Pincushioning and barrel distortion

Pincushioning and barrel distortion are types of optical aberrations that distort an image from its real-world view as the human eye would see it. Barrel distortion is characterized by a decrease in image magnification as the distance increases from the optical axis — giving the typical fisheye look where it shows a bulging effect and looks like you took the center of the image and pulled it toward you.

Pincushioning is the opposite of barrel distortion — the magnification increases as the distance increases from the optical axis, so it looks like the center of the image was pushed away from you. This effect is less common and very rare in any Canon dSLR lens, and typically only found in poor-quality telephoto lenses.

Some lenses are very true and exhibit virtually no distortion; however, some zoom lenses, in particular, exhibit some distortion at the full extent of their focal range. Some lenses distort an image by design; a fisheye lens is a prime example of this, as shown in 5-10.

Barrel distortion is the most common distortive effect you're likely to get, especially with wide-angle and fisheye lenses. A fisheye lens, of course, gives this effect intentionally; it's less desirable in a standard wide-angle lens. This image of French bread in an Algerian market was taken with an EF 15mm Fisheye lens. Photo taken with a 1D Mark II at ISO 400, 1/100 second, f/5.

Category: Science of Lenses

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