14 



* Projection Eye-pieces. 



The Projection eye-pieces introduced by us simultaneously with the compen- 

 sating eye-pieces, both of which arc corrected on the same principle, are designed 

 exclusively for the purposes of micro-photography and micro-projection. 



For detailed information as to their construction and special application 

 we would refer to tJic new edition of our Catalogue of Photo-micrographic and 

 Projection Apparatus. 



The prices of the various forms of Projection Eye-pieces will 

 be found in the Price-list at the end of the Catalogue. 



Aided by the considerably extended list of materials produced by the local 

 glass works we have reconstructed most of the older types of our achromatic 

 objectives so as to obviate in these lenses also, more completely than had 

 formerly been possible, imperfections due to spherical and chromatic 

 aberration. With those lenses of the dry series which have a numerical 

 aperture exceeding 0.65 this improvement, apart from greater sharpness and 

 clearness of the image, is also manifested by increased sensibility to 

 differences in the thickness of the cover-glass and the length of tube. 

 Consequently, in the use of these lenses now even closer attention must be given 

 to these two points than formerly. 



Fig 1 . 5. Objectives ai, a2, as, 



attached to the tube. 



(7 2 Full Size.) 



Fiff. 6. Objectiv a*. 



By rotation of the ring RR the 

 upper pair of lenses (Z 2 ) may be 

 elevated into the position Z',, in- 

 dicated by dotted lines. 

 (Full Size.) 



