Re: pinhole film flatness, depth of focus, etc

the difference in f will result in a difference in exposure, (you see
this all the time with short systems with flat film planes) but the
sharpness of the image is determined mostly by the size of the pinhole.
At very small pinhole sizes diffraction effects limit the sharpness
relative to distance to the film plane, but you' ve got to have a
pretty darn small pinhole to notice those.

Nick

On Jul 26, 2004, at 7:34 AM, George L Smyth wrote:

>
> Murray -
>
> Actually, I have put filters in front of and behind pinholes and not
> seen a difference, so I would not make the second assumption. With
> the first assumption, I have seen that objects far away will be "less
> sharp" than very close objects, probably because of atmospheric
> effects. Just my observations, not something measurable.
>
> I am guessing that one will not be able to detect much as far as focus
> is concerned when dealing with film flatness. I would imagine that it
> does make a difference becuase the F stop will be different, but then
> again theoretically you have that situation with a perfectly flat
> sheet of film since the edges will be further than the center. As far
> as this being measurable or noticeable, I doubt it.
>
> Cheers -
>
> george
>
> -----
> http://www.GLSmyth.com
> http://DRiPInvesting.org
>
> --- On Sat 07/24, Uptown Gallery < murray@uptowngallery.org > wrote:
> From: Uptown Gallery [mailto: murray@uptowngallery.org]
> To: pinhole-discussion@spitbite.org
> Date: Sat, 24 Jul 2004 22:15:48 -0400
> Subject: [pinhole-discussion] pinhole film flatness, depth of focus,
> etc
>
> depth of field is said to be for, all practical purposes, infinite
> with<br>typical large f-number pinholes.<br><br>we also know that
> depth of focus (behind the aperture) is 'less critical'<br>because
> filter defects, dust etc., that show up in front of a pinhole,
> do<br>not if placed BEHIND the pinhole.<br><br>Since pinhole is
> 'afocal', is there any problem with film flatness and<br>pinhole,
> especially large and thin
> film?
> <br><br>Thanks<br><br>Murray<br><br><br><br>___________________________
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Received on Mon Jul 26 06:02:15 2004