C. A. Steinheil Sfihne, Miinchen. 113 



Astronomical and Physical Instruments. 



Achromatic Telescope Objectives 



of short focus, brightness f/4: composed of three cemented lenses, being 

 one crown glass lens placed between two flint glass lenses, in brass mount. 

 Achromatic Double Objectives, reversion of Fraunhofer's formula, 

 i. e. flint in front, brightness f/10 to f/ 18 free from distortion (vid. 

 Dr. Ad. Steinheil's paper in the ,,Sitzungsberichte der Munchener 

 Academic der Wissenschaften" , Vol. XIX, 1889, p. 413, entitled ,,Ueber den 

 Einfluss der Objectivconstructionen etc.") 



Astro -Photographic Objectives 



composed of two cemented lenses made of glass w T hich absorbs only a very 

 small portion of the chemical rays, corrected for the chemical part of the 

 spectrum regardless of the position of the visual image; field 2 to 3; 

 specially constructed for sideral and seleno-photography (vid. the papers 

 of Dr. Scheiner, assistant at the Potsdam observatory, in the ,,Zeitsclirift 

 fur Instrumentenkunde" , Oct. 1891, p. 374: , } Photographische Himmelskarte" 

 and also in the appendix of the ,,Abhandlungen der Konigl. Preuss. Academic 

 der Wissenschaften zu Berlin, 1892, Sitzungsberichte, Vol. XXXII, p. 583 etc.: 

 Tin large cluster in Hercules." 



Oculars. 



A. Astronomical Oculars. 



A D Mittenzwey Ocular; convexo-concave collective lens and 

 plano-convex eye lens; the image is formed between the lenses; field 

 about 50: free from reflections. 



Achromatic Micrometer Oculars. 



A F Double Ocular consisting of two achromatic objectives; 

 image before the lenses, apparent field about 40. 



A G Monocentric Micrometer Ocular, consisting of three 

 cemented lenses (2 flint glass menisci and a spherical lens) ; all radii 

 struck from the same center; completely free from all reflections: 

 apparent visual field about 36. 



A H Aplanatic Micrometer Ocular, also consisting of three 

 cemented lenses (1 biconvex crown lens placed between 2 flint menisci) 

 and, therefore, entirely obviating reflections; free from distortion, inter 

 and extra-axial achromatization. The image is perfectly flat and the 

 first surface is far removed from the plane of the image. For this 

 reason these oculars are specially suited for use in conjunction with 

 cross line micrometers; apparent field about 20. 



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