Improvements in Nikon’s autofocusing system in the D6 include enhancements to the 3D Auto Focus Feature. It allows the shooter to select the starting point for the autofocus which so far to me seems like a great feature. I tried it out in my backyard when the adorable Bushtits were heading down to the fountain for a bath. They congregate on the leafy twigs and branches behind the fountain as they make their way to the water. The 3D system picked out this Bushtit in the midst of lots of leaves because I had the starting point just to the left and slightly up of center. So far I am pleased with how quickly it reacts and maintains focus once it latches on. Nikon D6, Nikkor 500mm PF.