An introduction to the science & practice of photography (1891)
Jones, H. Chapman (Henry Chapman), 1854- · London : Iliffe & Son · leaf 137
he spherical aberration. Lenses of the type illustrated in figure 19 may have their apertures enlarged to |, but with this aperture the definition is no- where sharp, though sharp enough for large portraits. Other portrait lenses than those already mentioned have been introduced from time to time… … Fig. 33. Voigtlander made lenses in which the ordinary back com- bination of the Petzval lens was replaced by a cemented combination so constructed that both combinations had outside surfaces of equal curvature. Each combination was of the same focal length, which was two-thirds of the focal length…
Photography
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