At least we are getting a presumably fairly solid rumour here? .... I have been waiting since before the 5D mkIII for the next generation of sensors, that Nikon / Sony must of had in development 4 years ago. So what have Canon been doing? And I'm quite dismayed about this.
For me its not all about MP, I think 50mp on 35mm might be too much.. for most people and pushing sensor density and lens to limits. I think 40MP with 2 stops more DR and the most important NO banding / noise in shadows at 100-400 would be the optimum combination.
I shoot studio work at lot and this would make a huge difference when dealing with low key subjects plus simply having a more maluable file to push and retouch with. I did a head to head test with my friends D800 the other day as was seriously considering getting one to run alongside my 5D mkIII.
So I hope this is of interest and not too off topic, but for those debating the D800 vs 5D mkIII or MFDB or wanting more MP read on. And when I get time this week I will post a proper review of my tests with samples.
The first thing I found was the D800 has not much more DR in a studio setting with a subject full of smooth tones and some fairly contrasty areas. The D800 is a more natural looking file and much less micro contrast & sharpness compared to canon raws straight out of the box. The actual MP size difference was not that big, nothing that couldnt successfully be upscaled. But the shadow detail had quite a bit less noise, but also had less information in it, it seemed the noise in the canons shadow areas was actually emphasising any subtle details especially on skin texture.
As some other posters correctly said its about what you do with the file and how you shoot to capture the exposure.
In canons case overexpose TTR and get a cleaner file plus you can pull back the highlights slightly more than the D800.
But if you do underexpose or have to pull shadow up a lot then the D800 wins hands down.
Surprisingly in my tests I compared my experience of Hasselblad H3DII-39 and Phase one P30+ image quality and the D800 is better than the Hasselblad sensor -cleaner and can be pushed more, although it is not as bitingly sharp but that can easily be added later. And the P30 is a harder more processed looking file similar to the canon but can be pushed a lot but is also very smooth at the same time.
But what I did find was the most important factor - LENS, I only had access to the nikon 24-70 and tested it against the canon 24-105 L and 50mm 1.4 and both the canon lens appeared to be sharper. I believe 50 % was due to sharper lens and 50% due to the way the canon raw files are sharper to begin with before any sharpening can be applied in processing. Also because of the slightly smaller file size the canon images looked sharper overall which is good news for most uses up to 24" prints I would imagine.
Then the next day I tested out the 35L , 50L and 85L and I was very surprised by the look from these lens, not quite enough is written about this in reviews that concentrate on sharpness , CA, vignetting and bokeh. Bokeh is one thing but the way these lenses smoothly draw the image and combined with the punchy raw characteristics the camera it was amazingly similar to the Hasselblad primes with a Phase One back which is very impressive indeed.
So after a lot of studying files and forums about the D800 then testing it myself I ended up with the surprise conclusion to invest more into Canon-specifically the main 3 primes I don't have yet, 35L (though may try the sigma as well) 50L and 85L as this will have the nicest and biggest impact on the look and feel of my images.
And beyond that i really do hope canon do produce a sensor with as clean shadows as the D800 in the next year or I will be really sad to have to look to alternatives again.
However I am slightly scared that they will produce a monster MP 50+ with less than 1 stop better DR and more noise reduction to keep shadow noise at bay rather than concentrating on a purely better sensor in terms of DR, tonal gradation and shadow noise/ banding.
One last word is please people and Canon stop this hi-iso driven quest, very rarely do most people need to shoot over 6400 and how many truly beautiful images have been made at stupidly high ISOs. It's ruining photography for a lot I believe compared to few good snaps you might be able to get and marvel about how dark it was!
When I saw a post recently about them demoing a video sensor that can shoot in near darkness I wailled and cursed why are their R&D so obsessed with that and video .. remember proper photographers that like to use light, studio flash and shoot mostly at 100iso for beautiful clean stunning professional results!