Does stacking multiple high-ISO Milky Way shots reduce noise and reveal more detail?
Asked 3/5/2016
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I shoot stars and the Milky Way with a camera that tops out at ISO 1600. I usually make a single 20–25 second exposure, but I’ve read that stacking multiple images can reduce noise. Will stacking also help bring out more real detail in the final image, or does it mainly just smooth noise? If I want to try this, should I use shorter individual exposures than my usual 20–25 seconds, and roughly how many frames are typically useful? I’m also aware the stars move, so I assume alignment is required.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
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Yes, image stacking will both reduce noise and let you see more of what's there. In fact, even the Hubble Space Telescope does something like this.
For timing, you can use the rule of 600 (or rule of 400 if you're on a crop sensor), to figure out the maximum length to expose your shots without having trails. Once you know that you can experiment with shorter durations. Obviously, the longer each exposure is, the more light it will collect.
Note that you'll also have to deal with the movement of the stars. I'm not up on my astrophotography software, but you'll need to use some sort of motion tracker to align the images, otherwise you'll end up with star trails combining a bunch of exposures together! (I've used Motion and After Effects for tracking in the past because I happen to have them.) Or you'll need a heliostat or other sky tracking device to mount your camera on.
Originally by user22895. Source · Licensed CC BY-SA 4.0
user22895
10y ago
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Generated from our catalog & community — verify before relying on it.
Yes—stacking can reduce noise and make faint star and Milky Way detail easier to see. It doesn’t create new detail that wasn’t captured, but by improving signal-to-noise ratio it can reveal real detail that was buried in noise in a single frame.
Use exposures short enough to avoid obvious star trailing. A common starting point is the rule of 600, or more conservatively the rule of 400 on a crop-sensor camera, to estimate the longest shutter speed before trails become noticeable. Once you know that limit for your focal length, you can experiment with exposures at or below it.
Longer individual exposures collect more light, so don’t shorten them more than necessary. Instead of one long frame, take multiple frames at the same settings and stack them.
How many? More frames generally helps, with diminishing returns as you add more. There isn’t one “best” number—take as many as practical.
Important: the stars move, so the images must be aligned for the sky before stacking. Otherwise the result will blur or produce trails.
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