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System Throughput, f/#, and Numerical Aperture

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System Throughput, f/#, and Numerical Aperture

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  • Author: Gregory Hollows, Nicholas James
The f/# (pronounced “F-number”) setting on a lens controls overall light throughput, depth of field (DOF), and the ability to produce contrast at a given resolution. Fundamentally, f/# is the ratio of the focal length, (f), of the lens to the effective aperture diameter In most lenses, the f/# is set by turning the iris adjusting ring (See The Anatomy of a Lens). This movement opens and closes the iris diaphragm inside.

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