An introduction to the science & practice of photography (1888)
Jones, Chapman · London : Iliffe & Son · leaf 140
and as with a doublet this distance is considerably less than the equivalent focal length, a given limit of camera extension may leave a margin with the latter lens, but be an inch or two too small for the former, though the focal lengths of both lenses are the same. In those cases where the… … Fig. 39. in the same way as before, as shown in fig. 39. Here a b and c d represent rays passing through the optical centre, and the dotted lines indicate the point of admission or emission that is not identical with the optical centre. The optical centre of a symmetrical doublet is its mechanical…
Photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
