Re: New Images

----- Original Message -----
From: "Tom Miller" <tomwmiller@comcast.net>
>
> > Great shot there Tom...that is what I was thinking about in
> > order to approximate the vignetting of a short focal length
> > camera, in a digital setup, would the pinhole need to be
> > closer [into the camera body] or further away from the "film" plane?

Digital or convencional, pinhole or glass lens, it really makes no
difference, the optical principles in regard to what you are asking, are the
same.

> Thank you. The general rule is to move the pinhole closer to the
> film, or, I would guess, the CCD in a digital camera. The image I
> posted would be the equivalent of about a 12 or 13mm focal length on a
> 35mm camera. Someone else will have to refine this answer, since I
> haven't taken the digital capture plunge yet. I don't know how big a
> CCD is and how far it is recessed into the camera. It may be that you
> would need to recess the pinhole into the camera to get a really short
> focal length.

Since most digital SLRs accept lenses that non digital SLRs also accept,
CCDs are recessed into a DSLR at the same distance from the lens flange as
they are recessed for a regular non-digital SLR (Canon EOS=44mm,
Nikon=46.5mm). CCDs linear dimensions are about 66% smaller than a 35mm
film frame in most DSLRs. A 12 or 13mm focal length in a non DLSR camera
would need to be about 8 or 8.6mm, respectively, in a DSLR camera, for it to
have the same angle of view. For the metric impaired, 8.6mm is just under
3/8" and that is a very short distance! Unless a DSLR or just SLR for that
matter, has mirror lock up, it is impossible to recess a pinhole into the
camera placing it less than around 41mm from the film or CCD plane (around
41 for Nikon cameras), if you do, when the mirror moves would hit the
pinhole and get damaged. If you have mirror lock up, it is conceivable to
make a body cap that places the pinhole closer than 41mm, but I think there
will be a point before you get to 8mm focal length for which the actual body
of the camera would interfere with the angle of view. The good thing about
working with DSLRs is that it is "instant gratification" so you can do all
the tests and tries you'd like in very short time as results are
instantaneous, so if you have a DLSR and it has mirror lock up, start
recessing it until mechanical vignetting shows up. Disclaimer: if you do
it, you'd do it at your own risk.

Guillermo
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Received on Thu Mar 10 06:41:05 2005