While I agree with Larry (separate post) that all of this math can be "over
done" in the case of something as "hit and miss" as pinhole: Let me
rearrange Wayne equation above to fit the current thread:
D = 0.047*sqrt(f)
is the same as
SQRT(Focal lenght)
D= -------------------- [mm]
21.3
So to summarize, the orriginal poster (George) was using 44 in the bottom
of the fraction (sorry, forgot the correct term), I was taught to use 28.4,
Renner (of Pinhole Resource) seems to use 27.1 and Waynes equation would
have us use 21.3. Not a lot of differance between mine and Wayne's (in a
75mm focal length: 0.3mm versus 0.4mm). But notice that they are both much
bigger than the original posters equation (0.2mm).
I suspect that for me (and my eyes / artistic wishes) that Wayne's equation
may be best. I found that I was often using a larger pinhole than
"optinal" to get the look I was after. But again (and I'm not the only one
that has said this): the quality of your "hole" is as (if not more)
important than it's exact size. I recently purchase one of Calumets
"Leonardo" pinhole cameras with the lazer driller pinhole (I think Pinhole
Resource actually makes these). Much sharper than anything I ever made
myself.
tomf2468@pipeline.com (Tom Ferguson)