276 THREE-DIMENSIONAL PHOTOGRAPHY
be seen upon the screen when using the 3-D viewers. If you have
the filters in rotating mounts, you can easily make the adjustment
while the picture is on the screen.
Remember, the screen MUST have a surface which does de-
polarize light, the most convenient being the aluminum surface.
Ordinary beaded screens will not work. You will see both images
no matter whether you use the goggles or not.SUMMARY OF ESSENTIALS
The most satisfactory stereo accessories for movie work must be
home made. This is a condition we hope will soon be remedied.
The compressor lens, if one is found, is simply placed before
the camera lens. Be sure to use the guide line so that the com-
pression is accurately lateral, and be sure to focus the compressor
using the engraved scale. Otherwise it is simply an accessory lens.
The reflector must be set for the lens in use, and so adjusted
that the images are equally and symmetrically divided between
the two halves of the aperture.
Use a wide base when using lenses of more than normal focal
length. Use twice normal base for a two-inch lens and so on.
Use exposure compensation because of losses in both reflector
and compressor. About three times to four times is advisable.
Use the whole unit, compressor and reflector upon the projector
and add the polarizing filters.
Superimpose images upon the screen, preferably with the ad-
justable reflector.
Do not get too close to the screen.
Otherwise, use normal movie procedure.
Many amateurs who have expected some very difficult and very
complex procedure may think this too easy, but like all stereo, it
is as easy as normal photography once the necessary equipment is
available. If you consider the general laws of stereo and the re-
marks concerning still stereo projection together with this chap-
ter you will be fully prepared to embark in making stereo movies,
and very often your first film will be fully successful. Starting
from scratch some 14 years ago, we made one film which was
slightly distorted as to depth-width relationship, but the second
was good and no more trouble has been encountered.
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