pincushion distortion

irregular image produced when axial magnification is greater than peripheral magnification. See: Petzval surface.

Farlex Partner Medical Dictionary © Farlex 2012

pin·cush·i·on dis·tor·tion

(pin'kush-ŭn dis-tōr'shŭn)

Irregular image produced when axial magnification is greater than peripheral magnification.
See: Petzval surface

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

distortion

Aberration of an optical system resulting in an image which does not conform to the shape of the object, somewhat resembling the image viewed through a cylindrical lens. This is due to an unequal magnification of the image. Distortion can be barrel-shaped (barrel-shaped distortion) in which the corners of the image of a square are closer to the centre than the middle part of the sides; or pincushion (pincushion distortion) in which the corners of the image of a square are farther from the centre than the middle part of the sides (Fig. D10). Example of barrel-shaped distortion: a square object seen through an uncorrected negative spectacle lens. Example of pincushion distortion: a square object seen through an uncorrected positive spectacle lens. See correction; fisheye lens; sine condition.

Fig. D10 Distortion (O, object; A, pincushion distortion; B, barrel-shaped distortion)

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