The good news is that I got a solution regarding AF from Leica that enables the Sigma 100-400mm to perform at its best. Illogical as the solution sounded, it worked. The camera didn’t miss in very poor light in a brief outing late this afternoon.
The bad news is that the zoom is still not good. Worse, the zoom with teleconverter is not much better. All three of the plastic Canon lenses, the two DO, and the lightweight zoom, absolutely bury the Sigma with their performance. And that’s shooting on Canon’s tiny crop sensor while the Sigma is on a full frame body!!
The combo will get one more try in good light (if there’s ever any), and the zoom will eventually get trundled off unless a miracle occurs. The teleconverter will likely be retained in case a decent lens comes along to pair it with, even if it’s Lumix. I’ve long suspected that the Lumix TC’s are Sigma-made anyway, as they are same weight, same dimensions, and same optics—and made in Japan.
How bad is it? Well, some fine print on a distant signboard that the R180 + 2X at 358mm can just barely resolve to legibility appears as a blank white spot when shot with the 560mm Sigma combo!! The first, DSLR version of this lens I owned was far better optically than the current one is.
Five-digit ISO didn’t help matters, but then bright sunshine probably wouldn’t have, either!