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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.
DSLRs are great for bright objects but the dim ones they are unsuitable because of the above.
I definitely see a gain in 15 minutes over 10 minute subs. Its subtle but its there. Tracking has to be good though as elongated stars are worse than not getting some tiny faint detail.
Greg.
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