Does shutter speed affect noise, or is image noise mainly determined by ISO?
Asked 11/21/2012
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If aperture stays constant and two shots have the same overall brightness, will a high-ISO/fast-shutter image have the same noise as a low-ISO/slow-shutter image? Assume a modern DSLR, tripod, and a static subject so motion blur is not a factor.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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Image noise in a properly operating DSLR will be affected by shutter speed, but not in the linear relationship the question implies. In decreasing order of impact, image noise is a factor of:
- Amplification applied to the sensor cells (higher ISO increases noise)
- Thermal noise (hotter sensor is noisier)
- Duration of exposure (longer the capture, more the cumulative random pixels lit up)
Duration related noise is also interrelated with thermal noise, since keeping the sensor powered for longer will cause more heat to be generated.
Overall, in a given shooting environment, increasing ISO has the greatest detrimental effect, going by empirical evidence from a fair bit of night photography done using a Canon 1D Mark III, Canon 5D Mark II, and a couple of non-SLRs, a Minolta DiMAGE A2 and DiMAGE A200.
Summer evening shots also seem to have greater visible noise (I see more random red dots than other colors, oddly) than cold winter evening shots.
Originally by user11995. Source · Licensed CC BY-SA 4.0
user11995
13y ago
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Not exactly. On a modern DSLR, noise is affected much more by ISO than by shutter speed.
If aperture is fixed, a lower ISO with a longer shutter speed will usually give cleaner results than a higher ISO with a shorter shutter speed, assuming the subject and camera are steady. Higher ISO mainly means more amplification of the sensor signal, which makes noise more visible and also reduces dynamic range.
Shutter speed can matter, but usually only a little by comparison. Very long exposures can add noise through sensor heating and exposure-duration effects, so extreme long exposures may become noisier. But in normal situations, that increase is modest compared with the penalty from raising ISO.
Also, noise fundamentally depends on how much light is actually collected: more photons generally means better signal-to-noise. So if you can keep the shutter open longer without blur, using a lower ISO is typically preferable.
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