6 THREE-DIMENSIONAL PHOTOGRAPHY
but care is taken to make sure the camera rests solidly against
one of the side rails and against the rear rail. In other words, the
camera is pushed into one corner of the rails. The exposure is
made as usual, erring if at all upon the side of overexposure.
The camera is then pushed sidewise until it rests firmly in the
opposite corner, and the second exposure is made.
As the negatives must later be cut apart and rejoined to estab-
lish the correct spacing, it is immaterial which exposure is made
first.
OTHER TYPES OF BASE,--StereO shifting bases are obtainable
from many dealers. They may be the simple sliding] type, as for
Fig. 1-3. A Rolleiflex camera mounted up-
on a Rolleiflex stereo slide bar for making
stereograms by successive exposure.example that sold for use with the Rolleiflex camera (Fig. 1-3),
or it may be the parallel-arm type made popular in Germany.
An examination of the latter shows its construction so clearly