All of the above cameras have clean HDMI out, which makes use with a Ninja (Prores HQ @220 mbps) a very big advantage over the internal codecs. I will not go into the details of my comparative tests other than to say that I'm only interested in optimum video image quality under normal circumstances...so noise at very high ISO is irrelevant for my selection criteria. I normally shoot at 400 ISO and rarely above 1000 ISO.
To get to the point...for my requirements the Nikon D5200 (with and without the Ninja) produced the best video image in my topside tests. Slightly better than the D800; significantly better than the hacked GH2 and GH3 (which really isn't that different to the GH2's video quality...a bit disappointing, actually).
In terms of DR, color purity, color gradation, color banding (lack of it), moire and aliasing, and...particularly NOISE, the D5200 was significantly better than the GH2/GH3, and somewhat better than the D800. The new Toshiba sensor in the D5200 with the way the processor handles the 24 mp image results in what is to my eyes a very beautiful, neutral and very clean video image. Two other important features of the D5200 (for me, anyway) is decent autofocus (AF-F) during video which is almost as good as Panasonics; and that the HDMI also carries audio...important for topside work with the Ninja. Unlike the D800 it is also possible to have very accurate auto exposure (AE-S) during Live-view video acquisition with the D5200 (and still control shutter preference and ISO).
Of course each camera has its feature advantages (the 50/60p of the GH3 is excellent, whereas the 50/60i of the D5200 is retarded). For still photographers the RAWs out of the D5200 are way better than anything out of the GH3.
If you are wondering why there are no Canon DSLRs on my short list...three reasons: 1) Canon have decided not to allow clean HDMI out for cynical marketing reasons (the HDMI out will soon be miraculously "unlocked" in the Canon 5D3 by a simple firmware update...no doubt in response to the success of the D800); 2) Canons (including the 5D3) have relatively soft video; and 3) I dislike the "Pink Disease" color cast of current Canon lenses. I had a 5D2 with several L lenses for a year...but went back to Nikon and Zeiss glass.
Please regard this as just my personal opinion and a heads up about the cheap and humble D5200. I'm happy to answer questions...but I have neither the time nor desire to post examples to "prove" anything. There's pleanty out there already:
GH2 vs GH3
"If you’re looking for a big leap in video performance over the GH2, the GH3 doesn’t appear to be it."
D5200 vs GH2
This has a couple of frame grabs that clearly shows the noise difference...which is much more noticeable when comparing the video material.
I hope someone makes a good housing for the D5200 asap...or it's another Subal conversion job for me.
Edited by HDVdiver, 14 February 2013 - 04:41 AM.