Ch. VII] 



I'HOroCRAl'IlIXC with Tin: MK'KOSCOI'i: 



229 



A plan used by many skilled workers is to light the object and the 

 field around it well and then to place a metal diaphragm of the proper 

 size in the camera very close 

 to the plate holder. This will 

 insure a clean, sharp margin 

 to the picture. This metal dia- 

 phragm must be removed while 

 focusing the diaphragm of the 

 projection ocular, as the dia- 

 phragm opening is smaller than 

 the image of the ocular dia- 

 phragm. 



If the young photo-microg- 

 rapher will be careful to select 

 for his first trials objects of 

 which really good photo-mi- 



Exc 



Fig. 135. View of the Back 1 

 of the Objective, Showing the Con- 

 denses out of Center and Centered. 



Exc The spot of light (D) is to one 

 side of the center, showing that the optic 

 axis of the condenser is not in line with 

 that of the microscope. 



C The spot of light (D) is in the center, 

 showing that the optic axis of the con- 

 denser and microscope are in line. 



crographs have already been 



made, and then persists with each one until fairly good results are 



attained, his progress will be far more rapid than as if poor pictures 



of many different things were 

 made. He should, of course, 

 begin with low magnifications. 

 § 353. Adjusting the objec- 

 tive for cover-glass. — After 

 the object is properly lighted, 

 the objective, if adjustable, 

 must be corrected for the 

 thickness of cover. If one 

 knows the exact thickness of 

 the cover and the objective is 

 marked for different thick- 

 nesses, it is easy to get the 

 adjustment approximately cor- 

 rect mechanically; then the 



final corrections depend on the skill and judgmenl of the worker. 



It is to be noted too that if the objective is to be used without a 



Exc 



l r ii.!.)) of the Microscope 

 showing the Light in the Center and 

 to One Side. 



Fin. i*6. 



C Fl The light is in the center and 

 illuminates the object. 



Exc Fl The light is at one side of the 

 center and dues not illuminate the objeel . 

 (The field is not fully lighted, as a low 

 power is used to center the object and 

 the light). 



