Re: f-stop calculations and reciprocity failure numbers

>

Hi folks,

> each F stop is the diameter of the opening compared to the
> focal length of the lens, focussed at infinity. Each f stop admits twice as
> much or half as much light per unit of time as the next F stop above or
> below it. F stops are convenient when using a lens,

I read somewhere that the f stop is actually the "apparent diameter" of the
opening of the lens when viewed by the front side divided by its focal distance
at infinity. It is not the real opening diameter.
Can anyone comment on that?
Thanks
Joao
Received on Sat Jul 21 23:06:45 2001