I have one of these:
http://www.kirkphoto.com/supports.html#rail
this let's me rotate the QR plate depending on if I'm mounting the camera plate or a lens collar plate to the rail.
Having said that, the 100-400 is long enough that foreground parallax hasn't been a problem for me (ie rotating over the collar attachment point is fine), but if you wanted to move the point of rotation back farther this would work.
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You understand the issue perfectly, and that rail solves the problem. What do you need to do to rotate the clamp? Is it an allen screw, or is it more readily adjusted in the field with a thumb-screw or something. I use a [a href=\"http://www.reallyrightstuff.com/rrs/Itemdesc.asp?ic=MPR%2D192&eq=&Tp=]RRS MPR 192[/url] with a
B2-FAB mounted to it. To rotate the clamp 90 degrees I would need to unscrew the mount with an allen wrench. Not impossible, but definitely a nuisance. Does the kirk stuff work well with RRS? I have heard some mention from RRS that it may not be a perfect match. $125 was a bit more than I had hoped to pay to solve this little problem. Oh well.
While I understand that panoramics taken at the limit of the 400mm range will have minimal parallax error, I like to shoot panoramics with some foreground, or even in macro, so I need to be well calibrated. This means, of course, that I will need to mount it with some precision.
Basically, I use this setup:
Omni-Pivot Package What a lot of people are missing is that if I were to mount the lens with the standard rail orientation in that clamp, the camera would be facing directly up into the sky. Rotating around the lens collar will not put the camera in the right orientation to use the spherical panoramic head to look toward the horizon.