584 



HANDBOOK OF PHOTOGRAPHY 



The advantages of this system are (1) the two views may be superimposed, thus 

 allowing prints of any size to be used; (2) the space is only one-half that used for the 

 same size in other systems; (3) the spectacles may be simple cellophane masks and 

 consequently flat and very cheap. 



These facts make the system the best for publication work. Numerous magazines 

 have published anaglyphs inserting masks in each copy of the issue. The system has 

 been, and is, extensively used in aerial photography publications. 



The disadvantages of the system are (1) the difficulty of getting proper dyes, (2) 

 the great absorption of light through the masks, (3) the inherent impossibility of mak- 

 ing colored stereographs, (4) the green and red colors do not fuse into white around 

 the edges of objects against a light background, but (5) leave an edge of color over 

 that part of the background which is obscured by a foreground object in one of the 

 views but not in the other. 



- Grounc^ glass 

 -Righ+ view 

 -V Pofaro/d 



Ground cf I oiss — •' ] j 

 Leff view — '''/ 

 H Polaroid ^ 



-CHatf 

 silvered 

 mirror 



\ 



\l 

 lefl-eye o 



\ / \ / 



© Right eye 



Fig. 8. — Stereo viewing device using polarizing plates. It is necessary for the observer 

 to wear polarizing glasses to obtain the fusion of images. 



Negatives used for anaglyphs should be very sharp for satisfactory fusing. Stop- 

 ping down the lens aperture is consequently recommended when making negatives for 

 this purpose. 



In viewing an anaglyph the plane of the paper is usually obvious. The best 

 impression is received if the scene seems to stand out from the paper rather than recede 

 into it. This is achieved by printing so that correspondingly distant points in the two 

 views are coincident in the superposition. If foreground points are coincident, the 

 scene will recede into the paper. 



Polaroid System. — A very convenient, recently developed form of viewer involves 

 the use of Polaroid, a material which polarizes light. This viewer is shown in Fig. 8. 



The H and V are sheets of Polaroid mounted at right angles to each other. They 

 polarize the light from the two lamps horizontally and vertically, respectively. The 

 transparencies representing the right and left views are inserted between the ground 

 glass and the Polaroid. The sheet C which makes 45° angles with the Polaroid sheets 

 is a half-silvered mirror which transmits one-half the incident light and reflects one- 



