What is a Stop?

Origin of the Term

I would like to explore exposure more. In several places in earlier posts I have used the term "stop". For those new to DSLR style photography and making adjustments yourself, the term may puzzle you. If you look up the word "stop" in the dictionary you may find a reference to "photographic stop" but I had better luck looking up "detent" (which my current spell-checker says is not a word). Imagine a wheel with small notches like the one at right. On top rests a spring with a vee shaped end which fits the notches. When you turn the wheel it will try to stop each time you reach a notch. These notches are called detents and sometimes "stops" with them you know exactly how far you've turned the wheel and you can find the same spot again any time.

You can also stop in between if you want to.

Use of the Term in Photography

In photography one stop more exposure is two times the exposure and one stop less exposure is 1/2 as much exposure. The question now is why was double and half chosen as a normal difference between exposures. Double seems like a long way. Look at the three images below. The center one is what I chose as the best exposure. The one to the left is twice the exposure or one stop greater and the one to the right is 1/2 the exposure of the center one.

The difference between the exposures is a comfortable difference to work with. It is noticeable but not extreme. As with the wheel above your camera can be set in between stops if you feel that a whole stop goes too far. Most cameras adjust to 1/3 stops and not many photographers find a need for a finer adjustment than that.

There are three adjustments on your camera that affect the exposure so come back and we'll tackle them one at a time.