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The Nikon Median filter issue was solved a while ago. I communicated with the engineer who is into astrophotography who worked with Nikon to handle it. It was the hot pixel suppression algorithim that was being applied to RAWs. It was too strong and its now been made much more sohisticated. I did not notice fine stars being eliminated by the camera when I used a Nikon D800e. Slight amp glow though which made long exposure noise reduction a good choice. It was a slight magenta cast around the bottom and sides. Not strong but there.
I think most modern cameras have advanced a great deal on low light high ISO performance which is what you need. In nutshell what you need is a camera capable of reasonably low noise in a 30 second ISO6400 shot on a summer's night. That narrows the field quite bit. Some will do ISO3200. Add to this the fact that ISO6400 is not equal across manufacturers and it becomes harder to evaluate. Fuji's ISO6400 is more like Nikons ISO4000. Sony's ISO6400 is more like Nikon's ISO8000 (if there were one). Nikon and Canon though seem to similar.
As far as I know the current market the best cameras for widefield nightscapes are:
Full Frame not in order of what is best:
1. Canon 6D, 1Dx, 5D3.
2. Nikon D4, D800, D800e, D600, D610 the new Nikon DF.
3. Sony A7, A7r
APSc:
1. Fuji XE1, XE2, XPro 1, XM1.
2. Sony Nex 3, 5 and 6 perhaps 7.
3. Canon and Nikon competing models.
Micro four thirds:
1. Olympus OMD EM1 and EM5.
Probably others but I am not that familiar with M43 cameras.
I would rate the Canon 6D and Sony A7r/Nikon D800e/D4/DF as the best of the full frames. I did a same shot, same tripod, same settings but different lens - I can post results, it was a superlative Zeiss 21mm F2.8 though on a 5D3 head to head to with A7r at my dark site.The Sony picked up lots of airglow and beautiful colour and noticeably brighter image whereas the Canon showed none or little and had a brown hue to everything. I was a bit surprised at the relatively poor Canon shot which I would not have been happy with. I started processing the Canon shot so there may be more in it that can be brought out. There are plenty of great 6D shots though. Never tried one but it seems to be the one. Nikon D800e was a tad cleaner than the Sony A7r but the noise is easily controlled. I think the Sony and Nikon engineers have set up the same sensor in different ways so the results aren't identical. Sony ISO6400 seems brighter than Nikon's ISO6400, plus Nikon seems to have taken a lower noise less microcontrast approach over Sony who seems to have gone for max detail and contrast and a tad more noise and a RAW which has some sort of noise suppression going on. I am not sure any maker makes a camera where RAW = untouched RAW anymore.
The Nikon DF is most likely the king of low noise night imaging as its the same sensor as the Nikon D4 only tweaked even a touch better.
In APSc world I think the choice is easier. Apart from computer control (you can wifi remote control XE2) Fuji is still the class leader as far as I am aware. Most Canon APSc seem very noisy. Not sure about the Nikons. Probably a lot cleaner. Different models use different manufacturers sensors. D7100 for example is a Toshiba whereas anything 16mp would be a Sony.Also amp glow would need to be tested for. There is an astro digital camera Yahoo site. I am sure there would be lots who could answer with direct experience.
Also consider the lens. Its really important in the system. The 2 best ultrawide angle lenses out there are the Nikon 14-24mm F2.8ED ($1700 lens) and the Fuji 14mm F2.8 lens (about $800). Both are sensational lenses and the Fuji has a small section top left and right - about 5% of the image which is not fully corrected, has zero distortion, is sharp, has a lockable manual focus ring, is metal, has an aperture ring. Nikon 14-24 is large, heavy and expensive but really none better. Nikon 18-35 is a possible lens to check but never used it. Reviews are hot though.
Samyang 14mm is popular but has moustache distortion. Getting a good ultra wide can be frustrating so consider this point. Most UWA have poor side and corner performance.
One of the best astro cameras I think is a modded Canon 5D2. That produces stunning images. They are down to about $1000 sometimes these days.
Sony A7r is the smallest and lightest full frame and is 36.4mp (same sensor as D800E) but no AA filter (as opposed to 2 selfcancelling AA filters). There is an A7 which is about $1500 which is 24mp (same as Nikon D610) which makes it the cheapest full frame camera on the market although 6D is about $1800 or a bit less. A Vixen Polarie will load above its stated weight limit but the A7 would be one of the few cameras within the stated limit. Not that relevant really considering the Polarie will handle a Nikon D800e and heavy 14-24 lens once the tightening screws are tightened hard.
As you can see I am now a fan of the Sony but really a 6D, Nikon full frame or Sony would be a fabulous camera and Fuji X series also fabulous.
As far as Canon/Nikon APSc not so sure. Canon got involved like everyone else, in the megapixel race so 18-24mp for an APSc sensor does not sound like a good formula for low noise high ISO performance (small pixels = more noise usually).
DPreview.com has a studio tool where you can compare the various camera models ISO performance side by side. I would start there. It won't show amp glow though.
One last consideration. Some Nikon models have a built in time lapse function and intervalometer which is very nice. Sony has it as an app you buy and install on Nex 5, 6, A7 A7r cameras which is very similar to the Nikon (a bit harder to work out but works the same way).
My 2C.
Greg.
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