The Moon is a pockmarked lump of rock, battle-scarred from a multitude of past impacts. Some of these were so large that they deformed the lunar crust, depressing and cracking it so the resulting depressions infilled with lava.
These huge basins form the lunar seas or lunar maria, and they can be extensive in area. As well as the large basins, there are many craters of all shapes and sizes that make great imaging targets.
For more advice, read our guide on how to photograph the Moon.
More Moon projects:
- How to see crater Clavius on the Moon
- Create a mineral Moon astrophoto
- 10 of the best features to observe on the Moon
Photograph the Moon with a smartphone
The larger lunar craters can be imaged with basic kit like a smartphone. All you need to do is to point the phone’s camera down the eyepiece of a telescope.
Known as afocal imaging, this technique produces good results, often exceeding the results that used to be produced by coupling a DSLR to a scope.
As afocal imaging requires you to point your scope at the Moon, a tracking drive is recommended as it alleviates the need to continually shift the scope’s position to keep the Moon in view. You’ll have enough to do lining up the camera.
Focus is critical and it needs to be done for corrected vision. If you wear glasses, focus with them on. Use a low- to mid-power eyepiece and centre the Moon in the field of view.
Next, activate your smartphone’s camera. Most camera apps have a pro or manual mode that allows you to control the camera settings, which is great if you’re feeling confident. If not, leave the camera on automatic.
The Moon is bright enough to activate the camera app’s auto-settings and 75% of the time the values selected will work just fine.
It helps to develop a lining-up technique. One way is to hold the phone’s camera some way off the eyepiece, or you could build your own smartphone holder (see image below).
Have a look at what else is available in our guide to smartphone astrophotography gadgets.
You’ll need to be able to see the eyepiece with a bright light (the Moon) coming from it. Then, slowly but surely, move towards the eyepiece keeping the bright area in view.
It can take a while to get this right, and bear in mind you need to a) keep the camera flat to the eyepiece and b) eventually press the shutter button.
The second step is easier if you use a remote shutter release. A smartphone’s wired headphones often mimic this action; plug them in and press the volume up button.
Photograph the Moon with a planetary camera
The best crater images are obtained using a high frame rate planetary camera attached to the eyepiece end of a telescope.
There are certain techniques that will give you optimal results, and we’ve shown some of these in our step-by-step guide below.
How small you can go in terms of crater diameter is determined by the size of your scope: the greater the aperture, the smaller the feature you can resolve.
The stability of the atmosphere will also have an effect, the best results being achieved when seeing is steady. Forward planning can help here (see below, step 4).
With so many lunar craters to choose from, this project is a great chance to get acquainted with our nearest neighbour in space using whatever equipment you have to hand.
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Photograph craters on the Moon: step-by-step
- Telescope on a tracking mount
- Smartphone for afocal imaging
- DSLR/MILC camera
- High frame rate planetary camera
- Optical amplifier
- Red or infrared pass filter
The simplest method for imaging the Moon with a scope is to point a camera down the eyepiece using the technique of afocal imaging (as described above), which works well for smartphones. Getting everything lined up can be tricky, so practice is advised. Also, it’s best to image the Moon when it’s not close to full phase.
If you have a DSLR or MILC camera, fit an adaptor onto the connecting ring of the camera’s body – where the lens would usually connect – and attach an eyepiece barrel for insertion into your scope. A 2-inch barrel will avoid light cone clipping, which can lead to vignetting (a darkening at the edges) in images.
For high-resolution crater imaging, a high frame rate planetary camera is best. Controlled by an external computer such as a laptop, modern high frame rate cameras can typically capture from many tens to hundreds of frames per second. This helps to combat seeing-related issues, such as atmospheric distortions.
Bear in mind that seeing degrades with low altitude and the Moon appears highest when due south. As wind direction affects low-level seeing, note the seeing for different wind directions to predict when conditions may be steady. To avoid the jet stream use a forecast service (Google: ‘jet stream forecast’).
Use a Barlow lens or other such optical amplifier to increase the image-scale. The optimum focal length to aim for under average seeing conditions is given by 825 x Ps, where ‘Ps’ is the size of your camera’s pixels in microns, Under good to excellent seeing use 2060 x Ps. Use an optical amplifier to get you close to these values.
Longer wavelengths are less affected by seeing. Imaging with a mono camera through a red or infrared pass filter may produce steadier results. Some colour cameras have excellent infrared sensitivity and can be used this way too. Aim to capture at least 1,000 frames. Process in a stacking program and tweak the result.
Pete Lawrence is an expert astro imager and a co-presenter of The Sky at Night. This guide originally appeared in the January 2021 issue of BBC Sky at Night Magazine.