46 



HANDBOOK OF PHOTOGRAPHY 



lens with the rear half of the original Protar lens. The Tessar lens has been made in 

 apertures ranging from //15 as an apochromatic process lens, down to f/2.7 for cine 

 purposes. The field runs from 45 to 75°, depending on the aperture and focal length. 

 Modifications of the Tessar Type. — The first modification of the Tessar type of 

 construction was the Voigtlander Heliar //4.5 (Fig. 45) and Dynar //6 (Fig. 46) 

 designed by Harting in 1902, in which both the front and rear positive elements are 

 made into cemented doublets. In a sense, these lenses are thus modifications of the 



Fig. 44. — -Tessar lens 

 designed by Rudolph. 



Fig. 45. — Early model of 

 Voigtlander Heliar lens. 



Fig. 



46. — Voigtlander 

 Dynar. 



Cooke type. The Dallmeyer Pentac//2.9, designed by Booth in 1919, is of the same 

 general type as the Dynar. The modern Heliar lens is also of the Dynar type, the 

 original Heliar type being no longer made. In 1903, Harting designed the Oxyn 

 //9 (Fig. 47) for process work, in which the front element of a Heliar was combined 

 Muth the rear of a Dynar. This lens also is no longer made. In the Voigtlander 

 Heliostigmat (Fig. 48), the front lens is doubled but the rear lens is a single positive 

 element. This is a kind of inverted Tessar type. 



Fig. 47. — Oxyn lens 

 signed by Harting. 



Fig. 48. — Voigtlander 

 Heliostigmat. 



The Zeiss Biotessar //2.7 (Fig. 49), designed by Merte in 1925, is really a Dynar in 

 which an additional thin positive lens has been cemented to the front face of the rear 

 doublet making it into a triplet. 



Another modification of the Tessar is the Ross Xpres (1913) in which the rear 

 lens is a triplet instead of a doublet (Fig. 50). This is made in apertures from //1. 9 

 to//4.5, and covers a field of about 53°. The Gundlach Radar (Fig. 51) has also a 

 triplet rear element. 



Fig. 49. — Zeiss Biotessar 



f/2.7. 



Ross Xpres. 



Fig. 51. — Gundlach 

 Radar. 



Telephoto Lenses. — A telephoto lens consists merely of a pair of widely spaced 

 positive and negative elements. In such a system, the principal points are shifted out 

 beyond the positive element so that, if this positive lens is turned toward the object, 

 the true or equivalent focal length of the system Avill be much greater than the back 

 focus. Hence a lens of long focal length, giving a large image, can be used on a small 

 camera having a short bellows extension. The earliest telephoto lenses were merely 



