I'm completely having a mental meltdown over which of these two lenses to pick. I rented the 15mm Voigtlander through LensRentals for my Hawaii trip, and got some great pictures with it -- which I mostly don't have online. Here is one. However, part of me wants the 12mm. Advantages of the 15mm: * Cheaper ($549 vs. $849) * Faster (4.5 vs. 5.6) * Lighter (Gandy's site doesn't specify the difference, but the 15mm is a decidedly small lens) * I already have the filter for the 15mm. On the other hand, if you need those things that are 12, 13, 14mm and not within 15mm, you're never going to get it with a 15mm lens. Grebeman has done some compelling photos with the 12mm. So, I can't decide. Part of me thinks I'd be happier overall with the 15mm, but a part of me would always regret not going for the 12mm. The increased size of the 12mm might keep me from carrying it around. You can see the photos here; the 15mm is the left front lens; the 12mm is the left rear lens. I own the 28mm that's immediately to the 12mm's right. (As my two cameras have crop factors of 1.33 and 2, respectively, the lens would be really be 16/24mm vs. 20/30mm.) FWIW, current lens sizes: 28mm C/V Ultron f/1.9, 50mm Summarit f/2, 135mm Hektor f/4.5. I plan to pick up something ultra-wide and fill in a few gaps, probably 40mm and 75mm.