I got a NN 3 mk2 and use a 5D2.
I saw one where they tilted the camera and I think they used a 8 mm and that way got the zenith too.
You can with the 8mm on a cropped sensor body.
But not with the 15mm Canon Fisheye on fullframe body like the 5D2.
And using an 8mm fisheye on a fullframe sensor body 'wastes' a lot of sensor area.
My reason for the change is that it would be nice with a smaller black whole in nadir, quick setup and being able to leave the lens and use the camera with another lens.
You should be able to use a shooting pattern with your 5D2/15mm FE that gives small nadir hole.
What pattern do you shoot?
Remember the R1/R10 are single row heads - so no use for shooting 360x180 with your camera/lens combo.
You could look at using a RS-1 or RS-2:http://shop.nodalninja.com/custom-heads-rs-1/2
Or consider converting your NN3 with an RS-1 adapter/convertor:http://shop.nodalninja.com/rs-1-upper-r ... embly-kit/
Or look at a QR mounting for your NN3, if it will fit along with the 5D2.http://shop.nodalninja.com/clamps/
The Ultimate R 10 from NN and the Atome from 360precision is used by googles trusted photographers to take pics from shops.
Yes, I have an R10 which I use with a Nikon DX body and Sigma 8mm fisheye.