Three-Dimensional Photography - Principles of Stereoscopy

190 THREE-DIMENSIONAL PHOTOGRAPHY

focus of the two lenses may be accurately matched under all con-
ditions. These lenses are coated, and may be obtained in different
focal lengths to provide for different distances of projector throw.
The slide changer blanks out the screen while changing slides,
and does not show the picture until the slide is in place. The slide
moves between a top and bottom vee goove so that slides of vary-
ing thickness can be accommodated, A spring at the top pushes the
slide down into contact with the bottom of the carrier to maintain
an even base. The insertion of a fresh slide pushes the first one
into position where it may easily be grasped for removal. This pro-
jector will give excellent service and through some two years serv-

Fig. 12-2. Realist projector, companion to the

Realist camera, projects the standard 35mm

stereograms.