Thanks for chiming in on this everyone. I'm sure the answer is simple but it's not clicking.
I have been shooting with a square-format MF back on a Contax 645. With the giant 350 lens mounted, I've used either a tripod or more commonly, a monopod, supporting the lens by its foot. (the foot has a RRS QR plate on it; the monopod, a basic RRS clamp.) Obviously, switching from landscape to portrait mode is not an issue with square format.
With rectangular-format cameras, how is this best accomplished? How do you easily move between portrait and landscape orientation with the lens foot mounted to the monopod? I have a swivel for the monopod, but flipping it up (to allow portrait orientation) is cumbersome, and then the weight of the lens does not fall along the axis of the monopod. It seems very unstable. I'm unfamiliar with Nikon/Canon lens collars--does one merely loosen the collar nut and rotate the lens within its collar?
Question arises as I have some new Nikon gear en route. Thanks everyone.
Mike