In a message dated 8/3/00 12:49:12 PM US Eastern Standard Time,
jlind@xxxxxxxxxxx writes:
<< Considering lens speeds, there is often a misconception about f/3.5 versus
f/4. They are only 1/3 stop apart, not the half stop many think it is.
That's right, f/3.5 is only 1/3 stop faster. For me, f/3.5 versus f/4
wouldn't be a consideration.
>>
I was always under the impression that the difference between aperture
settings on the lens was one stop difference in light transmission. That is,
the difference is measured by light transmission, not by numerical value. If
so, how could there be a 1/2 or 1/3 difference in light transmission? At the
same shutter speed, there should be twice as much light transmitted by the
f3.5 aperture setting than by the f4. The consistency of the one stop rule is
what makes possible the exposure correlation between aperture and shutter
speeds. For example, f3.5 at 1/125 second would allow the same light
transmission as f4 at 1/60; f8 at 1/250 second would allow the same light
transmission as f11 at 1/125. In other words, to maintain exposure
consistency, if light transmission is doubled then shutter speed is halved;
if light transmission is halved then shutter speed is doubled.
Have I just been confused for the past 50 years?
Robert
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