Are the dots around Saturn stars or just noise in a single heavily edited shot?

Asked 12/3/2024

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I photographed Saturn last night with a Nikon D3500 and Tamron 150-600mm G2 at 600mm, ISO 400, f/8. In the original image I could only see one or two stars, but after boosting exposure and whites a lot, many bright dots appeared around Saturn. This is a single frame with no stacking. Are those dots likely real stars, image noise, or a mix of both? How can I tell?

Originally by madhur3u. Source · Licensed CC BY-SA 4.0

madhur3u

1y ago

2 Answers

16

Yes.

That is to say, there is almost certainly some of both in your image. After all, there are more dim stars in the sky than bright ones. The brighter we expose, the more stars will show up. Likewise, the brighter we amplify what our sensor captures, the more stars will show up. But noise will also be amplified by the same amount.

If you really stop and think about it: no matter what your exposure is, there will always be some (hopefully very dim) stars that are the same brightness as the read noise in your image. Unless you intentionally take a frame with camera motion or slight focus blur, so that the stars are blurred but the noise will continue to be sharp points, it's pretty hard to tell the difference. Defocusing only works so far, though, because if you defocus too much you just spread the light from the dimmest stars you capture at a particular exposure level so much that they do not register at all. Long enough exposure without any tracking movements never lies. If the stars are streaks, they're not noise. If the stars are streaked, anything that is still a point is noise.

Originally by Michael C. Source · Licensed CC BY-SA 4.0

Michael C

1y ago

0

AI Answer

Generated from our catalog & community — verify before relying on it.

They’re most likely a mix of faint stars and amplified noise, but in a single heavily brightened frame it can be very hard to separate the two.

Boosting exposure/whites in post makes both real stars and sensor/read noise more visible. In any night-sky image, some very dim stars will be near the same brightness as the noise floor, so single-pixel dots can be ambiguous.

A good way to check is to compare the area around Saturn with a planetarium app such as Stellarium, set to the exact date/time and location of the shot. If the brighter dots match the chart, they’re real stars.

That said, if many dots have become very bright or even saturated white after editing, they are unlikely all to be stars. In such a small field around Saturn, you would not normally expect a large number of stars bright enough to saturate in the same exposure unless the background was pushed very aggressively.

So the safest conclusion is: some may be real stars, but many of the brightest dots are probably noise or processing artifacts. Stacking multiple frames is the best way to improve confidence and reduce noise.

UniqueBot

AI

1y ago

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