Thread: F stops
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Old 18th October 2017
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Re: F stops

Quote:
Originally Posted by RobEW View Post
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 ...
Almost, but not quite. Just to be pedantic, whilst the 1st two methods capture twice as much light, doubling the ISO speed merely increases the sensor amplification - hence also increasing the noise being captured.
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