Quote:
Originally Posted by luigi
The Signal to Noise ratio improves as you increase the ISO. This is because the sensor read noise is not amplified as the signal is.
So as long as the dynamic range is enough you should shoot at the highest possible ISO for a given exposure time.
For most DSLRs this stops making sense beyond ISO1600 but up to 1600 the higher the better.
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I would have thought that astro photos all have a very high dynamic range. The difference in brightness of stars compared to DSO objects is very high. As long as you are happy losing almost all of the colour data for stars then I suppose this is ok.
I'm also curious about the read noise.
When is the gain (or ISP amplification) applied?
I thought that the order was that each line of the ccd is read then the gain is applied. This would mean that the read noise is also affected by the gain.