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Tuesday, October 22, 2013

Defeat Chromatic Aberration


How to banish color fringes from your photos forever

Other Aberrations To Be Aware Of

There are other types of aberrations that every photographer should be aware of. Spherical aberration occurs when light rays traveling parallel to the optical axis, but at different distances from the center, don't converge on the same point. Special-effects lenses, like the Lensbaby family, exploit this characteristic to produce creative blur.

Curvature of field causes flat objects to project curved images. This is especially problematic when doing document copying or close-up photography. Macro lenses are highly corrected for this aberration. Pincushion and barrel distortion, as their names imply, cause objects to morph as if being squeezed or pinched. Very wide-angle lenses are often unjustly blamed for causing parallel lines to converge. It's true that the lens itself is sometimes responsible, but as often as not it's the photographer who fails to keep the camera and lens in correct alignment.

When light meets a small opening—the aperture diaphragm in a lens, for instance—the waves spread out. That phenomenon is called diffraction, and that's why stopping a lens down to ƒ/22 or even ƒ/16 can produce worse results than shooting at ƒ/4 or ƒ/5.6, depth of field aside. Conversely, when light hits a small object, it appears to bend around it. That's diffraction, too, but it plays virtually no role in photography except, perhaps, to explain why that speck of dust on the front element doesn't show up in the pictures.


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