ELEMENTARY STEREOGRAF’HY Ithat no further description is necessary. This type may also be
made at home, although more care is needed than in the construc-
tion of the board type.
STEREO hFLEcTom--The disadvantage of all “successive” types
of stereo exposure is that the object must be quite motionless
during the whole interval of both exposures. Because even the
slightest sway resulting from a breeze will effectually ruin the
result, this method is hardly practical for most exterior subjects.
The alternative of a stereoscopic camera is not always feasible
because of the necessarily greater cost of such instruments. To
meet this need, the stereo reflector was invented by F. A. P.
Barnard in 1853.
The stereo reflector is an arrangement of four reflecting sur-
faces which are set before the lens of any standard camera. This
divides the negative area into two portions, each of which receives
one of the stereo images. In the cheaper forms, the device is made
up of four mirrors, while the more elaborate types have two
prisms, each of which provides two reflecting surfaces. The prism-
type is fixed for one set of optical factors as embodied with some
given lens and camera, while the mirror-type may be so designed
that it may be adjusted for use with a variety of cameras and
lenses.
The Leica Stereoly is an excellent example of the prism re-
flector designed for use with the Leica camera, but easily adapted
to any miniature camera using a two-inch lens. The Stereotach
(Fig. 114) is an example of the mirror reflector of fixed adjust-
ment. Unfortunately there is no adjustable reflector available at
the present writing, although the Rexo stereo ada$ter which had
a full range of adjustment was sold about 1915.
These devices are attached to the camera lens in much the same
way that a filter or sunshade is attached. They require some
increase in exposure, the exact amount depending upon the de-
sign of the reflector used. Ordinarily, a three- or four-times
exposure is about right. Care should be taken that the mirror
division is exactly vertical and that it exactly bisects the lens.
Other than this, operation is normal and the results are highly
effective.
There has been a great deal of criticism offered regarding
these attachments. Tests of all types mentioned have indicated