I thought that it's more to do with pixels on target than pixel density.
If you take a d7000 with an 85mm lens and a d800 with a 135mm lens.. They'll have close to the same field of view. The d800 will have 36 million pixels on target and the d700 will have 16 million. If they were both 16mp.. They would have the same motion blur.
In reality.. the d800 has more than twice as much blur at the pixel level. Probably why the d800 promo has it in the introduction and the d7000 does not.
I was using the D7000 as an argument for diffraction, not motion blur.
Motion blur will be the same for any given field of view on any camera. Just that, on a low-resolution sensor, you may only see one pixel of blur (because the distance of blur only covers one pixel) while, on a high-resolution sensor, you may see three or four pixels of blur. Essentially, the single pixel of blur you see on a low-resolution sensor now covers three or four pixels on the high-resolution sensor.
But you still don't get any loss of quality - sure, you'll see more blur on a pixel level, but a 100% crop of a 36MP sensor represents a much higher magnification than a 100% crop on a 12MP sensor. Shrink the 36MP image down to 12MP and the motion blur will appear the same. It's the same thing with noise, really - you may see more noise per pixel in a 36MP sensor, but shrink it down to 12MP and it will look better than the native 12MP sensor.
And, of course, if you shoot with a tripod, or have some other way of mitigating motion blur, the 36MP sensor will give you much more detail than the 12MP sensor.
Switching now



