Thread: F stops
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Old 18th October 2017
RobEW RobEW is offline
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Re: F stops

Yes, if you want to let in twice as much light, the three common ways are:

Expose for twice as long a duration
Stop down by one stop (e.g. from f4 to f2.8, or f2.8 to f2, or f2 to f1.4 etc)
Double the ISO speed (e.g from 100 to 200, or 200 to 400, or 400 to 800 etc)

Comparing lenses with different focal lenghts is a rather different matter ...
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