Re: realist or Pentax stereo adapter

[P3D Greg Erker <erker@xxxxxxxxxxxxxx>]

Realist vs Pentax Stereo adapter for face research:

  I own both but don't know which would be best for your
application. But here are a few thoughts.

  In 2d photography 85 to 100mm is said to be a good portrait
lens so that you don't get the big nose effect that wide angle
lenses give. Thus a 50 or 55 mm on a PSA would be better than
the 35 mm of a Realist. An RBT with the zoom lenses (at the
long end) would be even better, but is big $$$. The RBT has
the lenses further apart than eye spacing, so would make
people look somewhat smaller (not sure how much).

  The Realist and Pentax probably have enough resolution that
you could shoot portraits at the distance you would use with
a 100 mm lens. Then you can crop them to head shots after
digitizing. With slow film you still would probably have
enough resolution for 1500x1000 pixels, or whatever you need.
This gives you the perspective of a portait lens without having
to buy one.

  The PSA and all beamsplitters have some keystone distortion
but it is somewhat corrected by the viewer. For your application
the keystone would remain and may cause problems.

  You should have viewing lenses of the same FL as the camera
taking lenses to avoid strech or squash in the Z direction. I am
not sure what this means as far as a monitor but you probably
want to have an ortho setup (or close to it) to avoid Z
axis distortions that may invalidate your study.

  The PSA has the dark bar in the middle. But even away from
the bar, portions of the image are darker in one eye than the
other because of being closer to the center bar. This causes
a sort of retinal rivalry that reduces realism of the slide.

  The PSA also doesn't give you a proper stereo window but this
could be fixed in the digital domain.

  To avoid yet another Realist vs BS thread I'll say that these
are only my opinions and only applies to the use under discussion.

Greg Erker (proud poster of the info about the $30 Virtual Boys)





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