[Shiraz (Ray)]

Hi Alastair

I was referring to Clive's 3200, not a brand new one, when comparing options. Looks like NABG can be managed - for example, John Hothersal has published some images from his 3200 with no obvious signs of blooming.

The dynamic range of the 8300 is slightly less than that of the 694. The QE is significantly lower and it is noisier. RBI can apparently be an issue if it is cooled too heavily. All this really means is that you need to spend a significantly longer time getting image data with an 8300 - you will certainly be able to produce good images with one and the pixel size is a good match to your scope.

As far as I can tell, the RCC1 does not introduce any SA, but it will add significant vignetting with anything much larger than the 694. I tested it with my QHY8 and it was just usable. Paracorr might be worth looking at for an 8300, although that will rule out AO due to limited back focus.

Not sure about AO on any chip at f4 - it's a lot to squeeze in. And there is the possibility of spherical aberration from a refractive AO (not from a reflective one though).

Agree with Peter re the secondary - I needed a 70mm in my 200f4 and would expect that you will need something above 80mm.