# Exposure value

﻿
Exposure value

In photography, exposure value (EV) denotes all combinations of
camera shutter speed and relative aperture that give the same
exposure. The concept was developed in Germany in the 1950s
(Ray 2000),in an attempt to simplify choosing among combinations of equivalent camera settings. Exposure value also is used toindicate an interval on the photographic exposure scale, with 1 EVcorresponding to a standard power-of-2 exposure step, commonly referred to asa &ldquo;stop.&rdquo; [In optics, the term &ldquo;stop&rdquo; properlyrefers to the aperture itself, while the term &ldquo;step&rdquo; refers to adivision of the exposure scale.Some authors, e.g., Davis (1999),prefer the term &ldquo;stop&rdquo; because they refer to steps (e.g., on a step tablet)that are other than powers of 2. ISO standards generally use&ldquo;step,&rdquo; while photographers normally use &ldquo;stop.&rdquo;]

Exposure value was originally indicated by the quantity symbol$E_v$; this symbol continues to be used in ISO standards, butthe acronym EV is now more common elsewhere.

Although all camera settings with the same exposure value nominally givethe same exposure, they do not necessarily give the same picture. Theexposure time (&ldquo;shutter speed&rdquo;) determines the amount of
motion blur, as illustrated bythe two images at the right, and the relative aperture determines the
depth of field.

Formal definition

Exposure value is a base-2 logarithmic scale defined by

:$mathrm \left\{EV\right\} = log_2 \left\{frac \left\{N^2\right\} \left\{t\right\} \right\}$

where

* $N$ is the relative aperture (f-number)

* $t$ is the exposure time (&ldquo;shutter speed&rdquo;)

EV 0 corresponds to an exposure time of 1
s and a relative aperture of $f$/1.0. If the EV isknown, it can be used to select combinations of exposure time andf-number, as shown in Table 1.

Each increment of 1 in exposure value corresponds to a change of one &ldquo;step&rdquo; (or, more commonly, one &ldquo;stop&rdquo;) in exposure, i.e., half as much exposure, either by halving the exposure time or halving the aperture area, or a combination of such changes. Greater exposure values are appropriate for photography in more brightly lit situations, or for higher film speeds.

EV as an indicator of camera settings

:

Notes

References

* Adams, Ansel. 1981. "The Negative." Boston: New York Graphic Society. ISBN 0-8212-1131-5

* ANSI PH2.7-1973. "American National Standard Photographic Exposure Guide". New York: American National Standards Institute. Superseded by ANSI PH2.7-1986

* ANSI PH2.7-1986. "American National Standard for Photography &mdash; Photographic Exposure Guide". New York: American National Standards Institute

* ASA PH2.5-1960. "American Standard Method for Determining Speed of photographic Negative Materials (Monochrome, Continuous Tone)". New York: United States of America Standards Institute

* Davis, Phil. 1999. " [http://books.elsevier.com/us/focalbooks/us/subindex.asp?isbn=0240803434 Beyond the Zone System] ", 4th ed. Boston: Focal Press. ISBN 0-240-80343-4

* Jones, Loyd A., and H. R. Condit. 1941. The Brightness Scale of Exterior Scenes and the Computation of Correct Photographic Exposure. "Journal of the Optical Society of America" 31:11, Nov. 1941, 651&ndash;678

* &mdash;&mdash;&mdash;. 1948. Sunlight and skylight as determinants of Photographic exposure. I. Luminous density as determined by solar altitude and atmospheric conditions. "Journal of the Optical Society of America" 38:2, Feb. 1948, 123&ndash;178

* &mdash;&mdash;&mdash;. 1949. Sunlight and skylight as determinants of Photographic exposure. II. Scene structure, directional index, photographic efficiency of daylight, safety factors, and evaluation of camera exposure. "Journal of the Optical Society of America" 39:2, Feb. 1949, 94&ndash;135

* Ray, Sidney F. 2000. Camera Exposure Determination. In " [http://books.elsevier.com/us/focalbooks/us/subindex.asp?isbn=0240515749 The Manual of Photography] ", 9th ed. Oxford: Focal Press. ISBN 0-240-51574-9

* Eastman Kodak Company. "Existing-Light Photography", 3rd ed. Rochester, NY : Silver Pixel Press, 1996. ISBN 0-87985-744-7

ee also

* APEX system
* Exposure compensation
* Exposure meter calibration
* High dynamic range imaging

* Doug Kerr's [http://doug.kerr.home.att.net/pumpkin/APEX.pdf The Additive System for Photographic Exposure] (PDF)
* Fred Parker's [http://www.fredparker.com/ultexp1.htm#Light%20Intensity%20Chart table of exposure values] for various lighting situations

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• exposure value — (EV)    a unit used in photography to describe relative exposure. EV 0 is assigned to a specific combination of exposure time and lens aperture, such as 1 second at f/1. The difference between two exposure values is equal to the number of stops… …   Dictionary of units of measurement

• Exposure Value — Hasselblad mit Normalobjektiv. Die rötlichen Zahlen am Objektiv sind einstellbare Lichtwerte. Hier ist LW 12 eingestellt und ergibt die Zeit Blenden Paarungen, die am Objektiv ablesbar sind …   Deutsch Wikipedia

• Exposure value — Экспозиционное число …   Краткий толковый словарь по полиграфии

• Exposure compensation — is a technique for adjusting the exposure indicated by a photographic exposure meter, in consideration of factors that may cause the indicated exposure to result in aless than optimal image. Factors considered may include unusual lighting… …   Wikipedia

• Exposure — can refer toIn biology: * A condition of very poor health or death resulting from lack of protection over prolonged periods under weather, extreme temperatures or dangerous substances ( see also: hypothermia, hyperthermia, radioactive… …   Wikipedia

• Exposure (photography) — Underexposure redirects here. For the 2005 film by Oday Rasheed, see Underexposure (2005 film). A long exposure showing stars rotating around the southern and northern celestial poles. Credit: European Southern Observatory …   Wikipedia

• Exposure action value — An Exposure Action Value (EAV) or Action Value (AV) is a limit set on occupational exposure to noise where beyond those values, employers must take steps to monitor the exposure levels. These levels are measured in decibels. The American… …   Wikipedia

• Exposure at default (EAD) — is a parameter used in the calculation of economic capital or regulatory capital under Basel II for a banking institution. This is an attribute of any exposure on bank s client.DefinitionIn general EAD can be seen as an estimation of the extent… …   Wikipedia

• exposure — ex·po·sure n 1: the fact or condition of being exposed; also: the possibility of loss caused by an outside source used in insurance 2: the act or an instance of exposing 3: something that exposes someone or something; esp: something (as a… …   Law dictionary

• Value-in-use — is the net present value (NPV) of a cash flow or other benefits that an asset generates for a specific owner under a specific use. In the U.S., Value in Use is generally estimated at a use which is less than highest and best use, and therefore… …   Wikipedia