Fisheye for D800?

I'll respectfully disagree with some of the above.  I have the 10.5 DX and a D800, and I think it's a fine fit.  The 10.5 is one of the real bargains from Nikon, it is a very sharp and well built lens (admittedly with screw focus).  It focuses from almost touching the lens (half the distance of the 16mm), and yields good color and contrast.  It's auto-focus unlike the 16mm.

Auto-focus is arguably less important on a fisheye, but one use I love for it is to just hold it up overhead in a party or group of people and start shooting different angles.  Nice to have it focusing.

That it is (somewhat) limited to DX is not much of an issue on the D800.   The DX frame will give you still an image comparable to most DX cameras, and it seems unlikely you need a full 36mpx for a fisheye image.

You can (but may not want to) cut the shade off and use it in FX mode and get even a larger field of view.  Here's a site describing it.

http://www.hasselweems.com/photographers/fisheye/index.html

These are on a D300 as I'm on the road and these were online, but that's what DX will be on a D800 (except a few more pixels and a lot more DR):

Camera resting on a railing, long exposure of merry-go-round, 10.5/2.8

You can also defish it and get somewhat interesting rectilinear shots:

10.5 fisheye de-fished with Lightroom

I've replaced almost all my DX lenses with FX for my D800.  But this one I have no urge to change, it's a dynamite little lens on the D800.  If I was shooting solely a smaller FX (e.g. the D4) I might reconsider, but not the D800.