K said:
IF ...giving up mexapixels leads to improved DR / ISO performance - I would take that trade off in a 5D series camera with limits though.
I would want the lower end to be about 20.2MP. This is judging by my 6D that produces incredible detail of which I rarely find any use for more. I'd rather have a 20.2 low light beast than a 28-36MP sensor that gives up a little ISO/DR for a little bit more res.
Folks, we now have the 5DS line. If you need insane detail or cropping ability - there's your camera. With 20MP, I only miss the extra megapixels a tiny percentage of the time (maybe 1 in 800 keepers for an event) when I find a nice composition within a scene and it is a real deep crop where too much detail is lost. Almost all the time, I can go in pretty far and still end up with enough detail to make perfect photobook sized prints. It is rare to the point of being pointless to worry about.
What we need now is for Canon to again become the leader in low-light. Some more DR would be welcomed too. But not as important as the Exmorites make it out to be. I'm not in the business of underexposing everything by shooting at ISO 100 or 200 then doing 5-7 stop lifts.
Unfortunately, practicality does not rule the day. Marketing dictates that Canon must up the pixel count. Even if it is a small amount, it must be more - or else they will face the wrath of all the blogosphere and web reviewers out there. Especially the specs-driven COMPUTER and electronics review and info sites. These sites all comment and do light weight summary reviews on all camera bodies, and they are not photo experts. They simply focus on published specs the same way they do for computer hardware. These big name sites reach a LOT of viewers and readers.
For this reason alone, the MP count will go up, never down.
Since megapixels are going up - there's no point whatsoever in having a low MP, super high ISO camera. I strongly doubt Canon is going to follow what Sony did.
This is a general question - for anyone to answer, and I genuinely would love to know - but related to what you say. With each generation of cameras, MP counts go up, low light performance also improves. So in principle, more MP does not mean worse low light performance, right? Either they are not linked the way some people think, or else other improvements are made that offset any problems. So why do people keep assuming that the only way for future cameras to improve low light performance is to reduce MP counts, or at least keep them where they are now?
The A7s is an interesting camera, but do we know for sure that its high ISO capabilities are actually down to the MP count, or is something else going on here?