Spherical Aberration

Securely fasten a sheet of newspaper to a perfectly flat surface, and then sharply focus the camera in the center. If upon examining the sides of the paper the letters are indistinct and blurred, the lens has not been corrected for spherical aberration.

Triple Convertible Lens

A lens in which the various combinations or cells may be used separately, thus giving different focal lengths. A triple convertible lens is one in which it is possible to have three different focal lengths. (See Lens, Unsymmetrical.)

Triplet Lens

A lens constructed of three separate combinations of glasses.

Unar Lens

An anastigmat portrait lens of high quality, originated by Zeiss. Manufactured in the United States by Bausch & Lomb.

Unsymmetrical Lens

A rectilinear lens in which the two combinations have different focal lengths. One of the single lenses will give an image about double that obtainable with both cells in combination, while the other cell will give an image 1/3 larger than the former cell.

Wide-Angle Lens

A lens embracing a wide angle of view. (See Angle of View.)


A small instrument used to determine whether the base of the camera is perfectly horizontal.

Chemical Action of Light

In photography, the blue and violet rays exercise the greatest chemical action, while the red and yellow rays have the least amount of chemical effect upon sensitive substances.

Continued Action of Light

In some printing processes the chemical action of the light continues even after the paper is printed and has been placed in the dark. This is the case in the carbon process.

Decomposition of Light

A ray of white light is decomposed on passing through a prism, i. e., separated into its constituent color rays.

Diffusion of Light

Light which is not direct or is spread out i. e., light in the shade of a building - is termed diffused light. Ground-glass on a skylight produces diffused light in a studio.

Pencil of Light

An optical term applied to rays of light converging or diverging from a point.

Ruby Light

A non-actinic source of light for illuminating the dark-room. When made of proper material this light can be used with safety for handling and developing all ordinary dry plates. But, trichromatic and panchromatic plates must be handled either in total darkness, or a specially prepared green safe light.

Lime Chloride

Ca(ClO)2 + CaCl2 + 2H2O. Bleaching Powder or Lime Chlorinated. Deliquescent white powder; unpleasant saline taste. Partly soluble in water. A bleaching and disinfecting agent. Used as a hypo eliminator; also in toning baths.

Lime Light

Light produced by a jet of combined oxygen and hydrogen gas, being thrown upon a cylinder of lime, producing a dazzling white light.

Linear Perspective

(See Perspective.)