How to photograph Mars

Photographing Mars as seen in the sky is easy enough with a DSLR camera, or even a good quality compact camera or phone. You may need to use a tripod to prevent blurred images as the exposure time could be as long as a second or so, particularly with telephoto lens settings, but you should get a nice shot of Mars against a starry background.

But if you want to photograph the planet in close-up through a telescope, you need to take a lot more effort. The planet is tiny in the eyepiece, and if you magnify it enough to be able to see details it becomes quite dim.  So just pointing the camera into the eyepiece, which might work well with the Moon, isn't likely to give a good result.  However, in the past 20 years or so, amateur astronomers have been able to take images of Mars and the other planets which are streets ahead of any photographs taken on film at professional observatories in the past. Even images from the UK can be the equal of those taken elsewhere. The secret? The humble digital webcam. 

The problem with photographing the planets in particular is what astronomers call the ‘seeing’ – not how clear the sky is, but how steady it is. A planet seen through a telescope often looks as if it is seen in a stream of turbulent water – which is close to the truth, as we are looking through a slice of our atmosphere that is of varying densities and constantly in motion. As a result, views of a planet will jiggle around, with its features being constantly distorted all the time, with maybe only a fraction of a second at a time of steadiness. Couple that with the low sensitivity of film, which required exposure times of around a second, and it was rare to get a decent photograph of a planet.

But the advent of webcams in the late 1990s changed all that. They were capable of recording a video stream of images of a planet for minutes on end and the more sensitive ones gave exposures much shorter than that required for film. Most of the individual frames would be rubbish because of the varying seeing, but a few were good. Soon, software was developed which was able to select the best images out of thousands recorded on the video stream, then stack the best ones. This stack averaged out the image movements from the constantly shifting atmosphere. Because the stack was effectively a much longer exposure, made up of lots of short exposures, the amount of noise in the image was much less, giving a much smoother image that was able to be stretched and enhanced to bring out detail without amplifying the noise to unacceptable levels. The end result was an image which revealed details equalling or often exceeding that which could be seen by eye and definitely surpassing that possible with film.

Modern cameras

Today, cameras based on webcams have been designed specifically for astronomical use.  and while they cost about as much as a good compact camera, they have revolutionised planetary imaging. They have much higher sensitivity, and much lower noise than the early webcams and are capable of much greater speed — meaning many more frames captured in a given time — improving the quality of the final image. Although these cameras don’t have a large imaging area, most planets are tiny compared with nebulae and galaxies, so modest frame sizes are good enough, one megapixel being plenty. 

Camcorders or DSLRs running in video mode are an alternative, but the video stream from these is usually compressed electronically to reduce the file sizes, so they are not as good at recording fine detail.

How to start

If you want to take up planetary imaging for yourself, you will usually need a telescope with a motor drive, so that it will track the planet through the sky for a few minutes at a time. These are not outrageously expensive, and a reasonable model will set you back a few hundred pounds (see Choosing a telescope).

Suitable cameras start under £200, and can give perfectly good results. You have a choice of a colour camera, which takes the colour image in one shot, or mono cameras. These have greater sensitivity, but to take a colour image you need three separate runs through red, green and blue filters. This does give you greater flexibility in the choice of filter, but colour cameras are now preferred for most purposes. 

The method

As well as a telescope and camera, you will need a laptop or other computer near to the instrument, and usually a Barlow lens which increases the effective magnification of the telescope. This fits between the telescope and the camera. 

Once the telescope is up and running and the planet is central in the eyepiece, you replace the eyepiece with your camera and look for the image on your laptop, using the appropriate image capture software. This is where an accurate motor drive and experience with using the system pays off, because a planet such as Mars can be surprisingly hard to find in the field of view, especially if it drifts off quickly due to bad driving. Focusing is also critical. Having found the planet and centred it, you will probably want to add the Barlow lens to increase the magnification, which means refocusing.

With the planet sitting nicely on the screen, you can now record a video sequence over a period of two or three minutes, typically capturing several thousand frames on your laptop. 

Then you will use the stacking software, such as Autostakkert! or Registax, which will select the very best frames and perform the image alignment and stacking on these. You then need to use the wavelets function to process the stacked image to draw out the fine detail. Finally, if all goes well, you will see an image on your screen which far exceeds the detail visible on the individual frames or as seen through the eyepiece.

This is just an outline of the method, and advanced imagers use many other procedures to get optimum images. But the good news is that you can start with quite basic equipment and get images to be proud of not just of Mars but the other planets as well, plus the Moon and, with suitable specialist filters, the Sun. Some imagers also branch out into imaging double stars, which have their own fascination.