I've just bought a MR-14 EX II ring flash and the necessary ring adapter for my 100mm 2.8L macro lens. I'm now wondering if there is any reason why I shouldn't leave the adapter on my lens permanently - it seems more practical to just leave it there.
I guess I'll need a new lens cap (I've just tested this - a 58mm cap fits perfectly). I'm not using any other filters, and mounting/dismounting the hood isn't affected by the ring adapter.
Or would I run into vignetting problems in some situations? (I've taken a few test snapshots at f2.8/focus at infinity, and I can't really tell if there's a difference, so that should mean it's OK, right?)