BBC Sky at Night Magazine
Imaging the Red Planet
How to capture clear images of Mars when it’s high and bright
When it’s close to a favourable opposition, Mars is a great imaging target. For best results you need a planetary camera that can record many still frames in rapid succession. These can then be processed using freeware programs such as AutoStakkert! or RegiStax. The larger aperture of telescope you can use, the better. Allow your scope time to cool before use, typically 1-2 hours (large scopes may need longer). When imaging, re-focus after each filter change and ensure focus is accurate.
A colour camera or monochrome camera with filters, eg, RGB (Red, Green, Blue), is ideal. However, colour can suffer from atmospheric dispersion, an effect that chromatically blurs detail. This worsens the closer you get to the horizon, fine detail becoming less distinct and colour fringes appearing, but these effects can be reduced by using an atmospheric dispersion corrector (ADC).
Mars withstands seeing conditions well due to much of its light being in the redder, longer-wavelength part of the spectrum. If your camera is infrared (IR) sensitive, an IR-pass filter can also deliver sharp, high-contrast results. Optimum focal lengths are dictated by camera pixel size. For decent seeing, an image scale of
0.25 arcseconds/pixel is recommended. For superb seeing, 0.1 arcseconds/pixel may also work. The best focal length can be calculated from: FL = (Ps x 825) for 0.25 arcseconds/ pixel, or FL = (Ps x 2060) for 0.1 arcseconds per pixel; where FL = telescope focal length (mm) and Ps = pixel size (microns).
Close to opposition, Mars rotates 0.25 arcseconds in about 5 minutes and 0.1 arcseconds every 2 minutes. Consequently, cumulative capture times (eg, total for R+G+B) must be shorter to avoid rotational motion blur.