ELEMENTARY PHOTO-MICROGRAPHY. 



33 



phragm, taking care that the lighting of the ground- 

 glass screen is both uniform and sufficient to ensure 

 a background of tolerable density. Oblique light, 

 although very good for visual inspection, is ill 

 adapted for photography, and without great care 

 will result in a blank negative, even after long 

 exposure. 



The writer has never found the Lieberkuhn of 

 any advantage in illuminating opaque objects. A 

 reflector called a vertical illuminator may be tried 

 when the lens approaches so near to the object that 

 it is difficult to project a beam of light from the side 

 reflector. It is especially useful for photographing 

 metals with high powers or objects mounted dry on 

 cover. 



Fig. ii. Arrangement of the side reflector for opaque objects. 



