relative aperture

noun

: a measure of the angle of the cone of light rays from an object that traverse an optical system
specifically : the effective aperture of a camera lens expressed as a fraction of its focal length with the symbol f being used instead of 1 as the numerator or expressed as the ratio of the effective aperture to the focal length
a lens having an effective aperture that is 1/45 of its focal length has a relative aperture of f/4.5 or 1:4.5

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“Relative aperture.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/relative%20aperture. Accessed 1 Feb. 2023.

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