Its been two years since Nikons medium-format D800 and D800E SLRs hit the scene, and thats just about an eternity for gadget nerds. What exactly has Nikon been doing since then? Well, aside from working on top-tier beauties like the D4 and D4S, its also been working on a proper successor to the D800 line. Surprise, surprise: its called the D810, and its about the sort of leap forward youd expect from a modest model number jump.