THE DEVELOPMENT OF THE PHOTOGRAPHIC OBJECTIVE 



45 



raised the aperture to //3.6 with a 65° field in his symmetrical Planar lens (Fig. 37) 

 by making both negatives into hyperchromatic negative doublets. This Planar type 

 has provided the inspiration for a number of recent unsymmetrical lenses of extremely 

 large aperture such as the Taylor-Hobson Opic //2 (Fig. 38), the Zeiss Biotar //1. 4 



Fig. 



-Wray Lustrar 



-Goerz Alethar process 

 lens. 



Fig. 37. — Ru- 

 dolph's symmetrical 

 Planar lens. 



(Fig. 39), the Schneider Xenon //2, the Bausch and Lomb Raytar //2.3, and the 

 Kodak Ektar J/2. In extreme cases the rear positive lens is also doubled, either 

 cemented or separated, as in the Xenon //1. 3. The Portrait Euryplan (Fig. 40) is 

 really of the Planar type. 



Fig. 38. — Taylor-Hobson 

 Opic //2. 



Fig. 



39. — Zeiss Biotar, 

 //1. 4. 



Fig. 



40. — ^Schulze Portrait 

 Euryplan. 



The Ernostar lens //1. 8 (Fig. 41) designed in 1924 by Bertele is a four-piece lens 

 in which the second negative has been made into a thick cemented triplet. The Meyer 

 Primoplan //1. 9 is similar, but the second lens is a doublet of deep meniscus form 

 (Fig. 42). In the Taylor-Hobson Super-speed Panchro //1. 3, the second lens is a 

 doublet and the rear a triplet (Fig. 43). 



Fig. 41.— Ernostar //1.8 

 lens designed by Bertele. 



Fig. 42. — Meyer Pri- 

 moplan //1. 9. 



Fig. 43.— Taylor-Hob- 

 son Super-speed Panchro, 

 //I.3. 



The Tessar Lens. — By cementing together the rear elements of an unsymmetrical 

 Celor-type lens, Rudolph in 1902 produced the Tessar lens (Fig. 44), which is probably 

 the best known and most generally used type of lens produced in recent times. 

 The glasses are the familiar dense barium crown for the positives and light fhnt for the 

 negatives, and the airspaces are adjusted to fulfill the Petzval sum. In a sense, the 

 Tessar can be regarded as an extension of the Cooke three-lens type, but it is, perhaps, 

 more accurate to regard it as a logical simplification of the four-lens type of construc- 

 tion. Another view is that the Tessar is a combination of the front half of a Cooke 



