The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Conjugate Foci                                               Contact, Optical
diverge, and are condensed by the large lens beyond d. The best form when only two lenses are used, is that shown in fig. 36, according to Mr. Traill Taylor, whose notes on this subject we have condensed, and consists of a plano-convex lens with its flat side
Fig- 35-
to the radiant, the second lens being a crossed lens. Most con-densers are made of crown glass, and have a slightly greenish tinge. Colourless optical flint would be better, but the price would be higher. All condensers should be so loosely mounted
Fig. 36.
in thin cells that they can be turned round, otherwise the expan-sion by the heat may cause them to crack. Clock glasses filled with liquid have been suggested as condensers for enlarging, but are so long in focus as to be practically useless.
Conjugate Foci. See Focus.
Constants, Table of. See Calculations and Constants.
Contact, Optical. Any two substances brought into close union one with the other, so as to absolutely join, and made to present but two instead of four surfaces, are said to be in optical contact. A familiar example is the common mirror, where the amalgam and glass are in optical contact.