The Primary Effects of the Exposure Triangle

The primary purpose of each of the legs in the Exposure Triangle is to obtain a properly-exposed image.  Each of the legs can be adjusted to obtain a good exposure.  One has a great deal of freedom in choosing these settings: one can move up one leg if ones moves down another and still get a well-exposed image.


Each part of the Exposure Triangle can be measured in something called “stops.”  One stop changes the exposure by a factor of two, brighter or darker.  If you change the exposure by two stops, you have changed the brightness by two factors of two, that is, by a factor of 4.  If you change the exposure by three stops, you have changed the brightness by a factor of 8 (2x2x2).

The reason why we use the word “stop” is obscure, but it will be explained (if you care) in the aperture section.

Here is a cheat sheet for the use of the term “stop”.

-3 stops Eight times darker
-2 stops Four times darker
-1 stop Two times darker
0 stops Exposed properly
+1 stop Two times lighter
+2 stops Four times lighter
+3 stops Eight times lighter

Next: Shutter Speed