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HANDBOOK OF PHOTOGRAPHY 



Tables II and III contain data on the monochromatic objectives and the quartz 

 oculars. Table IV gives the magnifications which result from various optical com- 

 binations and optical camera lengths. The optical camera length is the distance in 

 centimeters from the top of the ocular to the plane of the photographic plate. 



Table IV. — Magnifications and Optical Camera Length for the Monochromats 

 AND THE Quartz Eyepieces at 160-mm. Tube Length and X = 275 m/x 



Mounted on the rear of the spark-generating stand is a mercury-vapor lamp in a 

 suitable metal housing. A flask in front of an opening in the housing contains a green- 

 filter solution. The flask and the filter solution concentrate the light of the mercury- 

 vapor lamp on a small mirror which may be swung against the prism face and thus 

 reflect the light into the microscope for preliminary adjustment and focus of the 

 microscope. 



Operation of Apparatus. — The objectives are provided with centering mounts 

 which first of all should be carefully adjusted so that, when the illumination is centered 

 for one objective, it will be practically centered for all objectives. The centering of 

 the objectives maintains the same field of view when objectives are changed. 



