I find snap focus somewhat problematic in really low light just because there's not a lot of DOF with the lens wide open, so you really have to guess right on distance, whereas in decent light you've got plenty of DOF and margin for error. I did fine with snap focus in some limited but not too bad indoor lighting but when it gets really dark, I use auto focus and just take a bit more time to set up the shot. This shot is about as little light as I'll generally shoot in and AF worked well here, if not all that quickly:
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A bit to my surprise, I actually find that at the same iso 3200 in the same lighting, I'm getting slightly faster shutter speeds with the GXR at f2.5 than I do with the X100 at f2.0, but I'm finding both very useable. The shot above came in at 1/50 and at closer to 1/30 on the X100. Of course, the X100 has a reasonably useable 6400, which the GXR doesn't, but I rarely go there, with 3200 covering about everything I'm going for. But I'd probably have trouble with snap focus at those speeds too, since I'm generally shooting with snap focus from the hip and more quickly. I'm sure I'm holding everything steadier held up closer to eye level and having to steady the whole operation to find AF. The PL25 f1.4 is an amazing low light lens, even on my epl3 which I never shoot above 1600. Part of it is the IBIS I guess, but I get great low light results with that. But its not a focal length I use out in the world much - most for family/friends types of shots in rooms that aren't that well lit. Same with the 45mm f1.8. When I'm out shooting, I'm just a wide angle junkie - its how I see stuff. As I've said, I've done OK with the 12mm f2.0 in reasonably well lit evening shooting, but not in the really dark stuff, although if the OMD will handle 3200, the combination of that and IBIS should make it a pretty decent low light camera with any of those f2.0 or faster lenses.
Here's a shot with the PL 25 wide open at f1.4 at 1600 on the EPL3 - it took the shot at 1/60, so you see there's not a whole lot more latitude there and this is the brightest of the m43 lenses (at least of the native AF lenses). And this scene wasn't quite AS dark as some of the others - you can see some blue sky beginning to show in the east...
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Finally, I haven't had much problem with flare/ghosting with the X100, but I'm probably just not that sensitive to it. Here are two shots in VERY low light with some direct light sources and I guess there's some ghosting, a fair amount in the B&W shot. They don't bother me, but they might bother others...
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-Ray