The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the cone is located. Note: The NA is generally measured with respect to an object or image point and will vary as that point is moved. 2. For an optical fib [..]

An index to measure the resolution of a microscope's objective lens. Defined as a numeric value, it represents the range over which the objective lens can gather light. The greater the numeric va [..]

(N.A.): 

sine of the maximum angle of an incident beam of some optical device, or the sine of the acceptance angle of a waveguide or fiber

The numerical aperture of an optical component (such as a lens or fiber) is a unitless quantity that characterizes the range of angles through which the component can emit or accept light. A fiber with a higher value for NA, for example, will have a larger acceptance cone for incident light. All Ocean Optics standard glass fiber optic cables have a [..]

The number that expresses the light gathering ability of a fibre.

The measure of the diameter of the aperture (opening) compared to the focal length of the lens and it indicates the resolving power of a lens. A lens with a larger numerical aperture will be able to visualize finer details than a lens with a smaller numerical aperture.

The sine of the vertex angle of the largest cone of meridional rays that can enter or exit an optical system. In other words, it governs the amount of light entering or exiting a system. It is inverse [..]