fall-off

Definition: (1) Loss of illuminance in the corners of an image as projected by a lens in e.g. a camera or a projector. (2) Loss of light towards the edges of a scene that is illuminated by a light source whose angle of illumination too small to cover the required view e.g. electronic flash with normal coverage used to light a very wide-angle of view. (3) Loss of image sharpness and lumination away from the centre of a scanner, the length of whose array sensors is less than the width of the scanned area.

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