STEREOSCOPIC PHOTOGRAPHY 



579 



All the above methods demand that the scene be motionless for the time required 

 to change the film or plate and to reset the camera or object. 



Use of Ste?-eoadapter. — By the use of a stereoadapter a stereograph with a single-lens 

 camera and a single exposure can be obtained. This permits moving objects to be 

 photographed. 



Such adapters consist of arrangements of mirrors or prisms designed to bring the 

 two views into the left and right halves of the lens, respectively. Figure 4 shows the 

 simplest arrangement of mirrors for accomplishing this purpose. 



A distinct advantage of such adapters lies in the fact that the refraction through 

 the lens reverses the views so that they 

 appear in proper position upon the nega- 

 tive and do not have to be transposed. 



Leica manufactures a stereoadapter, 

 called a Stereoly, using prisms. The device 

 fits in front of the lens. It divides the 

 standard 36- by 24-mm. picture into two 

 of 18 by 24 mm. A special viewer for rolls 

 of films of this type is also furnished. 



The use of a stereoadapter involves a 

 great reduction in the amount of light reach- 

 ing the film. Splitting the lens cuts the 

 intensity to one-half, while the absorption of 

 prisms or mirrors further reduces it. Con- 

 sequently longer exposures are necessary. 



The camera should be of such a type 



Cctmeroi lens 



V 



/\ 

 / \ 

 )^ \ 



Fig. 4. — Simple arrangement of using 

 two sets of mirrors to provide stereoscopic 

 effects with a single-lens camera. 



that the film used in it can be divided into two areas which are approximately 

 square. 



Stereographs with Two Cameras. — If cameras are small, two may be clamped 

 together so that the lenses are separated by 2H in. or slightly more. This means that 

 the plates must not be larger than 2I2 in- in width. If the separation between lenses 

 is greater than 2H in., a hyperstereoscopic effect results. 



Care must be taken that the following conditions are fulfilled: 



The lenses must be well matched. The manufacturer should be willing to do this 

 when the cameras are purchased. 



The line between lens centers must be level with the resultant base of the combined 

 cameras. 



Indicated equal shutter speeds and diaphragm openings must be in reality equal. 

 In cheap cameras there may be considerable variation in shutter speeds causing a 

 difference in exposure times. 



The shutters must work simultaneously. Leverages or connecting bars must be 

 designed for this purpose for the particular cameras to bemused. 



With inexpensive cameras this affords a very cheap and satisfactory method of 

 making stereographs. The beginner who cares to experiment with stereoscopic 

 possibilities will do well to start in this manner. 



Double-lens Cameras. — A stereoscopic camera with two matched lenses separated 

 by the interooular distance permits the taking of stereographs of any type of scene in 

 exactly the same manner that ordinarj^ photographs are taken. As long as the shut- 

 ters, focusing devices, and diaphragm openings are each linked together and each set 

 by one adjustment, the operation is no different from that of the usual camera. 



Most stereoscopic cameras are fitted with lens caps so that one lens may be covered 

 if it is desired to take single pictures or hyperstereographs. In the latter case the right 

 lens is covered for the right view while the left lens is covered for the left view. The 



