Projection Eyepieces 81 



Kellner Eyepieces. 



This is an achromatic form of eyepiece, giving an ex- 

 ceedingly large field, which is considerably used for the 

 examination of animalculse, pond life, etc. A certain 

 amount of definition is, however, sacrificed in working with 

 it, and although occasionally of use, we should recom- 

 mend the microscopist, before purchasing any, to judge for 

 himself as to the desirability or otherwise of his having 

 them ; they are not by any means necessary adjuncts. 



Projection Eyepieces. 



These were designed specially for projecting objects on 

 a screen and for photographic purposes. They give an 

 exceedingly small field, but an exquisitely sharp one. In 

 order to obtain good results with these, it is necessary to 

 alter the position of the eye -lens until 

 the image of the diaphragm appears 

 sharply projected upon the screen. 

 For this purpose the eye-lens is mounted 

 in a tube having in it a spiral slot, 

 permitting of the eye-lens being moved 

 to and fro with great precision. They 

 are usually made in four powers, mag- 

 nifying 2 and 4 diameters respec- 

 tively for the short tube-length, and 3 

 and 6 diameters for the English tube- 

 length. The most serviceable are the 

 4 for the short tube and the 3 for the FIG. 22. PROJECTION 

 long tube. All photo-micrographers of EYEPIECE. 



note use these eyepieces, and they can usually be employed 

 to advantage, even with low -power achromatic objectives 

 of good quality. For photographing with ordinary objec- 

 tives of low power, the ' A ' eyepiece gives good results. 



Binocular Eyepieces. 



As mentioned under * Binocular Microscopes,' neither of 

 the leading Continental firms make the binocular micro- 



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