P3D the value of toe-in

[boris@xxxxxxxxxxxx (Boris Starosta)]

Friends,

I could not ignore Dave Spacey's question of several days ago because it
was so perceptive.  Add to that Dr.T.'s follow-up comment, and I realized
that I could no longer conceal the use of camera convergence in my work.
At this point, I felt that would have been dishonorable.

But why conceal my use of the technique until now?  Because it is "not
recommended," and I wanted to spare myself the inevitable criticism.

(For general information:  "toe-in" and "convergence" refer to a
non-parallel configuration using two cameras that are part of a twin rig.
In effect, each of the two cameras is pointed slightly inwards, towards the
other camera.  The resulting intersection of the optical axes in space some
distance from the rig, will form a stereo window for the pair of images
produced by the cameras.  The more the cameras are "toed-in", the closer
the stereo window.   An equivalent technique can be used when using a
single camera on a slide rail, or hand-held using the weight-shift method.
For those who missed Spacey's question several days ago:  After I said
that I did not need to remount my vertical format slide pairs, he asked
about how I set my stereo window - since shooting with a "straight" twin
rig places the stereo window at infinity on the slides as returned from the
processor.)

As it turns out, my very first pair of rolls was shot with no toe-in.  At
the time, I was only barely aware of the concept of the stereo window.
Because I was shooting a close up subject, my boy at a range of about three
feet, when I got the slides back I received a very blunt and emphatic
lesson in the functionality of the stereo window.  These slides were almost
unviewable, the window violations were so bad!  In those slides, had I
masked the film to produce a proper stereo window, I would have ended up
with a frame of only about 15mm width, and 35mm height!

I relate this story so that everyone understands that I am not using
convergence just to irritate the old wise men (and women) of stereo
photography.  I understand keystoning, and would certainly prefer to avoid
it.  But the fact is, if I shoot close up subjects with a vertical twin
rig, I HAVE to use convergence in the cameras to get a full frame 35mm
slide pair.  (That's not entirely true.  Given enough money, I could get a
pair of shift/tilt lenses to be used on 35mm SLR camera bodies.  I could
shift these "in" a bit, to create a stereo window "in camera" without
keystone distortion.)  It's also nice to get slide pairs from the processor
that are instantly useable in a viewer.

The reason I remount slides for competition is mostly because I have to
remount in Realist format frames.  Many 2x2 pairs do come back from the
processor with vertical misalignment.  If I send 2x2 pairs to an
Exhibition, these days I usually remount them to correct for this.  But it
is not always necessary.

Respectfully submitted,



Boris Starosta

usa 804 979 3930

boris@xxxxxxxxxxxx
http://www.starosta.com
http://www.starosta.com/3dshowcase

"The cut worm forgives the plough."
-Blake

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End of PHOTO-3D Digest 2597
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