Astrophotography
Lunar photography for beginners.
RECOMMENDED EQUIPMENT DSLR or high frame rate planetary camera, telescope, tracking mount
The Moon is a beautiful celestial object and a perfect target to start with if you’ve been given astronomical imaging kit for Christmas. There are all sorts of different ways to image it and many levels of detail that can be attempted. One of the most rewarding ways to photograph the Moon is to attach a camera to your telescope, using the scope as a supertelephoto lens. Adaptors can be obtained for most types of camera that will enable them to be coupled directly to the eyepiece holder of your scope.
Even if you don’t have a specialist adaptor, a telescope fitted with an eyepiece, focused on a bright Moon can act as a source for devices such as smartphone cameras. With a bit of practice, it’s possible to carefully point the phone’s camera at the bright image presented in the eyepiece and take a shot. The camera will work out the settings for you and often give a surprisingly good result.
A DSLR attached to a telescope is another way to produce great images of the Moon. Set the camera to manual, select a low ISO value of say 100-200, a short exposure and take the shot. A remote shutter release is highly recommended, as it will help prevent the scope shaking when you press the shutter button. The same thing can be achieved by setting the delay timer if you don’t have a remote shutter release.
How short the exposure needs to be depends on factors such as the current phase of the Moon and the focal length of your scope. Start out with an exposure of 0.5 seconds and review the results. If the image is overexposed, shorten the exposure; if it’s underexposed, increase the exposure. A tracking mount is recommended to get the sharpest shots, but if you don’t have one, increasing the ISO should allow you to keep exposures short enough to avoid significant motion blur. This blur is due to the Earth’s rotation. Just be aware that increasing ISO will also increase noise.
Experienced lunar photographers can determine whether the shot they’ve just taken is over- or underexposed by assessing the image as it appears on their camera’s review screen. For lessexperienced imagers, however, there’s a more surefire method of checking your results via the camera’s histogram display. The process for doing this is covered in the step-by-step guide, opposite. Focus is also very important and for a stills camera it’s important to realise that even if you’ve spent ages focusing on those dramatic and sharp lunar shadows, it’s still possible to take blurred shots. There are many reasons why this happens including inadvertently knocking the telescope, a brief gust of wind or simply a rather turbulent region of air between you and the Moon. For this reason, it’s always recommended that you take many shots in quick succession. More often than not, what looks sharp on the back of the camera may turn out to be quite soft when viewed on a computer screen. Taking lots of shots increases the chance that you’ve caught at least one or two that are sharper than the rest. For close-up, highly magnified shots, a high frame rate planetary camera is recommended. In many ways this does a similar thing, in that it takes lots of shots in rapid succession, hoping that some of them will appear sharp. The resulting movie sequence can be processed using one of the excellent freeware registration-stacking tools that are available online.