An introduction to the science & practice of photography (1888)
Jones, Chapman · London : Iliffe & Son · leaf 130
his " Euryscopes" working at in 1877, and his " Portrait Euryscopes" with an aperture of f, in 1886. At the same time that J. H. Dallmeyer obtained a patent for his wide angle rectilinear lens, 1866, he got pro- tection for a modification of the Petzval portrait lens, in which the flint component… … Fig. 31. that the back flint might be moved backwards to a certain and definite extent, thus introducing, when required, a definite and exactly reproducible amount of spherical aberration. This he called " diffusion of focus," a very good and perfectly descriptive term, although it has been much…
Photography
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