260 



PROJECTION MICROSCOPE 



[ CH. IX 



three kept on the nose-piece most constantly a 64, 42 and 6 mm is as 

 good a combination as one can get. Other powers should be available, 

 however, and for special specimens and occasions one may employ the 

 two mm. oil immersion. For powers above 20 mm., ordinary objectives 

 are more satisfactory than most projection objectives. 



S 41S. Projection Oculars (Fig. 185). — If one uses the apoch- 

 romatic objectives of 16 and S mm. focus the projection oculars are 

 used with them. They can also be used with wide angle achromatic 

 objectives. With them one can get an enormous magnification even 

 with the 16 mm. objective. (See the table below, § 421.) 



These oculars restrict the field greatly and in the writer's exper- 

 ience it seemed on the whole more desirable for most objects not to use 

 the projoction oculars. They cannot be used advantageously with 

 objectives higher than S or 6 mm. and are most satisfactory with one 

 of 16 mm. 



In using the projection ocular with a 16 mm. objective one can 

 place the special achromatic condenser next the stage, but if the ocular 

 is not used one must either do without a specimen condenser, or take 

 one of lontrer focus, if he has two or three as shown in Fis;. 207. 



lililllllllllllL,, , 



Fig. 211. 



Fig. an. Zeiss' Micro-Planar for projection. (Cut 

 loaned by Bausch <Sf Lomb Optical Co. ) 



T/ie micro-planars are of 20, 35, 50, 75, and 100 mm. 



equivalent focus. When used for projection the special iris 

 in each should be wide open. These are used -without a 

 projection ocular. 



Fig. 212 A. Fig. 212 B. 



Fig. 212. Leitz objectives of 64 (A), and 42, mm. B). For micro-projection. 



(Cut loaned by II "in. Krafft, N. )'.) 



These arc used without a projection ocular. The iris in the 64 nun. objective 

 should be -wide open for micro-projection . 



§419. Arrangement of the Parts of the Projection Micro- 

 scope. — As stated in section 399, all the parts of the apparatus should 



