582 



HANDBOOK OF PHOTOGRAPHY 



Stereoscopes for Roll Films. — Small full-lens type stereoscopes are also made for 

 (ise with standard-size motion-picture films. The Tru-Vievv Co., Rockford, 111., 

 manufactures one of these in America. The prints are small, so that it is possible to 

 interlock them. The first and fourth, third and sixth, fifth and eighth, seventh and 

 tenth, etc., views being paired. The second view is a blank never appearing before 

 either lens. A roll of films is fed through a vertical slot at the right side of the viewer. 

 A lever shifts the films the requisite distance. The stereoscope is of the box type with 

 a fixed focus. The films are positive transparencies. 



Z 670^ eye 



Righi- eye 



j< Focal lengih 



Fig. 5. — Stereoscope using split lenses. 



Fig. 6. — Mirror stereoscope, as originally used by Wheatstone. 



Leica also manufactures a stereoscope of this type already mentioned under 

 stereoadaptors. 



Lens-type stereoscopes should be fitted with side shields to eliminate stray light 

 around the eyes, a shield between the two views to render them mutually exclusive, 

 and a sliding plateholder or lens adjuster for focusing. If for use with transparencies, 

 they should completely exclude all light except that coming through the ground glass. 



Mirror Stereoscopes. — There are many types of mirror stereoscopes possible. In 

 all of them the two views are superimposed by reflection. 



The original mirror stereoscope was that of Wheatstone shown in Fig. 6. 



The two prints are mounted facing each other at A and B and are reflected into the 

 eyes from the mirrors C and D. The prints may be moved together or apart by means 

 of the screw. 



