1 30 PHOTOMICROGRAPHY 



to draw forward and away from the camera back, and the 

 image then focussed on a piece of paper or card placed 

 over the ground glass, or a rack focussing movement 

 may be fitted to the camera back, or better still to the 

 object-holder. 



In the Leitz apparatus arranged for the photography 

 of insects, and shown at Fig. 41, these details are well 

 carried out. The camera slides on tubes in such a way 

 that the front and back can both be moved to get a 

 rough adjustment, and be clamped in any desired 

 position. The object-carrier has a screw motion for 

 final focussing, and is worked by means of a rod from the 

 camera back. A shutter actuated by a bulb is carried 

 on the camera front, to which a conical adapter is 

 attached to bring the small lenses well forward between 

 the lamps. 



A vertical camera is sometimes more convenient 

 than a horizontal, particularly when dissections or small 

 preparations in water or spirit have to be photographed. 

 Many of the vertical cameras are very portable, and can 

 be carried into the position where the best light is obtained. 

 Diffused daylight is generally all that is necessary, 

 requiring exposures of a few seconds with ordinary plates, 

 up to about five minutes for autochromes. Fig. 42 

 illustrates a vertical arrangement, and includes a 

 bull's-eye for projecting a beam of light on to the object. 



Lenses. The lens is the most important part of the 

 equipment. Rapid rectilinear photographic lenses of 

 good make are fairly satisfactory, but the superiority 

 of an anastigmat is very marked. It must be of short 

 focal length, otherwise an impossible bellows extension 

 is required for even small magnifications, and lenses of 

 4" to 5" focus, such as are fitted to quarter-plate cameras, 

 are about the largest that can be conveniently used . The 

 small anastigmat lenses specially designed for photo- 

 micrography are the most suitable. A magnification of 8 



