P3D Vertical Mounting Standards and Projection

[LeRoyDDD@xxxxxxx]

Brenda N., following an enjoyable evening of 3D at a PSSP meeting, said:

"After the first show (these were slides taken by PSSP members) Mr. Duggin
tried to explain the importance of mounting properly and consistantly by
standards set for stereo photography.  He threatened that in the future there
would be no more adjusting of the projector.  Either mount properly by set
standards or suffer the consequences.  A few members argued that you could
not be consistant because viewing situations vary.  For example one person
said that if you mount to project in your living room the same slide would
not work for a larger room where the projector would be farther away.
 Someone else said the size of the screen would make a difference."

     Every slide should be projection mounted. End of Story.

     Well, actually, the Story just begins... the minimum mounting
requirement is that a vertical disparity of zero(with respect to the mount
window) be aimed for.
     This is important for viewing, too.
     With my "rubber 3D eyes" and tolerance for pain in the pursuit of
viewing stereo, I'll personally tolerate a lot of inaccuracy here, but _will
not_ subject others to a hastily(poorly) mounted slide.
     Modern precision mounting materials make good verticals
automatic(almost) if the film chips come from a "real" stereo camera. If the
camera has minor built-in vertical disparity, modern mounts will allow
adjustment. If the image sizes are different, though, one cannot get zero
verticals throughout the scene.
     Often, what is thought to be vertical misalignment is "twist" between
the chips, especially from rotated separate camera setups or "rock and roll"
shots. (Don't know of any projector[for coupled pairs] that has a twist
adjustment!)

     What you can't control...
     1) The projectionist "set-up" slide may be different than your mount.
Slide mounts vary. Also, if the mask and mount are not integral, their edges
may not be aligned.
     2) Depending on the projector and the projectionist technique, one side
of the slide may be higher than the other in the projection path.
     3) Incredibly, the projectionist may have corrected bad verticals in the
slide just before yours and your perfectly aligned slide is now projected out
of alignment!
     4) Cardboard mounts may be worn or buckled... in additions to more
variability between brands of cardboard mounts, this is another reason _not_
to use them.

     So if I'm projecting(not enjoying :=( ), I'd align with my setup slide
and evaluate images(unpolarized) as they came up for vertical errors. If any
had more vertical error than I felt was OK for the image size, I'd just
quickly go to the next slide.
     Depending on the situation, I'd announce "verticals" or "twist" or some
such formulation. If I though my technique had caused the error, I'd save the
slide out for reprojection.
     The vertical adjustment on the projector would not be touched.

     The size of the projected image on vertical tolerance is of little
consequence as the bigger the image the further back the audience(except for
ortho fanatics!). For example, a vertical error of one inch on a six foot
screen viewed from seven feet is of the same effect as one of two inches on a
12 foot screen viewed from 14 feet.

LeRoy Barco
LeRoyDDD@xxxxxxx


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