Ramsden Eyepiece is a positive eyepiece, Fig. 40, 

 and is constructed of two plane convex lenses with the 

 convex surfaces toward each other. It is especially 

 useful as a micrometer eyepiece in microscopes and 

 telescopes, as it is used as a magnifier on the fine 

 divisions of the micrometer and at the same time gives 

 the virtual image. 



Fig. 44. 



Periscopic, Orthoscopic arid Kellner Eye- 

 pieces are also positive eyepieces which are achro- 

 matized by having the eye lens a doublet or triplet. 

 The spherical correction is such as to produce a large 

 and flat field, Fig. 44. 



Projection Eyepiece. This is constructed to 

 throw an enlarged image on a screen at a distance 

 from the instrument and for photographing the image. 



109 



