[Pavel]

Very fast primes tend to be very sharp in the center but the sharpness falls of (often rapidly) off center and in the corners. With D300, I wanted to compose in the field, often placing the visual focus off center, in the area of relative softness. That tended to limit the use of very wide apertures. I did not want to crop too much. With D800, there are so many pixels, that I can afford to place visual focus in the middle, use wide aperture and crop like crazy.

It took me a long time to unlearn placing visual focus in the center. Now I will have to unlearn placing it off center and learn again placing it in the center, at least when I shoot wide open with fast lenses. Never thought of that. Just sharing my thoughts....