The Nikon D800 is a great camera for video. At least in a studio setup. One of the reasons is the ability to output uncompressed 10 bit video via HDMI. Just add a Blackmagic Intensity to your system and you're good to go.
Having uncompressed video that can be captured as Apple ProRes422 is fantastic for keying. And the better your key to begin with, the less work in post.
Setup is fairly straightforward, the D800 outputs video via HDMI without any on-screen-menu in exactly the same format you chose for recording. Except... it does not.
Here's the catch: When you choose "1920x1080 30P", it's really an "1920x1080 29.97P" output.
When you KNOW this, all is good. If not, you'll be swaping cables, rebooting your system several times and scratching your head why the hell you don't get a picture with the Intensity.
That said, select "1920x1080 29.97P" on the Intensity as input-format and have fun!