[photo-3d] Franka beamsplitter/stereobase/blessed event

[Mark Shields <beamsplitter@xxxxxxxx>]

Fascinated by recent discussions of stereobase, especially
the concept that for smaller formats (and the half-frame
beamsplitter format certainly qualifies) a larger stereobase
(or on-film deviation, if you prefer) is better, to give
a stronger impression of stereo to the viewer, and bolstered
by the realization that I would just have to stick to the
beamsplitter format due to the reduced time available for
stereo photography (read: time to mount Nimslo or cha-cha
pairs, which are much harder than beamsplitter), I did the
following:

I finally removed the second-surface mirrors from my Franka
beamsplitter, which I got from Steve Berezin, and into which
I now plan to install the first-surface mirrors which I got
from David Lee. (I for a brief period flirted with the idea of
running a test roll of Provia 100F through the camera with the
second-surface mirrors, just to see how it would do, but decided
to stick with replacement front-surface mirrors and Kodachrome.)

Not only did I catch the concept of increased stereobase beyond
70mm (the Franka supplies 110mm), but I realized that, for
scenery, a larger stereobase is better anyhow, even if you
don't use a telephoto lens (I'm ultimately hoping to modify
the Franka to use an 85mm lens, which will require cutting out
its plastic housing so I can use toe-out on the mirrors).

I'm going to work carefully and clean the mounting surfaces
carefully before I apply Weldwood contact cement to the mating
surfaces before installing the new mirrors.

The old mirrors did not have nearly so aggressive an adhesive
as I had feared--I had visions of broken splinters of glass
(fragments of mirror) desperately adhering to the plastic
substrate!  :=(

In fact, the only tool I used was a medium large jewelers'
screwdriver. The moveable wings for the outer mirrors
(removed from the housing--two Phillips-head wood screws)
flexed, and gentle insertion of the screwdriver,
with gentle prying motions, removed them handily,
despite some frightening noises along the way. The inner
mirrors, on an also easily-removed opaque plastic prism,
were more difficult since the prism did not flex. But after
I splintered away a few fragments of glass at one corner,
(wearing protective goggles over my eyes!) the mirrors
separated from the plastic without shattering.

Would anyone like some surplus second-surface mirrors for the
purpose of applying cosmetics?  :-)

My thanks to Steve Berezin for supplying the Franka beamsplitter,
and to David Lee for supplying the front-surface mirrors. After
checking the new mirrors against the old ones, I found that his
cutting was extremely accurate, and I anticipate few if any
problems in installing the new mirrors.

I can't wait to see the pictures!

Mark Shields

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