field stop

Definition: Mask or aperture that determines the size and shape of the image.* It is placed close to the focal plane of an optical system. * E.g. the film-gate of a camera. Vignettes on life In contrast to a field stop, which produces a sharp margin to the image, vignettes such as the heart-shapes and ovals favoured by soppy portraitists, all project a fuzzy outline. Vignettes are strictly speaking also stops but are place in front of the lens. This means the sharpness of the outline increases with larger f/number.

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