focal ratio

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  • noun

Synonyms for focal ratio

the ratio of the focal length to the diameter of a (camera) lens system

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References in periodicals archive ?
These are often zoom lenses where the focal ratio increases with the focal length and it is important to determine actual speed for a given focal length.
One of comparable thickness and focal ratio would weigh five times more - 100 tons.
Many spectroscopic applications require high performance optical fibers that transmit light over a broad spectrum and demonstrate minimal focal ratio degradation.
The optical system is equipped with a focal reducer to yield a focal ratio f/6.
The light only traversed around half the length of the tube before reaching a focus from the primary mirror, equating to a much shorter focal length, and in turn a much faster focal ratio and larger field of view.