Ps - I really hope Canon resist the temptation to take their 1.6x crop sensor up to 24mp. It'll suffer from softness due to diffraction from f6.0 onwards - mount an f5.6 lens on there and you've got little in the way of options. Even the legendary 300/2.8 II with a 2x TC III will underperform, and leave you with just one aperture option if you want to attempt to utilise all of those megapixels. Leave the MP lower, and let those lower processing overheads allow them to push the hardware of the small mirror and shutter to its limits.
Once again, this rhetoric keeps cropping up and it is completely incorrect! NEVER, in ANY CASE, is more megapixels bad because of diffraction!
That is so frequently quoted, and it is so frequently wrong. To quote myself:
This camera would have a pixel density equal to a 61mp full frame camera, that is far beyond the resolving power of most lenses.
Grrrrr....would people quit saying entirely wrong stuff like that please? First of all resolving power doesn't work like that. Second, even if it did the better lenses can already resolve up into the many hundreds of megapixels on full frame.
Yes, but diffraction softness at this pixel density starts to become a problem, get up to f/5.6 or higher and you start loosing sharpness.
Diffraction is the most misunderstood concept in photography. The notion that diffraction is ever a "problem" is just flat out wrong. Just because diffraction starts earlier with smaller pixels does NOT mean you are resolving less detail. The amount of detail resolved by the lens is fixed, and independent of the sensor. Assuming a 24mp sensor outresolves the lens while an 18mp sensor does not, no matter how you slice it, even when diffraction blur starts, the 24mp is and always will be resolving more detail than the 18mp. If you scale the 24mp sensor image down to 18mp image size without any additional processing, the 24mp will always be sharper (assuming focus, aperture, etc. were all configured identically between the two cameras.)
Diffraction is the fault of the lens, not the sensor...both the 24mp and 18mp sensors are experiencing the exact same amount of softening due to diffraction...it is simply that the 18mp is PHYSICALLY INCAPABLE of actually demonstrating that fact, while the 24mp IS CAPABLE. A 22mp sensor would be somewhat capable of showing you that diffraction, however it would not be as good as the 24mp, and still, no matter how you slice it, the 24mp sensor (all other factors being equal) would STILL be resolving more detail, even if its slightly softer than the 22mp. Even if that additional detail just means the circumference of the blur circle is better defined.
I really have to emphasize this: In no way, ever, can diffraction produce worse results on a higher resolution sensor than a lower resolution sensor. EVER. Even if, at 100% crop, the detail looks a little soft on the higher resolution image, it will in the worst case be just as good as the lower resolution sensor on a size-normal basis, and in the majority case normalizing size will always make the higher resolution image look better than one taken with a lower resolution sensor.
The 7D has frequently been the target of the mythical diffraction softening problem
and the outresolves all lenses possible problem
on internet forums. I never specifically understood why my 7D was soft until I got my hands on some rental EF 300mm f/2.8 L II, 500mm f/2.8 L II, and 600mm f/2.8 L II lenses. I've used the 300 with 1.4x and 2x TC III's, and the 500 with the 1.4x TC III. IS in all cases was stellar, very sharp and clear, with the one exception being a little bit of visible CA with the 300+2x III. Despite the CA, here is an example (full "crop" and 1:1 pixel peeper on the head) of the 7D with the EF 300mm f/2.8 L II + EF 2x TC III. The aperture used was f/9, so diffraction has definitely "set in" and is visible given the 7D's f/6.9 DLA.
The subject, in this case a Juvenile Baird's Sandpiper, comprised only the center 25% of the frame, and the 300 f/2.8 II w/ 2x TC STILL did a superb job resolving a LOT of detail:
Final crop (Center 25% of frame):
100% Zoom (1:1 pixel peeping):
The difference between the 7D with my 100-400mm f/4.5-5.6 L and the Mark II generation telephoto lenses was night and day. It was completely clear to me that the "softness" was purely the ancient lens design (which, at this point, is over a decade for the 100-400), and that Canon's newest generation of lenses thoroughly outperform the 7D's already high-density sensor. In the case of the 100-400mm lens, the softness was not actually due to diffraction...wide open, it was due to optical aberrations, as at f/5.6 an ideal 100-400 should outresolve the sensor. The 100-400mm is just not a super-sharp lens wide open, and it only reaches ideal performance at f/7.1 (at the cost of additional noise and deeper DOF).
I have further examples of the resolving power of Canon's newest Mark II generation of lenses, at least the telephoto lengths. Given my experience with the 500mm @ 700mm with the 1.4x TC, I have no doubt that a 24mp APS-C 7D with any current-generation lens (such as the forthcoming EF 200-400mm, the new EF 70-300mm f/4-5.6 L, or a potential EF 100-400mm f/4-5.6 L replacement for the current 100-400) they will handily resolve enough detail for a 24mp sensor at apertures wider than f/6. A modernized 100-400 at f/5.6 that sports an MTF around 0.9 should be capable of very sharply resolving detail, even on a 24mp APS-C.