After seeing some wonderful pictures the last few weeks here from folks with various scopes with longer FL but using the 1600mm I was trying to figure out how pixel size resolution and focal length all go together(Since I am looking to get a bigger scope and reuse my camera and mount to gain resolution.)
Bracken had a great write up in his book hopefully I get this right;
Typical good seeing is for most of us is 2 arc-sec so Nyquist say we want to sample at 2x of what we are trying to reconstruct so we will use 1 arc-sec for sampling. Any combo of focal length and sensor pixel size larger is over sampled and you lose resolution, anything smaller is under-sampled and is fine up to 1/2 of the sampling number based on seeing.
So we want our image scale to be .5-1 arc-sec . Smaller than .5 arc-sec you just don't get the benefits of the larger focal length but it doesn't hurt you.
Using the formula Image Scale=(206.265*pixel size)/Focal Length will tell if we are over sampled, in the .5-1 arc-sec range or need larger pixels to see the full benefit of the larger scope.
Using the ZWO 1600mm at 3.8um pixel size 206.265*3.8= 783 so for any focal length smaller than 783, I am over-sampled and losing details.
Calculating my current SV80ST(480MM F/6) with .8 reducer(384MM) 783/384= 2.04. So this means I am way oversampled and losing significant resolution!(if my seeing gets to 2 arc sec) I wasn't aware until I just did this!
the 8" edge HD is native 2125 MM FL so that gives me a .368 under-sample so I wont get the full benefit unless I get a camera with bigger pixels
the 8" edge HD with .7 reducer is 1487 MM FL so that gives me a .52 under-sample so that's a sweet spot. The question is what do I gain or lose imaging at native focal length VS reducer( I know ill need more time due to F/10 Vs F/7 and guiding will be harder. But do I lose any detail or magnification with my current ZWO?)
the 8" edge HD with hyperstar=390 MM FL so that gives me 2.04. So this means I am way oversampled again.
So to sum it up if I go native 8 edgeHD I'll need bigger pixels to get full benefits, use the .7 reducer I'm in a sweet spot, and hyperstar gets me back to what my stellarvue is capable of due to the oversampling. So I would need two more cameras to get full benefits of the longer EdgeHD, my stellarvue or using hyperstar.
I think I understand this now but please correct if I've overlooked something. This at least give me a range of scopes to look for but the Edge HD seems to fit the bill. I am trying to stay in the 2-3k range with reducers and focuser here so any other suggestions on imaging platforms are welcome. I've read a lot of posts on the RC's and seems like a lot of collimation issues with the cheaper ones that I'm not sure I want to deal with that. Looking into imaging refractors as well as I'm not sure the hyperstar adds much to what I am getting with the Stellarvue already other than less integration time due to F/2(I'm at F/4.8 with the ST80 and reducer)