I've recently upgraded a NN5 with the 2nd gen. Arca-style quick-release clamp (ASQRC-2). I use a Pentax K20D w/ the battery grip, and a Kirk custom-fit Arca plate. Everything fits together solidly and is very easy to operate, even though the Kirk plate is longer than the clamp by quite a bit.
The problem is that there is no *repeatable* way to insure that my plate is in the clamp at the same place every time unless I use one of the "flip-up" stops included with the clamp (thanks, Nick!). The plate hits this stop and the lens centerline (as seen when shooting the rotator from above) is still about 2mm off, despite adjusting the Kirk plate as much as possible on the grip (which has a tripod mount about 10mm off to begin with). This means my lens centerline is not perfectly in line with the NN5's upper arm and rotator joint, but about 2mm *above* it.
This is a rough place to start the calibration of my body and 10-17mm fisheye on the head. Given that I only ever shoot at 10mm (6 around, +zenith, maybe nadir) and always have the grip on the camera, can this be worked around (or ignored)?
I think the 6 horizon-shots will be fine no matter what "height" the lens is above the rotator, but as soon as I flip for the zenith, the shot is off by 2mm. I've calibrated my pan-head countless times before with other bodies and lenses, but always *started* with the lens perfectly in-line with the upper arm, and with this variance, I don't trust my own (horizontal) calibration. Any insights on how bad this could be?
(BTW, I stitch with Stitcher 2009 and use Smartblend - my few tests (with featureless ceilings and trees outside) show no big problems... yet.)