What's a "Stop"

Apr 19, 2007
i have been wondering about the term "one stop" as in f/2.8 is 1 stop faster than f/4. Perhaps some people an enlighten (pun intended) me

- why do some people say a stop is 2.0, 2.8, 4.0, 5.6 while others would include smaller increments (2.0, 2.8 3.5, 4.0 4.5 5.6 etc)

- why is it called a 'stop'? would STEP make more sense?

- what's it really mean? So if 2.8 is 'a full stop faster' then 4.0, ok, we know we get more light (and narrower DOF) but does this translate uniformly to a shutter speed (eg 1/100 from 1/60)?? I don't think it does but i am at a loss for why we say this 'one stop faster'...

Happy Friday and hope to see some interesting responses

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