Nikon and Canon 500mm are so similar they could be regarding a real MTF test . The distance that DXO uses when they measuring up cameras and lenses plays an important role when these lenses are optimized at a certain distance.
I see. Can you point me to some data showing that Nikon and Canon 500mm f/4 lenses are optimized for different
distances, or that DxO tested them at different distances? Or perhaps some other explanation for why the Nikon lens shows a disproportionally much greater IQ decrement compared to the Canon lens?
I stand by my earlier statement - the increased MP count of the D800 over the 5DIII does not offer a benefit commensurate with what the numbers would suggest. To realize something close to that full benefit, you must:
- Pick the right lens. Note that the correct choices don't include such lenses as the 14-24/2.8, 24-70/2.8 (popular pro/wedding lens), or the supertele lenses.
- Use a tripod and MLU (always fun with Nikon's poor implementation of Live View), or have enough light for at least ~1/(~4 x focal length) shutter speed without needing to raise the ISO too high (or kiss the DR benefit goodbye)
- Apparently (according to your post), know the subject distance for which your lens is optimized, and shoot only at that distance (if you know it - where is that specified, exactly?)
Choosing wrong on #1 means you might just end up with lower resolution than with a 5DIII and comparable Canon lens. Failing to apply #2 will give you motion-blurred toss-away images (Canon users who upgraded from the 40D to the 7D learned that lesson the hard way, many thought their old 40D was sharper). I'm still not sure that #3 can even be met, it's hard to always shoot at the optimal distance for your lens without knowing that distance.
It's amusing when people take some aspects of DxOMark's information at face value, but come up with complex, often undocumented reasons to explain how the information that doesn't fit their expectations isn't applicable; or when people link to Scores that don't mean what the poster thinks they mean, and ignore being called on it.