I recently purchased a mint condition E-M5 + 17mm 1.8. Lots of things I like about that combination. I have been considering buying a 12mm lens for those times I want a wider perspective and can't take a few steps backward. I've viewed many samples from the MFT 12mm options, and all have a lot to offer. The rundown as I see it: 12-40 Pro - great IQ, but large, heavy, and expensive. Weather sealing a plus. 12mm f/2 - small, excellent build, great IQ, snap focus a plus, very expensive, no weather sealing. Rokinon 12mm f/2 - great IQ, no weather sealing, much heavier than the Olympus 12mm f/2 but less than 1/2 the cost. Olympus 12-50 - great IQ from what I have seen, although slower. Excellent macro mode, weather sealed, very reasonable cost if bought used, considerably longer than either 12mm f/2, but very lightweight for its size. I've not looked into any of the Panasonic options. I'm hesitant on the zooms, because I've owned several of the ZD HG zooms in the past, and while their IQ was excellent, I just didn't get along with their size and weight. On the other hand, numerous people say the 12-50 is much better than some reviews have claimed. I'm thinking I'm going to start by renting a 12-50 for evaluation. Anyone else have any thoughts/experiences to share on those lenses?