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 177
Fig. 28a. The focal length of the lens was 13 inches and the book was moved away so as to make the central width about as in Fig. 28. Fig. 28b. The telephoto lens had about 30 inches equivalent focal length.
Photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
