278 THREE-DIMENSIONAL PHOTOGRAPHY
projector lens should also be shifted. When this is done, you will
have a complete and highly satisfactory 8mm stereo movie outfit.
16~~ CONVERSION.-The same thing can be done with a 16mm
outfit with less trouble because the lenses do not have to be
shifted.
The top or bottom half of the aperture is blocked off. For tem-
porary use, you can do this by pasting a bit of black paper over it,
from the shutter side. In most cameras, this can be done by re-
moving the lens and revolving the shutter until it opens. Do not
paste in the film side. The film will be scratched and will soon
pull the paper from its position.
Finally, mask the finder to correspond, BUT if you mask the
bottom of the aperture, mask the top of the finder. Then add side
masks to the finder so that 1/4 of the field is cut off at each side.
The area left is equal to 1/4 of the original.
The reflector is used with no compressor.
Only half the film will be exposed, and if you choose you can
use the same roll for a second series of exposures, if you remember
that sequences will be scrambled and editing will be impossible!
The reflector is used with the prqjector too, of course. In this
method, the actual film image has just the same size as in the
converted 8mm outfit, but the i6mm involves either double film
cost or the sacrifice of editing.
CoMPRoMrsE.-There is one compromise which is perhaps the
best of all solutions for the problem of format. The 16mm frame
is approximately 7.5 x iomm. If you wish to use a square aper-
ture, it will be 5x10 because there must be two pictures side by
side. Therefore instead of masking half the aperture you may
mask only 1/3. For the best possible results, you will divide the
2.5 mm mask into two parts. Mask off 1.25mm at the top and
1.25mm at the bottom. You will now have a centrally spaced
aperture measuring 5mm high and iomm wide. Your effective
aperture is 5mm square or 25 sq. mm. area. With either of the
former conversions, the effective frame measures 3.75~5 or about
18.75 sq. mm.
For the utmost gain commensurate with acceptable format,
mask imm from top and bottom leaving the total aperture 5.5~10
or an effective aperture five wide by 5.5 high, a ratio of 1o:i1,
roughly the same proportions as the Realist frame. This gives an