I realize that I'm replying to an old post that's part of an old thread with recent activity due to the high mp alleged confirmation by Canon.
I wanted to address one thing in particular though. I question the assumption that recent lenses and mk ii lenses are being refreshed for higher mp sensors, including current aps-c 18mp crop sensors.
I was wondering earlier how the current EF 70-200mm f/2.8 IS II USM would perform on a higher mp camera, so I tried looking up its resolving power in lp/mm and ran across a review I hadn't read before, by DxOMark stating that for that particular lens its predecessor, the original EF 70-200 f/2.8 IS USM (mk I) had more resolving power. Then in the comments, they stated that it was sharper on aps-c bodies than it is on ff bodies (which I didn't understand). I've not read any other review that made such claims.
Then I decided to look into the new 100-400mm zoom mk II and read that more or less it has about the same resolving power as its predecessor, and the true improvement is in the stabilization upgrade/update. Was it already resolving well enough before? I've never used one, so I don't know.
Any thoughts on this. I am aware that many here are not fans of DxOMark and their results, but the 100-400 II still has me scratching my head.
Well, your relying on DXO. Guess that's enough said.
One thing I will say is, older Canon lenses often resolved very well in the center, and very poorly in the corners. For film, where huge enlargements were not as common (most of the time, it was smaller enlargements or contact prints, so maybe 8x10 tops on average), poorer corners were probably not as much of a problem. Newer Canon lenses and the Mark III TCs have all been addressing corner performance. Some of Canon's newer lenses did not improve center or midframe resolution much...but improved corner resolution a ton. Some lenses, like many of the new Great White Mark II generation, improved resolving power across the board.
For the best lens resolution tests around, check out Roger Cicala's LensRentals blog. He regularly tests new lenses, using an optical test bench (so he's testing LENSES, not camera systems), and his comparisons tend to be more accurate and generic than most. None of this "limited by the sensor" crap that skews and convolutes results.
There's a few other factors to consider here. Most f2.8 zooms are tested in the middle of their zoom range. The mkII's are optimised at their previously weakest point...at the long end or the wide end, depending on which lens. The 70-200 f2.8 LIS II is a lot sharper at 200mm f2.8 then the mkI. But it's slightly softer at 70mm. Stop down to f8 and both lenses are just as sharp as each other. There is little difference.
The 24-70L was optimised for the 70mm end, the new one is better at the 24mm end. Again, stop down a few stops and there is little between them.
On most zoom Lenses, sharpness often changes slightly through the focal range and focus range. Very few test sites take this into account. A lens which is really sharp at one end of the focal range at infinity will have a different sharpness score than one at the other end of the focal range and at Minimum Focus Distance. We are also assuming that every photo is taken on a quality tripod and with perfect focusing.
Photographers often get themselves twisted up over minor sharpness issues, making big purchase decisions over very minor issues. I've been using a 21-22mp sensor since the 5DII (and currently 5DIII) and I've found that it's a really good sensor density for all of my photographic needs. It's an optimum balance between sharpness, resolution, noise, lens resolution burden and file size convenience. I'm really not that fussed about a 40+ mp full frame camera, which is against the tide of a lot of forum thinking.
Photography isn't so much about the kit as it is about a great photograph. Too much attention on the science of photography can pull us away from the the reason we have the kit. Yes the kit helps, the science part...but really it's about the art of the photo not the process or kit. Talk to most great photographers and they rarely talk about kit or technique.