Yes, I'll be doing a ruler test, as a well as a side-by-side test with the P30, the Canon 5D and the Nikon D200 in the next week days to try to isolate the problem.
Hi Willem, I take it you've treid out other lenses at the same distances just to be sure it's a problem with the 140mm. This would seem like the easiest way to locate the source of the problem. It still doesn't mean that it's a problem with the lens, it might be your technique working at that distance with a long, heavy lens.
Just a thought, but wouldn't shooting a ruler on and off a tripod at different distances, with different lenses tell you if it's the 140mm or not?