The science and practice of photography : an elementary textbook on the scientific theory and a laboratory manual (1920)
Roebuck, John R. (John Ransom), 1876-1965 · New York ; London : D. Appleton and company · leaf 198
PHOTOGRAPHY i68 will give the satisfactory definition with the larger stop will allow of the picture being taken in the least time, and is hence spoken of as the fastest lens. Lenses of different focal length may be com- … Fig. 43. Convertible Lens. pared if the size of the diaphragm is measured in terms of the focal length, that is in the P numbers. So that the speed of the lens is usually spoken of in terms of the largest stop it will allow for satis- Fig. 44. Petzval’s Portrait Lens. factory definition and be…
Photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
