412 OPTICS OF MOVING PICTURES [Cn. XI 



The center of the condenser and the center of the aperture plate 

 are adjusted to the same height above the baseboard. This is 

 attended to by the manufacturer, but if a head of one machine is 

 used with the arc and condenser of another make, adjustment 

 might have to be made. Make a spot with a pen or a wax pencil 

 exactly in the center of the front lens of the condenser, measure the 



height of this above the baseboard. 

 Make a similar mark on the aperture 

 plate at the height of the middle of 

 the opening and measure its distance 

 above the baseboard. If the aperture 

 plate is too low the head should not 

 be screwed directly to the baseboard 

 but should be lifted U P sufficiently with 

 (Cut loaned by the Gundlach- a thin piece of board. If the aperture 

 Manhattan Optical Co.). plate is too high( the front of the base . 



board can be cut down or the lamp-house and condenser can be 

 raised by using a piece of wood or asbestos board between the base- 

 board and the lamp-house fastenings. 



After getting the objective, aperture plate, and condenser at the 

 correct height, it only remains to get the arc at the right height. 

 This is done from time to time by raising or lowering the arc lamp 

 until the light spot falls exactly over the aperture plate. 



The sidewise adjustment of the lamp-house is now made in the 

 same way by measuring the distance from the edge of the base- 

 board to the center of the condenser and then to the center of the 

 aperture plate. This measurement can be made by using a vertical 

 board (52). 



When the same arc and condenser are used for both moving pic- 

 tures and lantern slides, the lamp-house should be in the correct 

 position when pulled on its lateral rods as near as possible to the 

 operator. If it is not, stops can be fastened on the side rods to hold 

 the lamp-house in the correct position. 



578. Back and forth adjustment of the arc lamp and con- 

 denser. This is one of the most important and troublesome adjust- 

 ments to make. There would be but little difficulty in getting an 



