Resolution or "spot" size of a lens. A small spot is produced by a lens having a high numerical aperture achieved using a large physical aperture and/or a short focal length. NA is equal to one-half of the reciprocal of the f-stop.

product of refractive index of medium between coverglass and objective and sine of half aperture angle of objective lens, i.e., angle between optical axis and the most inclined ray accepted by the objective lens.

Simply, a non-dimensional number that indicates the ability of a fibre or other device to receive light input. Specifically, the sine of the half angle of the acceptance or radiance cone of an optical fibre, multiplied by the refractive index of the material in contact with the fibre face.

(NA) A measure of the angular acceptance for a fiber. It is approximately the sine of the half angle of the acceptance cone.

The number that expresses the light gathering ability of a fiber. Related to acceptance angle.

The sine of half the angle over which a fiber can accept light multiplied by the refractive index of the medium containing the light. It is a function of the relationship between the refractive index of the core and that of the cladding.

The angle at wich a fibre will gather light and propagate it down the core.

A unitless number referring to the light gathering ability of a fiber and is defined as the Sine of half acceptance angle.

A measure of the light acceptance angle of the fiber.

The number representing the lens aperture of a laser pick-up device. An increased numerical aperture, 0.6 on a DVD player, allows for finer track pitch, pit length and pitch width necessary for the increased storage capacity of a DVD. Thinner substrates which diffuses less light, allow a laser with an increased aperture to be utilized while still maintaining high reading accuracy.

A number that defines the light gathering ability of a specific fiber. The numerical aperture is equal to the sine of the maximum acceptance angle.

The characteristics of an optical conductor in terms of its acceptance of impinging light. Controlled by a specific code to cladding refractive indices.

It provides a measure of the light gathering power of the system (acceptance angle). Relates to the speed of the system. In one definition, NA = 1/ (2.fl#)

A measure of the resolving power of a microscope equal to the index of refraction of the medium in which the object is placed multiplied by the size of the angle made with the axis by the most oblique ray entering the instrument, the resolving power increasing as the product increases. The effective NA varies along the length of the taper and decreases as the diameter increases.

The product of the angle formed by the cone of on-axis rays and the index of refraction of the medium in which the cone resides. With higher numerical aperture, more light will be collected. In a diffraction limited system, the numerical aperture is directly proportional to the resolution of the optical system.

The sine of half the angle over which a fiber can accept light. Strictly speaking, this is multiplied by the refractive index of the medium containing the light, but that equals one (1) for air, the normal medium for which NA is measured.

The light gathering ability of a fiber, defined as the sine of half the angle that contains 90% of the optical power that is captured by the fiber.

This is a number that expresses the ability of a lens to resolve fine detail in an object being observed. It is derived by a complex mathematical formula and is related to the angular aperture of the lens and the index of refraction of the medium found between the lens and the specimen. To get the best possible image, you should have a condenser system that matches or exceeds the N.A. of the highest power objective lens on your microscope. (note, N.A. is only important with high power microscopes).

A calculation that shows the ability of an objective lens to make fine structural detail in the specimen distinct (N.A. = n • sinα).

The sine of the acceptance angle of a fibre multiplied by the refractive index of the medium from which the light is entering (air = 1).

(NA): The light-gathering ability of a fiber; the maximum angle to the fiber axis at which light will be accepted and propagated through the fiber. NA = sin a, where a is the acceptance angle. NA also describes the angular spread of light from a central axis, as in exiting a fiber, emitting from a source, or entering a detector.

The quantity n sin θ, the product of the index of refraction of the object medium, usually air, multiplied by the sine of the slope angle of the outermost ray from an axial point on the object.

The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system (such as a lens or an optical fiber).

In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. The exact definition of the term varies slightly between different areas of optics.