> There is no "rule of thumb", just plain physics of light.
> This case is in no way different than if you were using a glass lens.
I guess you could say the rule of thumb is to add 2 stops every time you
double the focal lenngth.
You can think of it this way... If you have a 50mm lens at f/16, divide 50
by 16 and the opening would is 3.125mm. If you had that same opening on a
100mm lens, take 100 divided by 3.125, and you get f/32. Two stops from
f/16.
John
Received on Sat Dec 1 00:46:25 2001
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