Eyepieces. 



49 



9 - Projection 

 Eyepiece. 



Projection Eyepieces. 



These were designed specially for pro- 

 jecting objects on to the screen and for 

 photographic purposes. They give an 

 exceedingly small field, but an exquisitely 

 sharp one. There is provision for moving 

 the position of the eye-lens in these, and 

 in order to get good results with them 

 it is necessary to do this until the stop 

 between the lenses is sharply projected 

 on the screen. All photo-micrographers 

 of note use these eyepieces, but as 

 they have the same corrections as the 



compensating eyepieces, they cannot be 



, . , , , . 



employed with low power ordinary 



achromatic objectives. With the higher powers, however, 

 from, say, ^-iiich of N.A. '80, they work well. For 

 photographing with ordinary objectives of low power, the 

 ' A ' eyepiece gives good results. 



Binocular Eyepieces. 



As we have mentioned under ' Binocular Microscopes/ 

 most of the Continental firms do not make the binocular 

 microscope. Therefore, for those who desire to be able to 

 employ both eyes, they make a binocular eyepiece, but only 

 for the Continental length of tube, and this should be 

 particularly understood. The one with which we are 

 acquainted is that designed by Abbe, and manufactured by 

 Zeiss, as figured page 50 (Fig. 10). It gives stereoscopic 

 effects and most beautiful results with both high and low 

 powers. It is somewhat expensive, which necessarily 

 restricts the sale, and is therefore a luxury ; although 

 perhaps desirable, it is not necessary. 



There is no universally adopted size of fitting for eye- 

 pieces, consequently every maker, has his own gauges, 



