P3D Re: optics question

[abram klooswyk <abram.klooswyk@xxxxxx>]

>Tom Deering wrote (digest 2831):
>I'd like to make a stereo macro camera, with just one big SLR-sized lens.
>I'd place a pair of fixed apertures behind this lens, separated by a
>septum. <
>Tony Alderson wrote (digest 2833):
>...but if memory serves, this was one of Pat
>Whitehouse's projects. I also have an old issue of the PSA Journal that
>discusses a similar conversion on a 120 roll film camera.

The famous Baby-Bertha's of Pat Whitehouse didn't have a single lens
scheme, she moved the optical center of two lenses closer together after
grinding (!) away part of the lenses.

Koo Ferwerda himself used the scheme Tom Deering describes, based upon a
an old Nil Melior roll film camera (Buy His Book "The World of 3-D"! ). 
The stereo base was 9, 6 or 4 mm. Behind both apertures Koo placed a
prism to guide the light to the film. This is a solution to mayor
problem of the design: you don't want film chips only 4 mm wide I
suppose. 
Only very few people have adopted this design. Don't try it if you have
no education in fine mechanics.

The original idea of using one lens with excentric apertures comes from 
Sir David Brewster, in his 1856 book on "The Stereoscope" he describes
a three inches lens with a lens cover having an aperture of a quater of
an inch (page 138). He apparantly did this only in theory, to critise
large lenses.

However, the principle works as you can find out by placing a monocamera
on a tripod a take two pictures through a lenshood with an excentric
hole in it, turn the hood 180 degrees for the second exposure.
The results however will show vignetting and are not good enough  in
practice. Vignetting indeed is a problem of the scheme. 
Why don't you buy a macro stereo lens for an SLR? 

Abram Klooswyk.


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