Chromatic

AberrantBehavior
Photographers read about (and often fret about) all sorts of optical phenomena when lens shopping. One of these ischromatic aberration. It's not often an issue, but it is seen occasionally. It is caused when a lens is unable to bring all colours to the same point of focus. The effect seen is colour fringing, usually most noticeable around brightly coloured objects, and usually seen with long focal length or very wide lenses. The red/magenta end of the spectrum is where its effect is most pronounced.
If you buy a lens that is really apochromatic (APO) the problem will have been well corrected. These lenses are expensive though, because to bring all colours to a common focus requires the use of fluorite or some other form of ultra-low dispersion glass.(Incidentally, just because a lens has the wordsAPOin its name doesn't necessarily mean that it's truly an apochromatic. The designation has been abused by quite a few manufacturers. Caveat Emptor.)
If you've read my revie...