ELEMENTARY PHOTO -MICROGRAPHY. 67 



ments and for moving the mechanical stage and 

 iris diaphragm, all of which may be easily reached. 

 The rough focussing should be done through the 

 eyepiece, with the camera and sliding block re- 

 moved, as explained previously. 



After the camera is replaced, a little time in 

 trying different effects will not be wasted, for 

 there is no possibility of getting a perfect picture 

 by a lucky shot, as sometimes happens when 

 using a hand camera. There is no place for chance 

 in photo-micrography, and a scientific worker 

 whose aim is to depict Nature just as it is would 

 scorn to " doctor " his negatives for the purpose 

 of pictorial effect. 



The effects of closing the iris diaphragm, or a 

 slight oblique light if fine markings are desired, 

 or plain ground-glass between the condenser and 

 the lamp if white diffraction lines are too con- 

 spicuous, may all be tried. Perhaps a coloured 

 glass may be better. Then when a suitable result 

 is obtained, one has to be very accurate with the 

 fine adjustment, for everything else goes for 

 nothing if correct focus be wanting. 



With very transparent objects contrast can 

 often be improved by lowering the condenser 

 instead of closing the iris diaphragm. 



A vertical camera is better for oil immersion 

 objectives, though there is no difficulty when using 



