Re: 2-camera stereo

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Thu, 20 Jun 1996 23:39:30 -0500
>From: P3D Neil Harrington  <nharrington@xxxxxxxxxxxxx>

>I haven't yet used a two-camera system.  I can see it would have advantages
>all right, as you say, for hyperstereo.  With practically any 35mm cameras
>on the market now it wouldn't really give you any _choice_ but to accept a
>certain amount of hyperstereo, since the camera width is bound to be greater
>than the usual lens separation on a stereo camera.  But that probably isn't
>a problem in most cases.  

I have a pair that I usually keep mounted for about 6" separation. (That's
slightly greater than the width of the cameras - I wanted to be able to
open the backs of the cameras without removing them from the bar.)

It's usually possible to mount base to base, and take the pictures in a
vertical format (that works for stereo prints, anyway). The problem is that
if you have focal plane shutters and take photos in bright light, the shutters
in the two (base to base) cameras are moving in opposite directions, so only
a tiny fraction of the image is actually in sync. (Of course that doesn't
matter for subjects that don't need fine synchronization of the two images.)

>I've done some single-camera stereo, shifting the
>camera sideways for the second shot, and this always seems to work out fine
>at moderate distances, even with no attempt to be really precise about the
>distance of the shift.

I agree.

>I'm assuming, of course, that the lenses would be close enough not to require
>any special matching.  

I've never had any problem, though I'm usually careful to buy new equipment at
the same time, from the same source. I don't know about the specific cameras
you mentioned.

As previously noted, there is no "stereo window" in a 2-camera system
(equivalent statement: the stereo window is set at infinity). But humans
were seeing in stereo for millions of years before the invention of the
stereo window, and a little trimming allows the user to impose a stereo
window at whatever distance desired.

John R


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