----- Original Message -----
From: "Tom Harvey" <harveyt@aracnet.com>
> It's the "very, very" that I wonder about.
> I believe that Zernike Au has said that he used the smaller aperture
> because tested out sharper.
> Aside from lengthening exposure times, would using small size
> pinholes on cameras with focal lengths of twice the "optimal"
> focal length be any less sharp?
Tom,
All optimum pinhole formulas, starting with Lord Rayleigh's (1891) to
the most modern one, like the one in M.Young's article foound at PV site, can be
expressed as:
Diameter = SQRT( K * F * Lambda )
That constant K has taken many values, some based on analitical reasons, some
based on experimental reasons. You implicitly mentioned 2 values, the one in
Renner's book, which BTW is congruent with modern formulations and Zernike's,
which you mention to have read was found experimentally and gives way smaller
diameters than the modern scientific formulation. I know of another
experimental value, that found by C.Patton, which oddly enough, gives larger
diameters. So there you have it, science says something and 2 pinholers have
found experimentally that a larger hole produces better resolution (Patton) and
the other (Zernike) than a smaller hole produces better results. I have to
mention that Patton's value doesn't deviate drastically away from the
"scientific formulation" as Zernike's does.
Since pinhole is not about "sharpness", use any pinhole size for a particular
distance pinhole-film, but I suggest you use what I call the "scientific
formulation" as the starting point from which deviate.
Guillermo
Received on Mon May 6 22:10:09 2002
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