How much ISO noise can be rescued in post for extreme moon shots?
Asked 2/2/2020
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I photographed the moon with a Canon 5D Mark II and a 1000mm MTO-11CA, then added a Kenko Pro 300 3x teleconverter for more reach. That effectively gave me a very slow, very long setup, and I ended up shooting around ISO 25000 at 1/2500s on a tripod. The results are very soft and extremely noisy.
I tried RAW and JPEG processing in tools like digiKam and RawTherapee, but noise reduction barely helped. In a case this extreme, how much detail can realistically be salvaged in post? Are there any useful techniques for lunar images this noisy, or is the better answer to avoid this setup and crop instead?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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The moon is really a special case, because it is mostly grey. So you can remove chroma noise by just picking a channel (green, usually). This also removes some of the chromatic aberrations on the edges (when they are sharp, which isn't he case here).
You can also average the three color channels: copy the image to obtain three layers, and using the channel mixer, make a layer be (R,R,R), another one (G,G,G) and one (B,B,B). Then average them by setting the opacity of the top one to 33.3% and the next one to 50% (bottom stays at 100%).
If you want to restore the colors, you can blur the initial image and re-apply it in color mode over the clean image.
I also tried a median filter but the results are a bit fuzzier.
IMHO you have completely overdone it. The moon moves by its diameter in 120s. In your picture the diameter is about 4200px so it takes 1/35s to move by one pixel. 1/100s would give you a huge safety margin, and would still let you use much more reasonable ISOs.
Originally by user75947. Source · Licensed CC BY-SA 4.0
user75947
6y ago
0
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Not much. In this case the main problem isn’t just ISO noise—it’s the capture setup. A 1000mm lens with a 3x teleconverter is effectively around 3000mm and very slow, so diffraction, lens softness, focus difficulty, and atmospheric/thermal effects all hurt sharpness before noise reduction even starts. If detail was never resolved, denoising can’t restore it.
What you can do:
- Remove chroma noise aggressively, or convert to black and white. The moon is mostly gray, so color information matters less.
- You can even build a grayscale image from the cleanest channel, often green, or average the RGB channels to reduce color noise.
- Replace the background with pure black/dark gray to hide banding and ugly noise.
- If desired, sharpen carefully after noise reduction, but don’t expect major recovery.
Best practical advice: skip the 3x teleconverter. On an 18–24MP body, a crop from the bare lens will often look sharper and let you use a much lower ISO. So yes, some cleanup is possible, but this image is close to a lost cause because the softness and diffraction are baked in.
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