A dictionary of photography for the amateur and professional photographer (1889)
Wall, E. J. (Edward John), 1860-1928 · New York : E. & H.T. Anthony · leaf 161
the superfluous powder is dusted off, the film is coated with collodion, and then well washed to remove the unacted-upon gum and bichromate ; the film may be detached from the plate, and used for enamels, ivory, opal, or any textile fabric. Principal Axis is the right line which joins the centres… … a a', the centres of curvature; aca% the principal axis; bb\ the secondary axis. A straight line passing through the optical centre, and making an angle with the principal axis, is termed a secondary axis. The centres of curvature are the points from which the arcs of the circles forming the…
Photography
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