578 HANDBOOK OF PHOTOGRAPHY 



As short-focal -length lenses have more depth of fociis and the distance beyond which 

 everything is in focus is less than in lenses of long focal length, shorter focal lengths are 

 preferable for stereoscopic work. Several methods of making stereographs with a 

 single camera are possible. 



Camera May Be Shifted between Exposures. — If the distance to the object is small, the 

 camera should be pointed at the same spot near the center of the object in both views. 

 If the distance to the object is greater than 6 ft. a simple lateral displacement is all 

 that is required. 



The distance between the two positions of the lens should be about 2 '^'2 in. unless a 

 hyperstereoscopic effect is desired. 



The lens nuist be at the same distance from the object in both views. 



The camera should be at the same elevation and level in both views. 



The stops and lighting conditions should remain the same. 



Many devices can be made to aid in shifting the camera (see "Stereoscopic Photog- 

 raphy," A. W. Judge). For cameras with flat bases, such as the box types, a tray may 

 be constructed, the width of the tray being equal to the width of the camera plus the 

 interocular distance. It is then necessary only to push the camera against the opposite 

 ends for the two views. 



A rigid frame may be built around the camera which slides in another frame and 

 locks in the proper positions. 



Some manufacturers (Leica, Rolleiflex) furnish devices for this purpose. In gen- 

 eral these are constructed to fit between the tripod and the camera. They either swing 

 or slide the camera the requisite distance. Leica ^ furnishes a Stereo Slide Bar which 

 permits the camera to be locked in any position up to a separation of 15 cm., thus 

 permitting the taking of hyperstereoscopic views up to that maximum base. 



The Object May Be Shifted the Interocular Distance. — The object must be against 

 a plain background with no other objects in the view unless such objects are also 

 shifted. 



The shift must be level and perpendicular to the axis of the camera. 



The object should not be much closer than 6 ft. from the camera. At shorter 

 distances the camera should preferably point to a spot between the two positions of 

 the object. 



The light should preferably be uniform, not from a concentrated source. 



The stops and the lighting conditions must remain the same. 



This is a convenient method for photographing small objects that are easily shifted 

 on a table. 



The Object May Be Rotated. — This is a more accurate method than shifting the 

 object particularly for short distances between the object and the camera. 



The object should be against a plain background. If it is not or if other objects 

 not rotated around the same center also are in the view, the background and these 

 objects will show no relief in the stereograph. 



The proper angle of rotation for orthostereoscopic views can be calculated from 

 the formula : 



a = 2 sin-i (~) (4) 



A greater rotation gives a hyperstereoscopic effect. 



A simpler method of rotation is to pick out or mark two points on. the object in 

 line with the lens of the camera and the center of the object. Then rotate the object 

 until a line through these same points passes 2^2 in. to the right or left of 

 the lens. 



' See Leica Manual. 



