[JensE]

That setup won't work because the rotation axis is behind the camera.

Re-read the description ...

My minimalist setup consists of a single long rail and spare ball head mounted on it. Gets me close enough, within a few millimeters.

[biz-engineer]

Re-read the description ...

Apologize. Done, and edited

[JensE]

My makeshift setup, rail and head normally used in conjunction with my macro rail, so I didn't have to buy anything. (Heads normally used switched, just testing the lighter one on my tripod for general use.)

The lens-dependent position of the ballhead is marked on the underside of the plate, the plate edge is mounted flush to the quick release clamp. The remaining adjustable degree of freedom is the 'panning' angle of the head on the plate. Not a problem with the fish-eye, because the entrance pupil is basically at the very front of the lens and thus easy to align well enough with the plate. For other lenses, I plan to mount the upper head at a fixed angle on the long plate and note down the pano scale angle of the upper head - once I get to it.

An interesting option with this setup is to use it with the camera slanted diagonally, so that the entire sphere can be covered with the fish-eye and horizontal rotation only.

The two pieces (plate and small head) are easy to pack on hikes, something I would likely not do with a gimbal - which I'll give try nevertheless.

Note that this setup has one 'missing' degree of freedom around the nodal point: tilting the camera up for multi-row panos. I haven't done any multi-row panos, and with the excellent fish-eye, I don't expect to ever need to. A clamp plus L-bracket would work instead of the ball head for vertical orientation, but you'd lose the slant option.

[Arjay Bee]

This solution has a bit of vibration in it but works with a cable remote and mirror lockup with 2 second delay - uses a 4way focussing rail and a L bracket. Short lenses are best to prevent the droop others describe.

[swanlefitte]

I have used my sigma 10-20 but I found my sigma 18-35 much better for stitching because distortion matters.