Quote:
Originally Posted by gregbradley
Dan, I think that discussion was about DSLRs not astro CCDs. The main difference being 9 micron pixelled CCDs have 100,000 electron full well capacity (how many electrons the pixel can hold before spilling over).
DSLRs well capacity would be less. Also they are quite a bit less sensitive than the CCD's which are usually 50% at the low end and up to 77% or more at the high end for CCDs. Also having a colour filter array this makes them even less sensitive.
ISO simply is an amplifier of the signal. Its like turning the sound up on your stereo. It does not add anything merely magnify what is there.
The whole point there is getting the faint details above the noise of the camera. At what point that occurs is the question. From my experience of imaging faint objects hundreds of times, that will not occur in 45 second-4 minute subs with a basically not very sensitive DSLR.
The M101 example he posted proves the point. There is a lot more faint detail missing from that image. Its impressive from the standpoint of a DSLR captured image but not impressive compared to a reasonable CCD image of similar duration from an 8 inch scope. It looks black clipped as he mentions it probably was.
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All good points but the OP didn't specify this as a "CCD only" discussion
. In fact, there's another
thread on the first page purely discussing CCD and exposure length.
Obviously, if you compare CCD vs DSLR, CCD will win hands down. But the advantages of long subs over short subs is still up for debate.
Quote:
Originally Posted by gregbradley
DSLRs are great for bright objects but the dim ones they are unsuitable because of the above.
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I disagree. You only have to look at Scott's work to appreciate what can be achieved with a modded dslr under dark skies. Just check out some of his work
M81, M82 and the Integrated Flux Nebula (ok, ten minute subs for this one).
Witch head (5min subs @ ISO800)
Leo Triplet, including tidal stream of NGC 3628 (only 3 min subs for this galaxy)
Whirlpool Galaxy (5 minute subs)
He has many more examples of what can be achieved using short subs with a dslr. Granted, the amount of hours he puts in to get these images is much more than one would do with a CCD camera, but some of his images easily surpass CCD images.