ELEMENTARY PHOTO-MICROGRAPHY. 69 



First throw back the ground-glass screen 

 leaving the end of camera perfectly open, then 

 place yourself in a position to look right through 

 both camera and microscope, with face about 

 i8in. away from open end of camera. Take an 

 ordinary hand reading glass of, say, gin. focus, 

 and hold it midway between the eye and the end 

 of camera, moving either the eye or the glass, or 

 both, until the glass is seen full of light with the 

 image of object in centre. After a few trials, not 

 only will the object be seen showing all the finest 

 details, such as would be shown if viewed through 

 the eyepiece on the tube of microscope in the 

 usual way, but the brilliant image enables one to 

 focus the most difficult test object. 



The ordinary focussing glass also may be used 

 at the open end of camera, in which case its 

 position would be the same as if it rested on the 

 glass, supposing the glass screen to be there. 



There are certain slides sold as test objects, and 

 if the photographer wishes to satisfy himself that 

 his objectives possess power of penetration, defini- 

 tion, flatness of field, and coincidence of visual 

 and actinic foci, he cannot do better than test the 

 value of his lenses by taking a photograph of 

 some well-known object suitable for the power 

 used. Any good book on the microscope will give 

 information on this point. Markings of diatoms, 

 the proboscis of the blowfly, the pygidium of the 



