METHODS OF STUDY 27 



tory were described (Contrib. Cushman Lab. Foram. Res., vol. 

 2, pt. 1, 1926, pp. 1-3) , and are repeated here. 



Various methods have been tried out for a number of years, 

 but always difficulty was encountered in getting sufficient depth 

 of focus with the desired magnification. Several years ago a 

 method was worked out by the writer, and later put into definite 

 form. It has continued to give excellent results. The main 

 idea has been to obtain a negative of the greatest possible depth 

 of focus regardless of magnification, and then the enlargement 

 from this negative to the desired size. In this way the details 

 are kept with the deep focus. 



For the actual photographing a vertical camera is used. The 

 particular camera used in the laboratory is a type "H", Bausch 

 and Lomb, with the camera parts to take 5x7 plates. Kits 

 are used in the plate holders for smaller sizes. Any good com- 

 pound microscope may be used. For objective the Micro-Tessars 

 of Bausch and Lomb are used. The 32-millimeter equivalent 

 focus has been found to be of the greatest value although those 

 of greater focal length are excellent for large specimens. For 

 focusing, the diaphragm should be wide open or nearly so, but 

 for the actual exposure the stop should be cut down at least 

 to 11 of the scale, or even to 22 to get the greatest possible sharp- 

 ness and depth. An ocular may be used if desired, but much 

 the best results are obtained without it. With the type "H" 

 camera with the bellows extended to full length, there is a mag- 

 nification of the image on the plate to about 18 to 20 diameters. 

 This will give an excellent depth. By all means a focusing 

 glass of some form should be used, and every change of speci- 

 mens very carefully refocused. The entire result depends on 

 this point of very exact focus. With the combination of a 32- 

 millimeter, no ocular, and bellows full length all the specimens 

 in a circle of about 5 millimeters may be photographed at once. 



For the lighting, one of the regular Bausch and Lomb 

 illuminating outfits with a 6-volt, 108-watt lamp is used. This 

 is placed in the most advantageous position, and then screwed 

 to the table to form a permanent fixture with a table switch. 

 With the microscope and camera fixed, the only thing needed is 

 to get the slide in position. The light from this unit will be 

 found very intense and the shadows it casts very dark. In the 

 laboratory here a counter-light is used. This a 250-watt, 115- 



