C. A. Steinheil S6hne, Miinchen. 



109 



Aplanatic Focussing Lenses. 



Aplanatic combination consisting of three cemented lenses, with 

 large flat field free from distortion and achromatized for intra and 

 extra-axial rays. (For further particulars vid. M. Schultze's paper in 

 Schultze's Arch. f. Mikr. Anat. Vol. II, 1866.) 



Tele -photographic Objectives, 

 .T 



consisting of an ordinary photographic objective (of not less than ra- 

 pidity f/7) and a magnifier achromatized for chemical and visual rays. 

 (vid. Photogr. Corresp.; Vienna, Leipzic, 1892, June and November, pp. 308 and 546). 



The magnifier is a triple system of negative focus. The combination of 

 the triple system with the photographic objective of positive focus increases the 

 equivalent focal length of the total telescope objective. This equivalent focal 

 length and thus also the magnitude of the image are made to vary according 

 to the distance between objective and concave lens, which is fitted with rack 

 and pinion, the distance between the object and the objective being constant 

 during these variations. 



The field of the combination measures about 10. The magnification may 

 at the expense of brightness be increased to 10 or 15, only a relatively small 

 extension of the camera being required to produce these magnifications ; the latter 

 is owing to the principal point of the combination being placed a long distance 

 in front of the latter. 



The time of exposure amounts under favourable circumstances only to 

 fractions of a second, but even instantaneous exposures may be made. 



The instantaneous photographic telescope , 



which was first made for the German navy in 1890, appears, owing to its 

 brightness, to be specially adapted to this purpose, (vid. Dr. Ad. Steinheil's 

 paper on ,,Tele-photography" ', Phot. Corresp. Vienna, Feb. 1892). The optical 

 part consists of a double objective and a negative elongation lens, having a 

 total equivalent focus of 1.3 meter. 



