The Dictionary Of Photography

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

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Lunar Caustic
than to use the commercial paint; and a similar mixture thinly spread on paper makes a good phosphorescent screen for use in experiments on Radiography {q.v.).
Lunar Caustic. See Silver Nitrate.
Luxograph. A large lantern-like device with tissue paper front in which pyrotechnic or other compounds can be burned to give an artificial light for portraiture. (See Portraiture and Flash Light.)
Macro-Photography. A term used to denote the enlarge-ment of the negative.
Magic-Lantern, or Optical Lantern. An apparatus used to project a magnified image of a positive upon a white screen in a darkened room. Practically it consists of a tin box, in which is placed a lamp in the focus of a silvered reflector, the light being condensed by a pair of plano-convex lenses, the positive being placed close to the condensers, and a special photographic lens being placed at the focus of the condensing lens. Very often a three- or four-wick lamp is employed to give the illumination, the edges of the flames being presented to the condensers; but limelight, acetylene, and the electric arc are also in use. The following rules and table will be found useful in determining the dimensions of the pictures thrown on the screen with various lenses : -
i. Knowing the length of room and diameter of picture desired, required to find the focus of front objective of lantern. Multiply the distance between the lantern and screen by the size of the opening in slide, and divide by the diameter of disc.
Example. Room length 50 feet, diameter of picture 20 feet; required to know focus of lens to be used. (Three inches is always taken as the size of opening of slide.)
2. Having a given focus lens, and given diameter of picture, required to know what distance from screen to place lantern. Multiply the diameter of picture required by the focus of the lens, and divide by the diameter of the slide.