STEREOSCOPIC PHOTOGRAPHY 



593 



Fig. 12.— 

 Diagram of 

 wide-angle lens 

 system for ster- 

 eoscopes. 



manner such stereographs have no technical value whatever, as the resultant depth is a 

 completely false one. The object shows no depth within itself. 



Cloud stereographs can be made in the same manner, provided there is some 

 lateral motion of the clouds without an accompanying change of shape. The farther 

 the clouds move between views the nearer the earth they will appear. 



The possibility of applying stereography to other astronomical phenomena are 

 extremely limited. They certainly are restricted to the solar system. The maximum 

 possible base is twice the distance of the earth from the sun or 186,000,000 miles. 

 From formula (3) this means that a star would have to be within ^2 light year of the 

 sun to show any relief against an infinitely distant background. The nearest star is 

 greatly in excess of this distance. This shift is, of course, used to 

 measure the distance of near stars, as a much smaller angle can be 

 measured than the eye can detect in a stereograph. 



Wide-angle System. — The angle of view of a normal eye runs to 120° 

 or more. The average stereoscopic camera covers an angle in the 

 neighborhood of 60°. This imposes a restriction on stereographs 

 which detracts from their reality. 



A lens system is available which satisfactorily increases this angle 

 up to 90°. The system is practically free from chromatic aberration 

 and is corrected for distortion. It involves two lenses as shown in 

 Fig. 12. Complete technical information on this system can be found 

 in L. E. W. von Albada, A Wide Angle Stereoscope and a Wide Angle 

 View Finder, Trans. Optical Soc. {London), vol. 25, no. 5; and in A. 

 W. Judge, "Stereoscopic Photography." 



Pseudoscopic Views. — If the two views of a stereograph are trans- 

 posed so that the right eye sees the left view and vice versa, a pseudoscopic view results. 



If the stereograph is of separated objects the order of depth of these objects is 

 reversed, i.e., the background objects appear in the foreground and vice versa. 



If the stereograph is of a simple geometric figure or of such a nature that the solidity 

 of the object can be reversed without destroying its meaning, such reversal will occur. 

 Thus a pseudoscopic stereograph of the pyramid in Fig. 1 would appear to be a pyramid 

 with the base in the foreground and the apex in the background. 



In normal scenes including persons, buildings, or landscapes, the pseudoscopic 

 stereograph leads only to confusion as the depth factors indicating the true scene are 

 opposed to the pseudoscopic factor. Confusion and loss of depth are the result. 



Bibliography 



The Hterature of stereography is extremely limited. The following list contains the most important 

 works on the subject; 



Periodicals: 



Wheatstone, Charles: Contributions to the Physiology of Vision, Phil. Trans. {London), (1838). 



French, J. W.: Stereoscopy Re-stated, Trans. Optical Soc. {London), vol. 24 (1922-1923). 



Albada, L. E. W. von: A Wide Angle Stereoscope and a Wide Angle View Finder, Trans. Optical Soc. 



{London), vol. 25 (1923-1924). 

 Trump, R. W.: Binocular Vision and Stereoscopic Sense. Trans. Optical Soc. {London), vol. 25 (192.3- 



1924). 

 Kurtz, Henry; Orthostereoscopy, /. Optical Soc. Am., October, 1937. 



Much of the literature has been in the form of short articles. Some of these have appeared in the 

 following journals: 



Philosophical Magazine- 

 Photo Miyiiature. 

 American Photography. 

 British Journal of Photography. 



