Quote:
Originally Posted by Manav
nice read and some very useful info. I need to point out though, a while back I read somewhere if one can't get long exposures then aim for multiple short ones. Not sure how effective this would be....
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Quote:
Originally Posted by swannies1983
This is my understanding but there is still quite a bit of debate on this. Scott Rosen ( www.astronomersdoitinthedark.com/) has produced some of the best DSLR images. He tends to do short subs, sometimes only 3 mins, but collects hours of data (10+). |
provided the chip temperature does not wander around, the
only SNR difference between lots of short subs and a single equivalent long one is that each read of a short sub introduces a burst of read noise. If you have a low read noise camera, short subs are entirely practical, since the overall read noise from lots of them will still end up fairly low. DSLRs will generally have fairly low read noise, so, even though they have low QE, short subs could be applicable for some targets and sky conditions. The trick is to keep the total read noise well below the shot noise and thermal noise. Short subs are not applicable to cameras with high read noise, or if doing narrow band imaging.
In the planetary imaging area, subs as short as 1/100 sec are routinely used on bright targets and an image may be assembled from many thousands of them. There is nothing inherently wrong with stacking huge numbers of short subs - the random nature of noise ensures that the signal will build up out of the noise in exactly the same way as it does with a long single exposure, provided the read noise does not intrude. It is fascinating to stack a hundred plus subs that show nothing but stars and a fairly flat noise background and find that you have a nice nebula standing out clearly in the resulting image.