S3D Re: Beam splitter options: please advise

[SHIELDS@xxxxxxxxxxxxxxxxxx]

What are usually called "beamsplitters" in stereo circles really
aren't--there have been optical devices, particularly in movie
cameras, that let part of the light go one way and part another
way, whether a prism device or a partially-silvered mirror as in
the Canon Pellix SLR. The common stereo beamsplitter divides the
35mm format (24X36) into two halves, each 18X24. It usually uses mirrors, 
although prism devices are out there.

Any stereo photograph requires that the camera be held level,
even if you are using a rail or slide bar for one camera and
shifting it from side to side. Most beamsplitters, since they
screw onto the front of a single lens, _do_ pose the additional
requirement that they must be parallel to the camera body.
An annoyance, to be sure, but one I'm willing to put up with.
The Pentax is a good unit and very expensive new, but it is
usually possible to find a good used one for less.

Reading your other post, however, I don't think you will be
happy with a common beamsplitter because it produces a vertical
format. It's certainly not for everybody. I have a lot of half-frame
experience and like the mild telephoto effect of a splitter on
a 50mm lens. This is not the prevailing opinion--most stereo
cameras produce an approximately square format using 35mm
lenses. If 7 perf isn't wide enough for you, and the stuff
at the edge is very important, you aren't going to be happy
with 4 perf, which is what you'll get with a Pentax splitter.

There was a really rare splitter on eBay recently--I think it's
gone now--that produced over-and-under images on 35mm film--
two images about 12X36--panoramic! I'm sorry but I don't 
remember too much else about it. You could hunt around and
ask questions if that's what you really want--research the closed
auctions on eBay.

Beamsplitters can produce excellent results if used correctly,
but you must understand and accept their strengths and limitations,
same as any other kind of equipment--will it really do what you
expect it to do?

Mark Shields

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