numerical aperture

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.

Word History and Origins

Origin of numerical aperture¹

First recorded in 1875–80

Example Sentences

It will be able to focus EUV light to an even sharper degree thanks to what’s known as a higher numerical aperture, allowing it to etch components that could be under 10 nanometers wide.

From MIT Technology Review

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

From Project Gutenberg