pincushion distortion

Definition: Lens aberration that causes a square to be projected pincushion-shaped i.e. the sides cave in so the middle portions are closer to the centre than the outer portions. * It is a positive distortion i.e. image magnification increases with increasing field angle. * In photographic use, a distortion of greater than about +3% is regarded as unacceptable for professional-quality work but for certain applications e.g. flat-copying even that amount is excessive, and should be less than 0.1%. * Also seen in monitors.

Related Terms: curvilinear distortion, barrel distortion

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