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CCD vs dSLR
Now that I've established that my newly-acquired mono CCD is still broken, albeit in a seemingly different way, I'm taking a step back and revisiting the dSLR vs CCD decision.
I'm interested in hearing why purpose-built CCD systems are considered better than consumer dSLR cameras for the purpose of astrophotography. Previously I had thought the following factors supportive of CCD:
1) Lower noise (due to cooling)
2) Greater dynamic range
3) Sensitivity, in particular to H. alpha
I'm now questioning points 1 and 2 after noticing something. I had a quick look around for some information on the OSC QHY 8 camera, and discovered that it actually has the same sensor as a Nikon D50. This has undermined my confidence in CCD, particularly point 2.
My question is now, why would I buy a OSC QHY 8 over a Nikon D50? The answer seems to be only because it's cooled and because of the greater spectral sensitivity. Of course I could have a dSLR modified to increase sensitivity around 650nm so that nebula are more easily captured, so that's a reasonable solution to point #3.
This leads me to the following question: What would I be losing out by using a modified Nikon D5100? It has greater dynamic range than the D50, I'd gain back the "missing" spectral sensitivity, I'd have a sensor that generates less noise and could conceivably out-perform it if I built a little cooler box for it.
I suppose this is why most people don't bother with OSC CCD cameras and instead use mono CCD cameras. But then what is the advantage of mono?
I've seen the argument that mono CCD are more sensitive due to the lack of a bayer CFA, but I don't understand that; maybe I'm missing something. The reason that I find that confusing is because it seems to me that's actually a problem with reduced resolution rather than sensitivity.
If all the bayer CFA does is put a colour filter over four pixels so that it's 1 red, 2 green, 1 blue, then how does that affect sensitivity? Surely that just means that instead of capturing the full resolution in (for example) red, you're actually capturing less and the rest is "recovered" (guessed) by software interpolation? This would mean that if you were prepared to sacrifice some resolution (and lets face it, these new dSLR have plenty to spare in comparison to available CCD) you wouldn't be giving up much, if anything... hell, without doing the math you might even still be ahead.
So, what am I missing?
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