700 



HANDBOOK OF PHOTOGRAPHY 



shown in Fig. 43. This is a contact printer, i.e., a printer in which the negative and 

 positive pass through the same gate together. Contact printers are of two kinds : step 

 printers and continuous printers. The step printer resembles the camera and the 

 picture projector in that the two films are carried past the printing aperture and the 

 positive is exposed through the negative frame by frame, a shutter being used to cut 

 off the light while movement is taking place. The exposure is controlled by variation 

 of the light. This type of printer has a straight gate. In the continuous printer, as 

 the name indicates, the movement of the two films past the aperture is uniform. 

 Exposure may be varied by changing the width of the aperture or the intensity of 

 the light, the latter being more common. To reduce slippage between the two films, 

 the gate of the continuous printer is curved. The picture may be printed on either 

 type, but sound records can be printed only on a continuous printer. In making 



Fig. 4.3. — Picture printer. 



composite prints sound and picture may be printed consecutively, the picture being 

 masked while sound is being printed, and vice versa. However, combined sound and 

 picture printers are now in extensive use for making composite prints; these have twin 

 mechanisms and optical systems to permit the positive film to be exposed successivelj'' 

 to sound and picture in one operation, the light being adjusted in each case to the 

 proper intensity. This adjustment is usually made automatically by electromagnetic 

 control devices actuated by notches in the edge of the film or bj'^ traveling mattes in 

 the shape of auxiliary films. 



In the development of prints a constant gamma is maintained much as in the case 

 of negative. Sensitometric strips exposed on positive stock are developed at regular 

 intervals in each positive developing machine, and the time of development adjusted 

 accordingly. The positive bath must be replenished in the same manner as the nega- 

 tive bath. 



Printing exposure is in steps, one step, or point, being equivalent to 0.05 log E. In 

 the better maintained laboratories, the positive gamma is maintained to within ±0.05, 



