The numerical aperture (NA)is:

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A term encountered in microscopy is NA.The NA of a lens can be defined as an index or measurement of the resolving power.As the NA increases,objects can be positioned closer and still be distinguished from each other; that is,the greater the NA,the greater the resolving power of a lens.The NA can also be defined as an index of the light-gathering power of a lens,a means of describing the amount of light entering the objective.Any particular lens has a constant-rated NA,and this value depends on the radius of the lens and its focal length (the distance from the object being viewed to the lens or the objective); however,decreasing the amount of light passing through a lens will decrease the actual NA.The rated NA is inscribed on each objective lens.

The Numerical Aperture (NA)is