166 THE USE OF THE MICROSCOPE 



3. If the objective focus is raised as in 2 (or the tube 

 length is increased), then the eyelens functions as a camera 

 lens, for which it was not calculated and is not particularly 

 suited. 



Methods for Optimum Photography. — The methods 

 which can yield optimum results in photographing with the 

 microscope are probably the following. 



1. Having focused the microscope (Jor distant vision), 

 clamp its tube in place, and center a small photographic 

 camera, focused for distance, close over the eyepiece. If 

 the camera lens is truly centered in the optic axis, the 

 pictures should be correct. The diaphragm of the camera 

 is not used, for the eyepiece circle of the microscope 

 functions as diaphragm. (Metzner.) 



2. Focus the microscope, and clamp the tube. Remove 

 the eyepiece, and insert a projection eyepiece. The 

 focusing on the camera screen may then be done by moving 

 the upper lens of the projection ocular, which is a specially 

 corrected photographic triplet. Thus the screen may be at 

 any distance. Or the diaphragm of the projection ocular 

 may be first focused on the screen, and the image then 

 focused by the micrometer screw of the microscope. 



3. Instead of the usual eyepiece, a strongly concave 

 corrected lens (homal) is used; the tube being shortened 

 by 20 millimeters. The photographic plate is put at 

 (or near) the correct distance, determined by focusing 

 the object previously with an ordinary eyepiece and clamp- 

 ing the tube ; or fixed, once for all, in a special small camera 

 (Phoku of Zeiss). 



The projection eyepiece is used with the objective at its 

 right tube length, and at its right working distance. 

 But it does not give a quite flat field, which is necessary for 

 photographs of blood films, and similar preparations. 

 Such a flat field is given by the homals (40), a series of 

 strongly negative compound lenses, which throw a magni- 

 fied image (with a magnification of about 5 times) on 

 a photographic plate at a given optimum distance. Sieden- 

 topf's photographic attachment screws on to the body 



