The Dictionary Of Photography

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

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Paper Negatives
Paper Negatives. The first negatives made by Talbot were on a basis of paper, and were made sufficiently transparent by waxing. Any of the more sensitive development papers may be used in the camera for negative making.
Papyrotype, Papyrography, or Papyrotint. Methods of photo-lithography, in which paper is used as the material on which the original transfer is made.
Parabola is the curve described by a moving point, which is always at the same distance from a fixed line, its directrix, that it is from a fixed point, its focus. -The chief use in photography of the parabola is in the construction of mirrors or reflectors for artificial light, their value being based on the fact that the rays of a luminous point in the focus of a parabolic mirror will be re-flected as a parallel bundle.
Parallax Stereogram. The parallax stereogram of Mr. Ives is a positive transparency which consists of narrow stripes alternately derived from the two halves of a stereogram ; and in front of this composite positive, but not quite in contact, there is fixed a line screen which is adjusted that each eye sees its appropriate set of stripes. Mr. Ives explains that this result is obtained by placing a line screen in front of the sensitive plate in the camera, slightly separated from it, and forming the image with a 3i-in. diameter lens, behind which are two small apertures places at the pupillary distance apart. The resulting photograph (a posi-tive from the original negative) is viewed through a similar screen, from approximately the same distance as the focal length of the lens. Each aperture of the lens forms an image made up of shaded lines, and, owing to difference of parallax, the lines constituting the two elements of the stereogram are separated and alternate with each other ; and for the same reason each eye picks up all of the lines belonging to the respective element of the stereogram, while the lines constituting the other element are hidden from that eye by the opaque lines of the covering screen.
Paramidophenol. See Amidol.
Paramidophenol Developer. See Development and Developers.
Paste. See Mountant.