I am setting up my 'blad 203 FE with a Mutar 1.4 in order to do horizontal stitching. It is my rather fuzzy understanding that if the lens is the moving component used to create the "stitch" then parallax can occur. (If the lens is stationary and the back moves, ie. 'blad Flexbody, then parallax isn't an issue?) If my camera is mounted on a rail and I move the rail in an equal and opposite direction to the lens movement then "no parallax"? Or am I totally confuses. :>)
There are 2 possibilities.
1. You use a horizontal rail from left to right, and offset the lateral shift of the lens' entrance pupil caused by rotating at an axis that's too far back. Drawback is that the lateral offset is different for each different amount of rotation.
2. You use a fore/aft rail and slide the camera back until the rotation axis coincides with the entrance pupil. This is the preferred approach because the amount of rotation becomes unimportant. The only thing to watch out for is with close-up photography where the focusing itself may cause a fore/aft shift of the entrance pupil.
For scenarios without any near foreground detail, and a liberal amount of overlap, one can sometimes skip the no-parallax preventative cure. However, doing it the correct way has it's benefits (reducing the srew-up potential usually does...).