A hot question.
Check out these 2 images:
http://www.pampaskies.com/gallery3/D...ects/B33-Flame AP130GT and Canon 1000D cooled and modified
http://www.pbase.com/gregbradley/image/92757065 mine with STL11 and AP140
The first is by Ignacio of Argentina and the 2nd one is mine from remote NSW.
His was taken with AP130GT and modified and cooled Canon 1000D and taken near Buenos Aires (it said from rural skies in the post title).
Mine was taken in rural skies in NSW and an AP140 and SBIG STL11.
Not a huge difference is there? Subtle perhaps, a bit richer in mine perhaps, perhaps a bit more resolution in mine. But I wouldn't say there is a lot in it.
But thats not a regular DSLR that has been modified to be cooled and the standard filter replaced.
So the advantages as I see it of each are:
DSLR:
1. Cheap although these days the price difference between CCDs and DSLRs has narrowed especially a cooled DSLR and CCD.
2. Doesn't need a computer so its more portable and less cables and gear. Although you virtually need a computer anyway for these types as I suspect the cooling needs a computer (not sure) and you need an autoguider which are usually controlled by a computer.
3. One shot colour is a bit easier to process.
4. Each shot taken is an image in itself versus mono CCD where you need 4 filtered images luminance, red, green and bue to get a colour image so if there's regular bad weather one shot colour makes a lot of sense.
5. A lot of software support and a lot of imagers using them for backup.
CCDs:
1. Lower noise because they are cooled. The cooling is regulated so you can match the light exposures with a dark exposure to subtract the dark noise. Cooled DSRLs may not be temperature regulated well enough to do that and use a special kind of dark which is not as perfect to achieve a clean up.
2. More sensitive. Unless we are comparing to one shot colour and then they are much the same.
3. Mono has higher resolution.
4. Small CCD cameras are lighter.
5. More resolving electronics. Most CCD cameras are 16 bit and most DSLR are 10, 12 or high end 14 bit.
6. More flexible. You are limited to Ha imaging with a DSLR in narrowband. The other narrowband won't work well enough. And Ha is not as good as a mono CCD (it takes 4 pixels on a colour sensor to make a one shot colour versus every pixel in mono, in one shot colour only every 4th pixel has a red lens over it).
7. More accessories. Filter wheels, off axis guiders, adaptive optics units.
8. Large chips are available. Larger than Canon 5D.
It really boils down to cooling. Powerful CCD cooled chips are very low noise.
As far as CCD versus CMOS (DSLRs are CMOS chips) I am not sure of the differences beyond
the fact that as far as I am aware there is more research happening in CMOS as it seems more aligned
with the major markets. Of course Canon makes their own. They often seem to be trying to lower noise
and improve low light performance. Also the electronics are continually becoming more sophisticated.
But for bright objects the difference as above is not as great.
When doing a dim galaxy or dust area or narrowband the difference becomes greater.
Some of the very best DSLR images though I have seen are still from the now outdated 20Da the astronomy version Canon put out once.
I think just about everyone starts with a DSLR. Enjoy them, they are a lot of fun. Eventually though you will want to go that extra
for your images that only a dedicated astronomy CCD can deliver and they are all not the same either. A cheap astro CCD is not as good as a lot of the nice DSLRs these days. So that is another factor. Not all astro CCDs are better than modified and cooled DSLRs.
I'd leave that point for others with one shot colour CCD cameras about which are better than what.
Greg.