F-numbers less than f/1.2 - how many stops?
I never seemed to run into this problem before because I don't own/use anything this fast until now.
I know the 'traditional' f-stops and how to calculate them etc for apertures f/1.2 and larger (numerical value).
f/1.2 is 1/3 faster than f/1.4.
but how many stops faster is f/0.95 to f/1.4?
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#2. "RE: F-numbers less than f/1.2 - how many stops?" | In response to Reply # 0MotoMannequin Registered since 11th Jan 2006Mon 18-Jan-10 04:38 PM
The formula is 2*log2(A1/A2) where "log2" means logarithm base 2 and A1 & A2 are the apertures you want to compare.
You might have difficulty finding a calculator that does log2 but if you have access to Excel then you can write this as =2*log(A1/A2,2)
f/1.2 is ½ stop faster than f/1.4
f/0.95 is 1.12 stops faster than f/1.4.
To calculate the change in shutter or ISO, new shutter/ISO = (old shutter/ISO)/(2*number of stops) e.g. 1/10" shutter at f/1.4, change aperture to f/0.95 and you will get equivalent exposure at 1/22"
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