80mm apo or 200mm newt for deep sky?

[Beardy Bob]

I know this is an historically contentious issue, but I'm going to ask anyway because I need help to make a decision! I currently use a c80ed and DSLR with a guide scope for imaging deep sky stuff, but the mount could take a 200mm reflector (I could only afford a 'normal' one, not a fancy newt-cross astrograph or anything) with an off-axis guider, which would also allow me to do some planetary imaging.

My question is whether the larger aperture of the reflector would give me any greater resolution for deep-sky images, or whether this is only true of planetary imaging with sub-second exposure times?

[nmoushon]

Aperture is kind of a touchy subject so here's my take on it. For DSO imaging aperture does increase resolution but it would not be very noticeable at the amateur scale. This is also debatable if using CCD cameras but since you're using DSLR, as am I, I think its not very noticeable because of the amount of noise you get with the DSLR. You're images will seem to get more resolution but that is mainly from the increase in focal length and thus the details of the object are larger and can be brought out more. When it comes to planetary imaging the aperture will indeed increase the resolution along with the scale because of the increase in focal length. But keep in mind the its better to planetary image with AVI vs DSLR so a new camera would be in order.

[Beardy Bob]

Thanks. That is the general impression I got given what scopes people use for deep sky stuff (colour-corrected, small refractors). I had also read recently on here that changes in the atmosphere during a long exposure will make the finer details elusive regardless of aperture, which again makes sense. But recently I have seen some fantastic deep sky images taken with very large aperture newt-type scopes and wasn't sure whether people used them just to lower exposure times or whether they brought an improvement in image quality over a small apo too.

Oh, and the camera for planetary imaging would be no problem. I can just use my QHY5 guide camera!