Achromatic lens

achromatic lens
a lens corrected for black and white photography; specifically one that brings visual rays to the same focus.

Achromatic Lens An Achromatic lens is a system of lenses joined in order to minimize color and shape distortions (chromatic and spherical aberrations) that are inherent in a single lens system.

It's a pair of achromatic lens element groups, arranged symmetrically before and behind the diaphragm.

ACHROMATIC - Free from chromatic aberration. An achromatic lens is able to transmit light without separating it into colors.
ACUTANCE - A measure of the sharpness with which the film can produce the edge of an object.

A special design of lens that is highly corrected to avoid chromatic aberration by bringing the three blue, red and green wavelengths to one point of focus rather than the usual blue and green of an achromatic lens.

See also: Image, Photograph, Achromatic, Camera, Achromat