'' when it has a loss of shadow detail, that is, when important dark areas are "muddy" or indistinguishable from black, known as "blocked-up shadows" (or sometimes "crushed shadows", "crushed blacks", or "clipped blacks", especially in video). As the adjacent image shows, these terms are technical ones rather than artistic judgments; an overexposed or underexposed image may be "correct" in the sense that it provides the effect that the photographer intended. Intentionally over- or underexposing (relative to a standard or the camera's automatic exposure) is casually referred to as " exposing to the right" or "exposing to the left" respectively, as these shift the histogram of the image to the right or left.

Exposure settings

Manual exposure

In manual mode, the photographer adjusts the lens aperture and/or
shutter speed In 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. There is no generall ...

to achieve the desired exposure. Many photographers choose to control aperture and shutter independently because opening up the aperture increases exposure, but also decreases 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 ...

, and a slower shutter increases exposure but also increases the opportunity for
motion blur Motion blur is the apparent streaking of moving objects in a photograph A photograph (also known as a photo) is an image An SAR radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide vol ...
. "Manual" exposure calculations may be based on some method of
light meter A light meter is a device used to measure the amount of light. In photography Photography is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, em ...
ing with a working knowledge of
exposure value In 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. There is no generally agr ...
s, the APEX system and/or the Zone System.

Automatic exposure

A camera in automatic exposure or autoexposure (usually initialized as AE) mode automatically calculates and adjusts exposure settings to match (as closely as possible) the subject's mid-tone to the mid-tone of the photograph. For most cameras, this means using an on-board TTL
exposure meter A light meter is a device used to measure the amount of light. 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 ...
.
Aperture priority Aperture priority, often abbreviated ''A'' or ''Av'' (for aperture value) on a camera mode dial, is a setting on some cameras that allows the user to set a specific aperture value (f-number) while the camera selects a shutter speed to match it that ...
(commonly
abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full version of the word or phrase; for example, the word ''abbrevia ...
as ''A'', or ''Av'' for ''aperture value'') mode gives the photographer manual control of the aperture, whilst the camera automatically adjusts the shutter speed to achieve the exposure specified by the TTL meter.
Shutter priority Shutter priority (usually denoted as S on the mode dial), also called time value (abbreviated as Tv), refers to a setting on some cameras that allows the user to choose a specific shutter speed File:Truck with motion blur.jpg, Slow shutter ...
(often abbreviated as ''S'', or ''Tv'' for ''time value'') mode gives manual shutter control, with automatic aperture compensation. In each case, the actual exposure level is still determined by the camera's exposure meter.

Exposure compensation

The purpose of an
exposure meter A light meter is a device used to measure the amount of light. 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 ...
is to estimate the subject's mid-tone
luminance Luminance is a measure of the per of travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given . is the for the ''subjective'' ...

and indicate the camera exposure settings required to record this as a mid-tone. In order to do this it has to make a number of assumptions which, under certain circumstances, will be wrong. If the exposure setting indicated by an exposure meter is taken as the "reference" exposure, the photographer may wish to deliberately ''overexpose'' or ''underexpose'' in order to compensate for known or anticipated metering inaccuracies. Cameras with any kind of internal exposure meter usually feature an exposure compensation setting which is intended to allow the photographer to simply offset the exposure level from the internal meter's estimate of appropriate exposure. Frequently calibrated in stops, also known as EV units, a "+1" exposure compensation setting indicates one stop more (twice as much) exposure and "–1" means one stop less (half as much) exposure. Exposure compensation is particularly useful in combination with auto-exposure mode, as it allows the photographer to ''bias'' the exposure level without resorting to full manual exposure and losing the flexibility of auto exposure. On low-end video camcorders, exposure compensation may be the only manual exposure control available.

Exposure control

An appropriate exposure for a photograph is determined by the sensitivity of the medium used. For photographic film, sensitivity is referred to as
film speed Film speed is the measure of a photographic film Photographic film is a strip or sheet of transparent coated on one side with a containing microscopically small light-sensitive crystals. The sizes and other characteristics of the cryst ...
International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm Norm, the Norm or NORM may refer to: In academic discipline ...
(ISO). Faster film, that is, film with a higher ISO rating, requires less exposure to make a readable image.
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 ...

s usually have variable ISO settings that provide additional flexibility. Exposure is a combination of the length of time and the
illuminance In photometryPhotometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical ob ...

at the photosensitive material. Exposure time is controlled in 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 ...

by
shutter speed In 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. There is no generall ...

, and the illuminance depends on the lens
aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of ray (optics), rays that come to a focus (optics), focus ...

and the scene
luminance Luminance is a measure of the per of travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given . is the for the ''subjective'' ...

. Slower shutter speeds (exposing the medium for a longer period of time), greater lens apertures (admitting more light), and higher-luminance scenes produce greater exposures. An approximately correct exposure will be obtained on a sunny day using ISO 100 film, an aperture of and a shutter speed of 1/100 of a second. This is called the
sunny 16 rule In photography, the sunny 16 rule (also known as the sunny rule) is a method of estimating correct daylight exposures without a light meter A light meter is a device used to measure the amount of light. In photography Photography is the ...
: at an aperture of on a sunny day, a suitable shutter speed will be one over the film speed (or closest equivalent). A scene can be exposed in many ways, depending on the desired effect a photographer wishes to convey.

Reciprocity

An important principle of exposure is
reciprocity Reciprocity may refer to: Law and trade * Reciprocity (Canadian politics), free trade with the United States of America ** Reciprocal trade agreement, entered into in order to reduce (or eliminate) tariffs, quotas and other trade restrictions on ...
. If one exposes the film or sensor for a longer period, a reciprocally smaller aperture is required to reduce the amount of light hitting the film to obtain the same exposure. For example, the photographer may prefer to make his sunny-16 shot at an aperture of (to obtain a shallow depth of field). As is 3 stops "faster" than , with each stop meaning double the amount of light, a new shutter speed of (1/125)/(2·2·2) = 1/1000 s is needed. Once the photographer has determined the exposure, aperture stops can be traded for halvings or doublings of speed, within limits. The true characteristic of most photographic emulsions is not actually linear (see
sensitometry Sensitometry is the scientific study of light-sensitive materials, especially photographic film Photographic film is a strip or sheet of transparent coated on one side with a containing microscopically small light-sensitive crystals. The ...
), but it is close enough over the exposure range of about 1 second to 1/1000 of a second. Outside of this range, it becomes necessary to increase the exposure from the calculated value to account for this characteristic of the emulsion. This characteristic is known as ''
reciprocity failure In 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. There is no generally agreed ...
''. The film manufacturer's data sheets should be consulted to arrive at the correction required, as different emulsions have different characteristics.
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 ...

image sensor An image sensor or imager is a that detects and conveys information used to make an . It does so by converting the variable of light s (as they or objects) into , small bursts of that convey the information. The waves can be light or other ...
s can also be subject to a form of reciprocity failure.

Determining exposure

The Zone System is another method of determining exposure and development combinations to achieve a greater tonality range over conventional methods by varying the contrast of the film to fit the print contrast capability. Digital cameras can achieve similar results (
high dynamic range High dynamic range (HDR) is a 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 ...
) by combining several different exposures (varying shutter or diaphragm) made in quick succession. Today, most cameras automatically determine the correct exposure at the time of taking a photograph by using a built-in
light meter A light meter is a device used to measure the amount of light. In photography Photography is the art Art is a diverse range of (products of) human activities involving creative imagination to express technical proficiency, beauty, em ...
, or multiple point meters interpreted by a built-in computer, see
metering modeIn 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. It ...
. Negative and print film tends to bias for exposing for the shadow areas (film dislikes being starved of light), with digital favouring exposure for highlights. See latitude below.

Latitude

Latitude is the degree by which one can over, or under expose an image, and still recover an acceptable level of quality from an exposure. Typically negative film has a better ability to record a range of brightness than slide/transparency film or digital. Digital should be considered to be the reverse of print film, with a good latitude in the shadow range, and a narrow one in the highlight area; in contrast to film's large highlight latitude, and narrow shadow latitude. Slide/Transparency film has a narrow latitude in both highlight and shadow areas, requiring greater exposure accuracy. Negative film's latitude increases somewhat with high ISO material, in contrast digital tends to narrow on latitude with high ISO settings.

Highlights

Areas of a photo where information is lost due to extreme brightness are described as having "blown-out highlights" or "flared highlights". In digital images this information loss is often irreversible, though small problems can be made less noticeable using photo manipulation software. Recording to RAW format can correct this problem to some degree, as can using a digital camera with a better sensor. Film can often have areas of extreme overexposure but still record detail in those areas. This information is usually somewhat recoverable when printing or transferring to digital. A loss of highlights in a photograph is usually undesirable, but in some cases can be considered to "enhance" appeal. Examples include black-and-white photography and portraits with an out-of-focus background.

Blacks

Areas of a photo where information is lost due to extreme darkness are described as "crushed blacks". Digital capture tends to be more tolerant of underexposure, allowing better recovery of shadow detail, than same-ISO negative print film. Crushed blacks cause loss of detail, but can be used for artistic effect.

*
Bulb (photography) The Bulb setting (abbreviated B) on camera shutters is a momentary-action mode that holds shutters open for as long-exposure photography, long as a photographer depresses the shutter-release button. The Bulb setting is distinct from shutter's T ...
* Exposure bracketing *
Exposure value In 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. There is no generally agr ...
*
Film speed Film speed is the measure of a photographic film Photographic film is a strip or sheet of transparent coated on one side with a containing microscopically small light-sensitive crystals. The sizes and other characteristics of the cryst ...
* Gray card *
High-dynamic-range imaging High-dynamic-range imaging (HDRI) is a technique used in photographic imaging and films, and in ray-traced computer-generated imaging, to reproduce a greater range of luminosity Luminosity is an absolute measure of radiated electromagneti ...
*
Light painting Light painting, painting with light, light drawing, or light art performance photography are terms that describe photography, photographic techniques of moving a light source while taking a long exposure photograph, either to illuminate a subject ...

*
Light value Light or visible 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 through Spacetime, spa ...
* Long exposure multiple flash photographic technique *
Multiple exposure 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. ...
*
Night photography File:Long exposure night shot of Sutton pace.jpg, 250px, A London taxi turning outside the railway station at Sutton, London Night photography (also called nighttime photography) refers to photography, the activity of capturing photograph, ima ...

*
Sensitometry Sensitometry is the scientific study of light-sensitive materials, especially photographic film Photographic film is a strip or sheet of transparent coated on one side with a containing microscopically small light-sensitive crystals. The ...
(and Hurter–Driffield curves) *
Shutter speed 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 ...

(also called
exposure time Exposure or Exposures may refer to: People * The Exposures, a pseudonym for German electronic musician Jan Jeline Arts, entertainment, and media Films * ''Exposure'' (film), a 1932 American film * ''Exposure'', another name for the 1991 movie ...

) *
Zebra patterning Zebra patterning (or zebra stripes) is a feature found on some wikt:prosumer#Etymology_2, prosumer and most professional video cameras to aid in correct exposure. When enabled, areas of the image over a certain threshold are filled with a striped ...