Back Combination Lens

The portion of a doublet lens located nearest the ground-glass. In most cases, when used without the front combination, it has a focal length almost double that of the complete lens combination and will produce an image practically double the size of that obtained by the complete lens.

Biconcave Lens

Double-Concave, Concaval-Concave. A term applied to a lens thinner in the center than at the margin and having both sides hollowed out.

Biconvex Lens

Double-Convex, Convexo-Convex. A term applied to a lens thicker in the center than at the margins, and having both sides extending outward in the form of a sphere.

Celor Lens

A highly corrected anastigmat lens, having a large aperture. Manufactured by Goerz.

Collinear Lens

An anastigmat lens having large aperture and great covering powers. Manufactured by Voigtlander.

Concave Lens

A lens hollowed or depressed in the center.

Concave, Double Lens

Biconcave or Concaval-Concave. A lens in which both sides are hollow or concave.

Concave, Piano Lens

A lens having one side hollowed out, the other being plane or flat.

Concavo-Convex Lens

A lens hollow on one side, the other being raised or convex.

Convergent Lens

A lens which will bring the rays of light to meet in a focus a convex lens

Convertible Lens

A lens in which the various combinations may be arranged differently, or used separately, thus giving different focal lengths.

Convex Lens

A lens the surface of which is in the shape of a sphere, the center being thicker than the margin.

Convexo-Concave Lens

A lens convex on one side and concave on the other.

Convex, Double Lens

A lens which is convex on both sides.

Convex, Piano Lens

A lens convex on one side and plane on the other.

Cooke Lens

An anastigmat lens constructed of two lens combinations and a third single lens. Manufactured by Taylor, Taylor & Hobson.

Covering Power of Lens

A term which signifies the field or area of illumination of a lens; i. e., practically speaking, the size of a plate a lens will cover, or on which a well-defined image will be reproduced.

Dagor Lens

A highly corrected anastigmat lens. Manufactured by Goerz.

Dallmeyer Lens

One of the first types of portrait lenses, and still a favorite with many portrait photographers. Manufactured by Dallmeyer.

Doublet Lens

A lens composed of two separate combinations.

Dynar Lens

The name applied to a highly corrected anastigmat lens. Manufactured by Voigtlander.

Euryscope Lens

A rectilinear lens having a large aperture. Used for portraiture as well as for landscape work. Manufactured by Voigtlander.

Field of Lens

The illuminated space on a screen made by a lens working with full aperture. If the corners of a negative are transparent, the field of the lens is not large enough for that particular size of plate.