New To Photography:What is Exposure Value?

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This page is a chapter in the book Appendix C - Camera Metering (measuring light) and Sunny 16 rule.
Question: We read things like 'change the exposure by +2EV' or the exposure is out by -1EV. What does this term 'EV' mean?

Answer: EV stands for ‘Exposure Value’ and it has two different but related meanings:

The meaning we use today is to express a relative change in exposure.
We often interchange the term 'stops', i.e. over or under exposing by one stop.
Thus when we say +2EV we mean increasing the exposure by 2 stops,
and similarly -1EV means decreasing the exposure by 1 stop.

Your hear or read about 'bracketing the exposure by ±2EV' which means you take a photo
at the recommended or metered exposure followed by two more exposures:
one two stops over exposed and another two stops under exposed.

The second and now less common meaning for EV is when it is used as an absolute measure of light from a subject.
Before the advent of built in light meters photographers had a good idea of what EV value (and therefore what shutter speed/aperture settings),
would correspond to typical conditions or the scene they metered using a separate light meter.
For example a bright sunlit scene might be EV 15, sunset would be about EV 12 (i.e. 3 stops darker), indoor concerts EV 8 etc.
(Note: EV 15 is the basis of the Sunny 16 rule)

The following table apertures and shutter speeds is based on a fixed ISO of 100.
You can use the table to determine an appropriate manual Aperture and Shutter Speed setting for the scene:

ISO 100 f/.....
Aperture 1.4 2.0 2.8 4.0 5.6 8.0 11 16 22 32
Shutter Exposure Value
1 1 2 3 4 5 6 7 8 9 10
1/2 2 3 4 5 6 7 8 9 10 11
1/4 3 4 5 6 7 8 9 10 11 12
1/8 4 5 6 7 8 9 10 11 12 13
1/15 5 6 7 8 9 10 11 12 13 14
1/30 6 7 8 9 10 11 12 13 14 15
1/60 7 8 9 10 11 12 13 14 15 16
1/125 8 9 10 11 12 13 14 15 16 17
1/250 9 10 11 12 13 14 15 16 17 18
1/500 10 11 12 13 14 15 16 17 18 19
1/1000 11 12 13 14 15 16 17 18 19 20
1/2000 12 13 14 15 16 17 18 19 20 21
Eg: a sunset (EV 12) could be taken with any shutter speed and aperture with a number 12 at the intersection (eg. f/2.8 1/500th second or f/16 at 1/15th second).

For ISO 200 add 1 to the EV; ISO 400 add 2 to the EV and so on.
Previous: New To Photography:Exposure Compensation (Ev) Appendix C - Camera Metering (measuring light) and Sunny 16 rule Next: Appendix D - Full Frame vs APS-C/DX crop factor w/example

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