Numerical Aperture

Numerical aperture (NA) is an optical measurement used in microscopy, optics and ophthalmology to quantify the light gathering ability of an optical system or lens. It is the angle formed by the light cone or light bundle that enters the system, and which is the highest angle at which light can enter the system without being rejected or blocked. NA is a key factor in determining the performance and resolution of an optical imaging system. The higher the NA, the higher the resolution of the system and the more light it can collect. This is useful in applications such as low light imaging, scanning microscopy, endoscopy and fibre optics.