A software option

Steve Richards suggests an Atmospheric Dispersion Corrector to do away with colour fringing in planetary images (Scope Doctor, October 2018). While this is the ideal solution there are a couple of software measures that can partially solve the problem – with the benefit of being absolutely free!

On the Wavelet screen of the freeware program RegiStax there is an ‘RGB align’ function (using red, green and blue light elements) that will remove the worst of the fringes and improve the overall image.

If your photo manipulation program includes an option to split an image into separate R, G and B channels, you can create a selection around each of the resulting greyscale images and nudge them separately so that, when recombined, they now line up. In effect, this is similar to the RegiStax method but it also allows you to individually tweak the R, G and B channels. Bob Humphrey, via email