Fig. 1. — Meniscus 

 landscape lens of Wol- 

 laston. 



Fig. 2. — Achro- 

 matic landscape lens 

 of Chevalier. 



CHAPTER III 



THE DEVELOPMENT OF THE PHOTOGRAPHIC OBJECTIVE 



By R. Kingslake 



Landscape Lenses. — Historically, photographic lenses fall into two groups, the 

 early period prior to 1886 "and the anastigmat period since that time. In that year a 

 revolution occurred in lens design as a result of the successful development of barium 

 crown glass by Abbe and Schott, in Jena. 



The earliest photographs were made by placing paper covered with a light- 

 sensitive material in the focal plane of a camera obscura, the lenses used being first 

 simple plano-convex lenses, and later sim- 

 ple meniscus "landscape" lenses as sug- 

 gested by WoUaston in 1812 (Fig. 1). A 

 suitably designed meniscus lens, with a 

 stop in front of it on the concave side of 

 the lens, will give good pictures at //ll or 

 //16, covering with moderate definition a 

 total field of about 45°. This lens is still 

 universally adopted in low-priced cameras. 

 In addition to its cheapness, this lens has the advantage of possessing only two glass- 

 air surfaces. 



The lack of achromatism of this lens was soon found to be a disadvantage, even 

 before the camera obscura became a photographic camera, and the achromatic land- 

 scape lens was introduced by Chevalier in 1821 (Fig. 2). The process of achromatiza- 

 tion automatically removed both of the chromatic aberrations, thus improving the 

 definition in a twofold manner. 



The Petzval Portrait Lens. — The landscape lens at//ll was successfully adopted in 

 the early daguerreotype process, but exposures of half an hour or more were necessary 

 even in sunlight. Consequently when daguerreotype portraiture was attempted, the 



need soon arose for a much faster lens. J. Petzval, 

 of Vienna, solved the problem in 1841 by the design 

 of his well-known portrait lens (Fig. 3), which is 

 still popular although its regular manufacture has 

 been abandoned in recent years since the introduc- 

 tion of anastigmats of equal or greater speed. The 

 Petzval lens contained four single lenses and six 

 glass-air surfaces and covered a field of 25° at an 

 aperture of //3.4. This general design was subsequently improved by Dallmeyer, 

 Voigtlander, Zincke-Sommer, and Steinheil, reaching finally an aperture of //2.4. It 

 suffered from the disadvantage of astigmatic defects in the outer part of the field, 

 which could not be removed so long as the designer was limited to the use of ordinary 

 crown and flint glasses. 



Orthoscopic Lenses. — The processes of photography were at this time undergoing 

 rapid improvement, and by 1858 the wet-collodion process had become generally 

 adopted. Its relatively high speed made indoor and architectural photography a 



37 



Fig. 3. — Petzval portrait lens. 



