I've been pleasantly surprised by the AF system on the D600. It's very good. I've found it accurately picks up subjects in some very difficult situations. Most recently it was on a trip to Cades Cove in the Great Smoky Mountains.
Here are a couple of images.
This image was taken using the Nikon 200-400 lens. The buck crossed the road behind me and I had to quickly get out and shoot. The camera did a great job of keeping focus on the buck as he was jumping the fence. ISO 1600, 1/400 sec, f/5
This one is of a first year deer - probably about 6-7 months old. Again - its with the 200-400. The deer was with a group of does that were easier to photograph, but I liked the innocence of the fawn. The challenge was picking up focus in a very cluttered scene. There was lots of brush behind the deer, and even when it was in a clearing there were grasses in the focus area. The camera correctly picked up focus on the subject. Camera settings reflected the low light conditions - ISO 400, 1/125 sec, f/4
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#1. "RE: D600 AF - Deer in Cades Cove" | In response to Reply # 0