Most lenses contain a diaphragm, a thin light-blocking plate or interleaving set of adjustable plates. The diaphragm contains a small hole, the aperture, which is adjustable in size and allows the photographer to control the amount of light entering the camera. Apertures are indicated by the f stop value, which is a relative value and does not indicate the actual size of the aperture hole.
Really crummy cameras - disposable cameras being one example - have fixed apertures that cannot be adjusted.
cf. diaphragm, f stop.
Entry last updated 2002-05-07. Term 69 of 1487.
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