I appear to be getting a thin red outline around high contrast areas in some of my pictures such as tree branches against a light sky.

This is more than likely due to a phenomenon called ‘bleeding’ on your image sensor. This is where light from one pixel bleeds over to an adjacent pixel which is designed to detect a different colour. This is a disadvantage to Bayer type sensors and the result is a thin red outline around dark areas …

I have an old Sigma 70-300mm lens which I gather needs ‘re-chipping’ to work on my new Canon digital SLR. Can this be done?

The majority of lenses we can rechip. However there are a few older lenses which we are unable to re-chip due to parts no longer being available. In order to answer your question, we need to determine which 70-300mm lens you have. If you look at the lens, is the Macro switch held on by …