THIS MONTH: LENS ABERRATIONS

THESE days, camera lenses are very well corrected for optical aberrations. The quality of corrective lens elements and multi-coatings mean that even zoom lenses with complex designs can produce results as crisp and colourful as older primes.

That doesn’t mean they’re perfect. Chromatic aberration still continues to plague digital photos, for instance. This phenomenon is similar to the effect you see when light passes through a prism, with the different wavelengths of light becoming separated. In a digital image, this manifests as a coloured halo around high-contrast objects, and this can make images appear less sharp than they ought to be. More advanced lenses use lowdispersion elements that reduce the degree to which the different wavelengths are dispersed. Cheaper lenses don’t have