numerical aperture

nounMicroscopy.

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. Abbreviation: N.A.

Origin of numerical aperture

First recorded in 1875–80

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

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.
Inside the machine that saved Moore’s Law | Clive Thompson | October 27, 2021 | MIT Technology Review
It is generally assumed that a good objective requires an illuminating cone equivalent to two-thirds of its numerical aperture.
The Elements of Bacteriological Technique | John William Henry Eyre

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