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amirzur

Perhaps a bit of a silly question, but how were these standard f-stop numbers decided on? What effect does doubling an f-stop (1.4 to 2.8) have on exposure or on the overall image?

sagoyal

@amirzur so I believe the way it works is that decrease the f-stop ie going from 2 to 1.4, causes the exposure to get doubled. This is because notice that F-stop are in terms of multiples of $\sqrt{2}$ which means that according to the formula in the second line the amount of exposure doubles since the denominator ($N$) is getting smaller.

amirzur

Ah I see, that makes sense. Thank you for the explanation!