Re: Requirements for a new stereo camera

[bercov@xxxxxxxxxxx (John Bercovitz)]

Well, _this_ is embarrassing!  I worked out what I consider to be 
an ideal set of numbers for a stereo camera some years ago, and 
then again a few months ago, and when I went to post on this 
subject on Monday, I couldn't find my notes so I winged it.  Not a 
very good idea as it only adds to the confusion.  8-(  This 
morning I found what I'd come up with.  I also have a graphic file 
which I can make into a GIF and maybe Bob could put it on bobcat.  
Bobcat on the web is ftp://bobcat.etsu.edu/pub/photo/photo-3d/
I'll call the GIF idlcam.gif.  Do we need and ISU ideal camera 
directory on bobcat?  Could the French Stereo Club paper go in 
there?

Here are the basic specs:
*interchangeable fixed focal length lens sets 
*lenses 67 on center
*film gates on 71.25 mm centers (= 15 perfs)
*aperture width 33.625 mm (leaving 2 mm on film between chips)

The wide film gates allow for a whole lot of window manipulation 
if you're using any reasonable-length pair of lenses.  This is 
because with all the extra width, you can change the effective 
center distance of the film gates by masking down in the mount.

Some instances of the span of window distances which are achievable 
by shifting the 33.625 mm film chip width on the mount aperture:

F is lens focal length 
L is lens separation (on centers)
R is distance from lenses to stereo window
A is effective aperture (film gate) separation 

F = 50
L = 67
For 28 mm slide mount apertures:
R(A=76.875 mm) =  339 mm min, infinity max
For 31.5 mm slide mount apertures:
R(A=73.375 mm) =  525 mm
R(A=69.125 mm) = 1576 mm

F = 100
L = 67
For 28 mm slide mount apertures:
R(A=76.875 mm) =  678 mm min, infinity max
For 31.5 mm slide mount apertures:
R(A=73.375 mm) = 1051 mm
R(A=69.125 mm) = 3153 mm

John B

PS: You can mount to infinity with this set of specs under almost 
any conditions; you are not forced to mount to the window.


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