As the cost of large-sensor cooled CCD imaging systems has, until recently, been very high, many astro-imagers wanting to make wide-field images of the sky have taken to using DSLR cameras. With their inbuilt colour filters forming a Bayer matrix above the sensor, colour images are easily produced without the cost of the filters and filter wheels that are used with the majority of CCD cameras − not to mention the increased image processing time that is then required afterwards.

There is no doubt that Canon DSLRs have, up to now, been the choice of virtually all astro-imagers, with Canon providing free software to allow computers to remotely control their cameras and download the resulting images. Two more sophisticated programs to control Canon cameras are ‘Astro Photographic Tool’ (APT), which is freeware, though a small payment is (rightly) requested, and ‘Backyard EOS’, which is somewhat more expensive. Both allow sequences of exposures to be made so that the imaging system can be left unattended. They also record the sensor temperature for each exposure, which can be very useful if ‘dark frames’ are to be subtracted in the image processing software rather than in the camera, as will be discussed later. For example, APT can add the sensor temperature to the file name as in ‘L_3745_29C’, where L indicates a light frame.