THE DEVELOPMENT OF THE PHOTOGRAPHIC OBJECTIVE 



47 



small Galilean telescopes with the eyepiece racked out far enough to project a real 

 image on the photographic plate. By 1891, optical manufacturers began making 

 achromatic negative lenses in adaptors by which they could be mounted behind ordi- 

 nary photographic lenses. Such "telenegative" lenses were rather unsuccessful on 



Fig. 52. 



-Busch Bistelar, 2 X, 



f/7. 



Fig. 53.— Zeiss Magnar 3 X, //lO. 



account of the low speed and poor correction of the whole system, but at// 11 or less 

 they could be useful. By varying the separation of the telenegative lens from the 

 positive lens, the over-all power of the system could be changed, such adjustable or 

 Pancratic lenses giving a range of from 2 X to 8 X magnification. 



I _ 



Fig. 54. — Dallmeyer Dallon //5.6. 



Fig. 



55.— Taylor-Hobson 2 X, 

 //3.5 telephoto lens. 



However, it was soon realized that even a magnification 2 X is a very considerable 

 advantage, and in 1898 Zeiss produced a complete telephoto lens of 2 X to 3 X power, 

 at an aperture of //6 to// 10. This was followed by other fixed-focus telephoto lenses, 

 notably the Busch Bistelar 2X f/7 (Fig. 52) designed by Martin in 1906, and the 



Fig. 



56.— Taylor-Hobson 2.3 X, //5 

 distortionless telephoto. 



Fig. 57. — Zeiss Tele-Tessar. 



Zeiss Magnar 3X (Fig. 53) //lO by Rudolph and Wandersleb. Both these systems 

 consisted of a cemented positive doublet in front and a cemented rear negative doublet. 

 Most manufacturers have made telephoto types since 1900, of various constructions. 



Fig. 



58. — Voigtlander Tele- 

 Dynar, //6.3 lens. 



59. — Voigtlander Tele- 

 Dynar //4.5 lens. 



but the aperture remained low until the Dallmeyer Dallon //5. 6 lens (Fig. 54) designed 

 by Booth in 1919, and the Taylor-Hobson 2 X telephoto //3. 5 by Lee in 1925 (Fig. 55). 

 The inevitable distortion of ordinary telephoto systems was finally overcome by Lee 

 in the Taylor-Hobson distortionless telephoto //5, 2.3 X (Fig. 56). 



