[gregbradley]

I agree with those assessments from what I have seen of posted images. Full frame is hard to beat. Its a bigger sensor so therefore a bigger light bucket. I have Nikon D800E, Fuji XE1 mirrorless ($815 body only) Sony Nex 6 Mirrorless (same as Fuji body only). The mirrorless are both APSc sensors same size as 60Da, 70D etc etc. Its a Sony Exmor sensor so its got great low light low noise high ISO performance. But not as good as the Nikon. So smaller sensors even if excellent at present do not match current full frame sensors. Fuji is closest though.

There are alternatives of course to those. Nikon D600 is the competitor to 6D. This would match the 6D. It also has internal time lapse and interval shooting options which are great as no need for an external intervalometer to do time lapse should that interest you. Both are the same price. D600 has a dust issue though. Its only fault otherwise universally raved about by owners. So you'd have to clean it regularly with a wet swab.

But mirrorless should be considered. There are cheap accessories available now that may well narrow that gap between mirrorless APSc sensors and full frame and make them more equivalent. Yet to be proven though. I'll be posting about it in the near future as I have ordered one for my Nex 6. I suspect it will make it closer in performance to the full frame cameras and when available for the Fuji XE1 even more likely to be close, all for less money overall.

Costs are lower as well with mirrorless. They work better with Polarie as they are lighter. Lenses are cheaper. You can get plenty of adapters and use older but high quality lenses that are very cheap. For example the older Contax g Zeiss 35mm lenses are just jaw droppingly good. Stunning. Yet a 90mm F2.8 Sonnar costs on ebay about $200. The 45mm F2 (some reviews rate it as one of the sharpest lenses ever) is about $450 same for the 28mm F2.8. Fuji's new lenses are superb, better in general than Sony's. For example there are no other manufacturers who have a lens that can match Fuji's new 14mm F2.8 (except perhaps the new Zeiss 12mm F2.8 touit lens). Its as good or better than my Nikon 14-24mm F2.8. It has zero distortion. Amazing. Perfect for nightscapes,it also has a manual focus lock which I find helpful as its easy to knock a lens off focus at night. Fuji's 35mm F1.4 is often compared to top of the line Leica lenses- it is that good. Fuji is perhaps not as well known as the more common brands like Nikon and Canon but they are winning big time with their new cameras.

There are also youtube videos detailing how to mod a Nex 6 and whilst its a complicated little camera you do not need to replace the low pass filter on it as it has on chip autofocusing. So you can simply remove it. The 5r, again you can simply remove it and the little washers that currently on top go under the sensor board which just happen to be the exact right spacing to restore the sensor to the right distance.

Not sure what the appeal of a large DSLR would be here over a nice mirrorless unless you go full frame (for now). The mirrorless tend to be superior in all ways except fast AF tracking of moving objects. Unless you go full frame. The only mirrorless full frame are Leicas (mega $$).

Mirrorless are likely to be full frame though within a year with a rumoured Sony Nex 9. I think that could be an awesome machine.

I like my Fuji XE1 and Nex 6 and they are particularly great for terrestial (also light) but do not match the full frame power of the Nikon D800E.
Still they are not far away, closer than you would think. I think either would outperform any of the current Canon APSc cameras in low light high ISO and perhaps some of the Nikon APSc (not sure to be honest). The Fuji in particular as it has its own proprietary colour matrix on the sensor. One of the characteristics of that colour array is low luminance noise. It is particularly clean.

There's also Olympus OMD EM5 and a new EP5 model. That is micro 4/3rds and a smaller sensor though so again battling against physics there.

Sony Nex 6 has a time lapse app you can download. I have been using it for a while now. Its great. Its one of the reasons I got a Nex 6. It works much like the internal Nikon one. It took me a while to work out how to use it (not particularly user friendly but once learned it seems easy enough) but its quite a good little system. Battery life on a Nex 6 is good enough to do a 6 hour time lapse which is impressive.

So I would rate either the Sony Nex 5r or 6 and the Fuji XE1 to be excellent nightscape cameras with a good lens. The Fuji has the better lens lineup. XE1 and 14mm F2.8/Polarie and you are good to go.

Greg.