48 



HANDBOOK OF PHOTOGRAPHY 



Other types of telephoto lens are the Zeiss Tele-Tessar (Fig. 57) ; the Voigtlander 

 Tele-Dynar (Figs. 58, 59); the Ross Teleros (Fig. 60) and Telecentric (Fig. 61); the 

 Stable Neoplast (Fig. 62); the Plaubel Tele-Makinar (Fig. 63); the Schneider Tele- 

 Xenar (Fig. 64); and the Goerz Telegor (Fig. 65). 



The telephoto lens is now enjoying a new lease of life with the advent of miniature 

 cameras and amateur motion pictures on 16-mm. film. It should be pointed out, 



Fig. 60.— Ross Teleros. 



-Ross Telecentric. 



however, that for these purposes some firms sell ordinary lenses of relative^ long 

 focus under the name of telephoto lenses, which are designed to give larger pictures 

 than are obtained with the standard lens for that type of camera. This practice is 

 justified by the much better definition and larger aperture obtainable with ordinary 

 lenses than with real telephoto lenses. 



Reversed Telephoto Systevis. — In some cases, particularly with very short-focus 

 lenses, the working distance (or back focus) is too short to accommodate auxiliary 



I 



Fig. 62. — Stable Neoplast. 



Fig. 63.— Plaubel 

 Tele-Makinar. 



apparatus such as the mirror in a reflex camera, the shutter in a cine camera, and in 

 particular the beam-splitting prism of a Technicolor camera. In such cases there is a 

 real advantage in placing a negative lens in front and a positive lens behind. 



A notable example of this general construction is the Hill lens made by Beck 

 (Fig. 66) to photograph the whole sky in a single picture. 



Fig. 



-Schneider Tele-Xenar. Fig. 65. — Goerz Telegor. 



Fig. 66.— Hill 

 sky lens made by 

 Beck. 



Process Lenses. — ^Lenses for making half-tone and other printing blocks are 

 designated "process lenses" and usuallj^ operate at approximately unit magnification 

 and at low aperture (say //lO to //30). For these reasons a symmetrical type of 

 construction is generally adopted, favorite types being the Celor or Homocentric 

 forms containing four separated single lenses. Actually for photographing black 

 lines on a white ground, the stray light due to internal reflection between eight glass- 

 air surfaces is liable to cause loss of contrast, and it is likely that clearer reproduction 

 might be obtained if a lens having fewer glass-air surfaces such as the Dagor were used. 



