A pinhole doesn't have a focal length in the sense that regular lenses
do. The tiny variations in hole to film distance you are talking abour
just don't matter. The size of the hole and the distance from the film
do determine the 'speed'. The further away they are, the further out the
same amount of light is spread, but a distance difference of 10-20%
doesn't change much. The size of the hole also determines sharpness. DOF
is essentially infinite, but the sharpness over that DOF is determined
by the hole size. So we have one of those wonder tradeoffs, a reasonably
sharp pinhole is really slow.
Moose
Jim Brokaw wrote:
I bet the body-cap with pinhole is closer to 50mm... the OM back-focus is
~46mm (guessing from memory here, somebody will know for sure) although the
pinhole likely isn't exactly even with the flange front... so its probably
closer to 50mm. I got one of those pinhole body caps somewhere, I'll have to
dig it out and play with it. I suppose that could have been a TOPE subject
as well, I just now thought of that.
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