hi. Am looking at these two lenses as a prime for my M1. I've had the 25mm before and liked it (now sold) but wondered about the sigma. By all accounts it's very good and I often shoot longer anyway, plus the extra isolation I would get would be nice - I love close up/detail shots. My only concern is the size/weight. The cost used of the 25 is about the same as a new sigma 30. Any thoughts from sigma owners. Are you happy with it? Any down sides? Thanks.