704 



HANDBOOK OF PHOTOGRAPHY 



Characteristics) and accurately registered prints free from excessive grain, dirt, 

 scratches, etc., which would tend to show up in the final picture. 



The principal implement of aftertreatment is the optical printer, shown schemati- 

 cally in Fig. 46. The printer head on the right is essentially a lensless projector equip- 

 ped with a 500- or 1000-watt light source, providing uniform, diffused illumination at 

 high intensity. It is usually a rebuilt motion-picture camera fitted with a registration 

 or pilot-pin movement and mounted on a lathe bed opposite the photographing camera 

 on the left, which is likewise equipped with a registration movement. Camera and 



Foreground li'gh / 

 (whi'-f-e) ^^ 



S-fandard 

 camera 



/ 1 

 Camera afigje / 



Trans lucerr^ 

 screen y 



Projecior synchron- 

 ized and phased 

 wi'ih camera , 



ProJecTor ^cj | 



angle 



Foreground ac+i'on 

 Fig. 45. — Composite photography by rear-projection method. 



printer head are driven in exact synchronism from a common shaft. While the image 

 in the printer head is moving, the camera shutter is closed; exposure occurs while both 

 films are stationary. The lens shown between the camera and the projector is designed 

 for unit magnification; it may be an ordinary camera lens stopped down to//8 or//ll, 

 although lenses especially corrected for photographing at short distances are preferred. 

 Exposure may be controlled hy altering the intensity of the printer light, the lens 

 aperture, the shutter opening, or, in special cases, the speed of printing. The speed 

 depends mainly on the work being done, 40 ft. per min. being about the maximum and 



ior 



bate confaining frame , Special proJecTo 



of f/lm being phoi-ographed i or prinfernead 



-l/ghf 

 source 



Lai-he bed-' Unii magnlficaHon lens 



Fig. 46. — Schematic diagram of optical printer. 



18 ft. per min. an average figure in practice. Provision is made for driving each unit 

 forward or backward, mechanically or by hand, at the same or different speeds. With 

 differential operation two or more camera exposures may be made of each image frame, 

 slowing down the action, or one exposure may be made of every alternate or third 

 image frame, speeding up the action. Rewinding is usually done at 90 ft. per min. 

 Both the camera and projector may be moved laterally or vertically as well as along 

 the lathe bed, or in place of the lateral and vertical movement of these units, the lens 

 may be moved to adjust the picture. Special movements, such as rocking the camera 

 during operation, may be employed to simulate the rolling of a boat, etc. 



