Step by step
Tips to boost the impact of your lunar crater images
STEP 1
Check the maximum optical zoom of your phone. Googling its make and model should tell you this. On a night when the Moon is present, point the camera at it and let it make automatic exposure adjustments. Press the shutter button. If you have some, wired headphones with volume controls may work as a remote shutter release, the volume control activating the shutter.
STEP 2
If your camera over-exposes the Moon into a bright blob of light, see if it offers a pro mode where you can control the settings. If so, hold the camera to the Moon so auto-exposure settings are made, then switch to pro mode, which should retain those settings. Reduce the ISO or exposure so the Moon’s disc isn’t over-exposed.
STEP 3
To retain foreground detail as well as the Moon, the easiest way is to photograph the Moon when the sky is still bright and the foreground illuminated. This can be done with gibbous and full Moons during the day. Alternatively, crescent Moons will appear in the evening or morning twilight, after sunset or before sunrise.
STEP 4
For more detail, consider pointing your phone’s camera down a telescope’s eyepiece. The telescope needs to be pointing at the Moon and properly focused. It helps if the mount is driven, to avoid the Moon drifting out of view. If you wear glasses or contact lenses to correct your vision, they need to be in place.
STEP 5
Bring the phone close to the eyepiece, keeping the bright light emanating from the eyepiece in view. When as close as possible, make a final adjustment to the position of the phone so the Moon’s image pops into view. Carefully press the button to take the shot. The headphone trick mentioned in step 1 is very helpful here.
STEP 6
If you fail the first time, keep trying. It takes a while to get it right. This technique is known as afocal imaging and works with other bright objects too. If you like taking photos this way, consider buying a mount to attach your phone to your telescope. They can be bought at relatively little cost, but they make holding the phone in position a great deal easier!
My image of the Plato region of the Moon was chosen as the overall winner in the ‘Our Moon’ category of the 2022 Astronomy Photographer of the Year competition, for which I felt very fortunate. The image relied on three key aspects for its strong impact: low Sun angle, favourable seeing and good composition. The Sun was rising over this particular area of the Moon when I took my image. This meant the jagged shadow from the crater’s east rim was dramatically cast nearly halfway across the smooth lava-filled base of Plato. This represented a shadow length of nearly 72 kilometres (45 miles)!
The low Sun was also important in highlighting surface detail in the surrounding region, especially the mountain peaks and narrow rilles in the upper right-hand side of the image, adding to the strong texture there. The low Sun also revealed the gentle undulations in the lava plains in the smoother lower part of the image, and created the contrasting full darkness on the left side, where that part of the Moon was still in night.
The photograph was taken on a night of very good seeing in April 2021 when the Moon was 60° high to the south. I used my 444mm Dobsonian telescope mounted on a home-built driven equatorial platform, combined with a ZWO ASI174MM mono digital video camera (recommended for lunar and solar captures due to its high speed and large chip size). I also chose a Barlow lens so the telescope was operating at f/29 – giving a magnification that nicely matched the scope’s maximum resolution to the large pixels of the camera. This camera captured 10,800 individual images over a period of several minutes, with an exposure time of 29 microseconds per frame. I used a 642nm red filter in front of the camera to further improve the steadiness of the image.
Out of the shadows
The five-minute video was processed in AutoStakkert! using the ‘Surface’ mode generally recommended for lunar and solar work. ‘Surface’ mode requires picking an obvious anchor feature first – which just had to be Plato. This anchor location was selected by holding down the Ctrl key and clicking on the crater, before then hitting the ‘Analyse’ button (see Screenshot 2).
Once the image had been analysed, the best five per cent of the total frames were selected to be stacked and an AP (alignment point) size of 200 was chosen with automatic placement. This placement divided the scene into 203 separate alignment areas; I picked a low minimum brightness of five, so that alignment areas were allocated even in the dimmest areas of the image (see screenshot 3).
Once I had clicked on the ‘Stack’ button and AutoStakkert! had done its work, quality-sorting and aligning the best frames, the final stacked image was imported into RegiStax for sharpening and contrast adjustment, as shown in screenshot 4. A low level of sharpening of 0.11 in RegiStax was applied at 100 per cent in just the first layer, using the Gaussian mode. I also added a low level of denoise (0.15) to smooth out any noise; not much was required because of the relatively long accumulated exposure duration of 15 seconds (five per cent of five minutes). As the seeing was so good, only a small level of sharpening was needed to pull out the fine detail, and this really helped to reduce the severity of any diffraction-related ringing artefacts seen around any bright edges and crater rims. It is this lack of obvious ringing artefacts around sharp features and cast against the dark shadows that separates the best lunar images from those that are not quite so good.
In RegiStax the darker areas were darkened with a bottom-end histogram stretch and the overall contrast actually reduced by increasing the gamma setting to 2.2, as shown in screenshot 4. This improved the overall look of the image, accentuating the shadow of the rim inside the crater of Plato which dominated the middle of the image.
Final processing took place in PaintShop Pro. This involved a further slight reduction in contrast, followed by cropping the edges of the image to make the most pleasing, natural and detailed overall composition, as shown in the final image on the page opposite.