High Quality Content by WIKIPEDIA articles! 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. In microscopy, NA is important because it indicates the resolving power of a lens. The size of the finest detail that can be resolved is proportional to ?/NA, where ? is the wavelength of the light. A lens with a larger numerical aperture will be able to visualize finer details than a lens with a smaller numerical aperture. Lenses with larger numerical apertures also collect more light and will generally provide a brighter image. Numerical aperture is used to define the "pit size" in optical disc formats.

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