On examining some of my recent pictures i notcied a strange colour effect. Edges of objects had a strange purple fringing to them. This was most noticeable on shots taken with the telephoto lens on full zoom:
I was worried there was something wrong with my camera but it turned out this is a common problem called chromatic abberation. It often happens in images with strong contrast and is caused by different colours being refracted by a lens by different amounts. So, for example, the red wavelength is refracted more than other colors and lands on a different part of the sensor. It is common in poor lenses and especially zoom lenses at high magnification. My telephoto wasn't cheap to me but with a good quality L lens(canon's 'luxury' line of lenses) costing around £1000 it is all relative. Anyway the problem isnt that bad and is kept to a minimum by avoiding high contrast subjects and trying not to zoom in too much. Photoshop also has a filter that attemps to remove the problem --with varying results.
I'm going to try to get down to London Zoo this weekend.