Custom 3D video cameras

[P3D Ray Hannisian <ray3d@xxxxxxxxx>]

Dear Group,

For the past several years, I have been shooting 3D video with a home made
system.  It consists of two genlocked SONY DXC-151A cameras component
multi-plexed to a Hi-8 recorder, (actually a SONY EVO-9100 in VCR mode).
The power supplies, controls, monitoring and audio solutions are hacked from
surplus equipment.  Most of the gear rides in a backpack, with the cameras
mounted on a slide bar which can be placed on a tripod, hand carried or
positioned on a ski helmet.

I have observed that keeping the cameras truly parallel creates problems
with the "stereo window" during playback on TV monitors and VR headsets.
This is due to the fact that the physical position of the TV set in a room
is visable to the person viewing it, as are the edges of the "window" in
headsets.  Stereoscopic IMAX, on the other hand, uses perfectly parallel
cameras, but for all practical purposes doesn't even use the screen during
projection, since the image fills one's entire view.  

My solution to the "window problem" is to 'toe-in' the cameras, creating a
convergence point which varies according to the subject matter I am
shooting, the interocular positioning of the cameras and whether or not a
distant background is visable in comparison with close-up objects.  The
distortions created by this procedure are better than having infinity
objects appear in front of the TV screen, and having unresolvable edges.

"Stereographics Corp." uses electronic circuitry in their products to
produce a 'side-slipping' of the images to create what they call
"coincidence", rather than "convergence".  This is equivilant to shooting
film with parallel cameras and positioning the convergence (coincidence)
point during mounting.

I am looking for a mechanical solution.

I would like to separate the lens-boards from the cameras in such a way that
they may be offset sideways while remaining parallel to the CCDs, as is done
in 4x5 view cameras.  A small screw adjustment should make it possible to
'dial' the correct displacement.  A bellows arrangement would keep it
'light-tight'.  


I would appreciate advice from anyone with some optics background on the
following matters:

When dealing with sideways displacement, will a standard lens provide
coverage outside of its normal target zone?  (I've always thought that view
camera lenses were built to cover more area than a non-movable lens.)

Will 'side-slipping' my lenses create a different F-stop, (reducing the
amount of light reaching the target)? 

Should the lenses retain the original inter-occular distance, and the
cameras be displaced, or vice versa?  (My intuition leans toward the lens
positions determining the correct spacing.) 


For the moment, this is only a hypothetical camera system.  However, I
eventually wish to build a portable Betacam SP video system based upon two
Toshiba IK-TU40A 3-chip miniature cameras and a SONY BVV-5 recorder.  I
imagine it having variable inter-occular spacing, convergence and
coincidence and synched zoom lenses.  

Any suggestions or comments would be welcome.

Thank you.

Ray Hannisian
 
   ====== Ray 3D - Stereoscopic Imaging ======
                  ray@xxxxxxxxx
              http://www.ray3d.com

        Director: 3D Photo and Video Group
                   VRex, Inc.
                 ray3d@xxxxxxxx
Date: Fri, 11 Oct 1996 12:46:19 -0500
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