The characteristic of an optic conductor in terms of its acceptance of impinging light. "Degree of openness", "light gathering ability" and "angular acceptance" are terms describing this characteristic. Mathematically, numerical aperture equals the sine of one-half of the acceptance angle.
Describes the angle in a cone of light emitted by the condenser and accepted by the objective of a microscope; the index of refraction of the medium in which the image lies multiplied by the sine of the half angle of the cone of light.
(N.A.) a term representative of the angle included by a cone of light accepted by the objective of a microscope. The higher the N.A., the greater the resolving power.