CH. XI] 



OPTICS OF MOVING PICTURES 



411 



get a good light on the 

 screen must now be taken. 

 The moving picture head 

 as it comes from the fac- 

 tory should have the 

 aperture plate and the 

 center of the objective 

 mount at the same 

 height. If they are not, 

 the aperture plate must 

 be moved up or down 

 until its center is on the 

 same axial line as the ob- 

 jective. The adjustment can prob- 

 ably be done with sufficient accuracy 

 with the eye, when looking through 

 the lens opening, the lens being in 

 place. This is a matter which al- 

 ways should be looked after by the 

 manufacturer. 



Another method would be to re- 

 move the condensers and adjust the 

 arc lamp to exactly the same height 

 as the aperture plate. A piece of 

 paper put in place of the lens 

 should, when the arc is lighted, 

 show the shadow of the center of 

 the aperture plate in the exact cen- 

 ter of the circular piece of paper. 



FIG. 228. OPTICAL SYSTEM AND ILLUMIN- 

 ATION OF MOVING PICTURES. 



Lamp. 



Condenser. 



S Lantern-slide holder. 



Fire Shutter This is open only when 

 the machine is running. 



s Aperture plate. 



Objective. 



See fig. 231 for full explanation of the 

 mechanism. 



