FILTERS

Imaging Mars in blue or infrared can reveal different aspects of the planet

You can image Mars through lters to isolate specific aspects of its appearance. What kind of camera you’re using will dictate which lters work best. For example, a monochrome camera with an RGB imaging lter can be used to create full-colour images. Blue- ltered images are useful for showing clouds in the thin Martian atmosphere. Infrared pass lters also work well with Mars, producing crisp de nition between the dark, exposed rock features, lighter deserts and polar caps. Depending on the sensor response curve, either monochrome or colour cameras may be suitable for use with infrared pass lters.

Step 1

Owing to the time constraints necessary to create a full RGB capture sequence using a monochrome camera, a filter wheel is recommended. Manual or automated versions are available. A re-focus is required after each filter change.

Step 2

A typical full capture sequence should be completed in less than four minutes. Blue typically takes longer because it appears dimmer. Using your capture software’s level indicator, aim to capture at similar peak levels of around 70-80 per cent.

Step 3

Use a registration-stacking application such as AutoStakkert! to process each capture file. The number of stacked frames depends on the sky quality but typically, for a total capture count of 3,000 frames, 10-30 per cent works well.

Step 4

Individually processed frames can be wavelet-sharpened using RegiStax. Once done, an image editor such as GIMP or Photoshop can be used to assemble the individual colour channel results into a full RGB image.

Step 5

IR-pass captures can be processed in the same manner. Using an IR-pass image to increase luminance contrast in an RGB result should be stated on the image, as it may produce a false impression of relative feature intensity.

Step 6

The final image should be presented according to the requirements of the organisation to which you intend to send it. Date, time, observer, instrument detail, location, filters used and image orientation should be shown on the image.