Rapid Rectilinear Lens

A lens having a fairly large working aperture and free from distortion, having been corrected for spherical aberration, thus giving straight lines; i. e., the lines of buildings or similar objects are correctly reproduced, not distorted. (See Lens, Rectilinear.)

Rapid Symmetrical Lens

A rapid rectilinear lens, the two combinations of which are of the same focal length and of identical construction.

Rectigraph Lens

A synonymous term for the rectilinear lens.

Rectilinear Lens

A lens in which straight lines are rendered perfectly on the sensitive plate; i. e., straight lines are not curved or distorted. A rectilinear lens works with a fairly large aperture, and for all around work, where speed is not the essential requirement, the rectilinear type of lens is of great value.

Single Lens

A lens in its simplest form, usually constructed of only one piece of glass. If the lens is achromatic it may be made of two or more glasses cemented together. These glasses have different refractive and dispersive power. Single lenses will not give straight lines, and, therefore, are not available for architectural work. Their chief use is for landscape work. In the majority of cases it is necessary to use a very small aperture in order to cut out the marginal rays of light which would give a distorted image.

Sizes of Lens

Quarter size

for 3 1/4 x 4 1/4 plates.

Half size

for 4 3/4 x 6 1/2 plates.

Whole plate, or 4-4 - for 6 1/2 x8 1/2.

Other lenses expressed by inches, according to the plate they are made to cover.

Stigmatic Lens

A lens free from astigmatism; also corrected for chromatic and spherical aberration. Gives an image having a perfectly flat field when worked even with a large aperture.

Supplementary Lens

Single lenses made for various purposes to slip over (similar to a cap) the ordinary lens. They either shorten or lengthen the focus of the ordinary lens.

Symmetrical Lens

A rapid rectilinear lens, the two combinations of which are of identical construction, and when used separately have a focal length almost double that of the combined lens.

Telephoto Lens

An attachment consisting of a tube and a negative lens, which is used in conjunction with the positive lens for photographing objects situated at considerable distance from the camera. A telephoto lens magnifies objects in the same manner as a telescope.

Tessar Lens

The name given to a highly corrected anastigmat lens which works at a large aperture, originated by Zeiss. Manufactured in the United States by Bausch & Lomb.

Lens Tests

The majority of lenses of reputable make are practically free from defects at least they may be relied upon so far as guaranteed or described by the manufacturer. The following tests will, however, prove of value, should one desire to ascertain the value of a lens or to test it while having it on a few day's trial: