54 



TROUBLES WITH THE MAGIC LANTERN lCn 1 



FIG. 28 (A). DIAGRAM SHOWING THE EFFECT ON THE SCREEN IMAGE 

 WHEN THE RADIANT is TOO NEAR THE CONDENSER. 



In this case the conjugate focus of the condenser (/) is considerably farther 

 off, i. e., beyond the objective, the screen image is made smaller, and the light 

 disc on the screen is bordered with blue. With some condensers there is a 

 dark or blue disc in the center also. (Lettering as in fig. 26). 



FIG. 29 (B). DIAGRAM SHOWING THE EFFECT ON THE SCREEN IMAGE 



WHEN THE RADIANT is BEYOND THE PRINCIPAL Focus 



OF THE CONDENSER. 



This brings the conjugate focus of the condenser (/) nearer the condenser, 

 and in this case just before the light reaches the objective. It narrows the 

 screen image and the light disc is bordered with red. (Lettering as in fig. 26). 



the axis, but the blue spot or disc will be on the side away from 

 which the condenser is displaced, being just the reverse of the 

 position when the light source is off the axis ( 83). 



If the condenser is too high the blue spot or disc will be on the 

 lower part of the screen; and if the condenser is too low the blue 

 edge will appear on the upper part of the screen ; if to the right the 

 blue disc will be at the left, etc. That is the condenser inverts the 

 position (fig. 27). 



The condenser should be correctly centered once for all and 

 firmly fixed in position so that it need never be changed. 



85. The projection objective may be off the main axis. The 



effect will be the same as when the source of light is off the axis. 

 This is due to the fact that while the condenser inverts the rays, 



