[gregbradley]

Thanks Alex for that informative writeup.

My first astro camera was a Nikon D70 and it was very good. Just as a point of interest - the 6.3mp chip in that camera is a Sony and is the same as used in the Starlight express MXx25C and the QHY8. In those days the Nikon had bad amp glow and also did not have true RAW files (unprocessed saved data).

As far as I know (please correct me if I am wrong) that is still true today.
Nikon has its own file format called a NEF file and this has some smoothing run on the image before it is saved. This is done to reduce noise (astroimagers know you sometimes need to smooth areas of noise in the dim areas of an image to get a pleasing result).

This has the effect of reducing smaller. delicate, fine detail in an astro image. Exactly how much is debatable - perhaps not much at all but it is present.

This was and still is one of the major arguments against using a Nikon.

I know up to the Nikon 200D (I think that was its designation) the Canons were clearly superior. However later models I have no knowledge of and Alex does.

Having said all that I believe a QHY8 would be far superior to any DSLR and a smaller SBIG 2nd hand would also be far superior.

Dedicated CCD cameras have the following advantages/disadvantages:

1. High cost - disadvantage although QHY have brought the costs down a lot and are closer to a DSLR with a couple of lenses.
2. Cooled - far lower noise, a major advantage
3. 16bit processing - this means a larger dynamic range although the new DSLRS are 14bit and it could be argued that 16bit is not fully utilised in CCD cameras as the image data is only in a small part of the range it can differentiate in.
4. SBIGs have internal self guiding which means autoguiding is all in one package and you have to add on the cost of a good autoguiding system to a DSLR to compare costs (as a guide I'd say $1000 minimum for a decent autoguiding/guide scope/rings/mounting gear setup and easily could go to $2500 for this alone + the problems of flexure can enter where the guide cam and imaging camera are moving very slightly from each other and you get eggy stars).
5. filtered imaging means each pixel counts when doing LRGB imaging versus a DSLR where it has a coloured grid overlay of microfilters on the chip so 4 pixels are required to create one colour pixel in other words your 10 megapixel chip is only really 2.5 megapixels of colour.
6. Unmodified DSLRs are a lot less sensitive than dedicated mono astro cameras and modified cameras are also although less so. Sensitivity is typically
3 times greater for a cooled dedicated astro camera than a DSLR.
7. If you want to do narrowband imaging (Ha filter for example) it is ideally done with a dedicated astrocamera. You can use Ha with a DSLR but it is less sensitive to this and unmodified it may be a waste of time as the standard Canon/Nikon filter blocks that light. Modified cameras it is not.
8. Dedicated astro CCD needs a laptop and a battery or power supply. DSLR is more portable and does not absolutely require a laptop so this could be a big advantage.
9. DSLRs can be used for other photography - this is often appealling as well. However point and shoot cameras these days do an awesome job and an excellent one costs less than $100 now and they are a lot more portable and fit in your pocket.

So if it comes down to money a one shot colour QHY8 would actually not be much more at all.
A 2nd hand SBIG camera would also not be much more when you consider not needing a separate autoguiding setup (which you will need to do serious imaging).

Results will be much better with the dedicated astro-CCD.

I guess it comes down to how hard are you going to get into this hobby - mildly interested or full on? If full-on you will eventually want the dedicated astro camera so you could just start at that level and save yourself some cost of changing over later.

Greg.