208 



PHO TO-MICROGRAPHY 



[CH. VIII 



Fig. 170. Turner-Reich 

 anastigmat objective for pho- 

 tography, ( Gundlach Opt. 

 Co.) 



In the camera here fig- 

 ured, the camera bed is ruled 

 in centimeters so that the 

 position of the ground glass 

 can be determined with ac- 

 curacy and noted. It takes 

 but a moment to set the 

 ground glass or focusing 

 screen at the right level to 

 give any desired size. In 

 practice it is convenient to 

 have attached to the camera 

 a table giving the position of 

 the ground glass for various 

 sizes, and also the distance of 

 the objective from the object 

 in each case. By having this 

 information it takes but a 

 moment to set the camera 

 and to place it so that it 

 will be approximately i n 



Fig. 170. 



Fig. 171. Zeiss anastigmat objective 



for photography, (Bausch & Lomb Opti- 

 cal Co. ) 



focus. The final focusing is then accom- 

 plished by the use of the rack and pinion 

 movement. It is an advantage to use a 

 focusing glass and a clear focusing screen 

 or the transparent part of the ordinary 

 screen (Fig. 174), for the final focusing. 

 As many objects have not sharp details 

 which one can focus on, it is helpful to 



place some printed letters on the part to be brought out with the greatest sharp- 

 ness. Of course these are removed before the exposure is made. , 



\ 339. In lighting the object one should take pains to so arrange it with ref- 

 erence to the light that the details will show with the greatest clearness. Naturally 

 for the vertical camera the light will come from the side and not from a skylight, 

 although good results are obtained with a skylight if one so places the camera that 

 it does not cast objectionable shadows. 



Fig. 171. 



