numerical aperture

American  

noun

Microscopy.

1. 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 sine of the angle made with the axis by the most oblique ray entering the instrument, the resolving power increasing as the product increases. N.A.

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Etymology

Origin of numerical aperture

First recorded in 1875–80

Example Sentences

The latest version, made by ASML, performs high numerical aperture extreme ultraviolet lithography.

From The Wall Street Journal • Nov. 3, 2025

Although better sectioning is possible by using a higher illumination numerical aperture, this creates a shorter depth of focus that reduces the system's usable field of view.

From Science Daily • Mar. 20, 2024

The numerical aperture of the optical fiber can be determined by using the angle αmax.

From Textbooks • Aug. 12, 2015

While the numerical aperture can be used to compare resolutions of various objectives, it does not indicate how far the lens could be from the specimen.

From Textbooks • Aug. 12, 2015

It is generally assumed that a good objective requires an illuminating cone equivalent to two-thirds of its numerical aperture.

From The Elements of Bacteriological Technique A Laboratory Guide for Medical, Dental, and Technical Students. Second Edition Rewritten and Enlarged. by Eyre, J. W. H. (John William Henry)