I've had the Leica DG Summilux 25mm f/1.4 in for review for a while and I thought I would post my initial impressions. In terms of size it looks quite large on any of the tiny Olympus PENs though it doesn't feel cumbersome in any way. Why would you want to match this to a PEN? Well to benefit from the excellent built-in image stabilization for one and also to see the results of Olympus' excellent Jpeg engine. Panasonic supplied the GH2 with the 25mm Lux and it handles and balances well.
In terms of image quality, it has outstanding color rendition and terrific micro contrast at maximum aperture but the latter improves across the frame two stops down from the maximum. There's some axial (longitudinal) chromatic aberration visible but it's common on wide-aperture lenses. I like the 50mm (equivalent) field of view for environmental portraiture, and focusing is blisteringly fast on the GH2, though it's FoV won't be for everybody. However, this is a lens with exceptional imaging quality and to my mind an important addition to M3/4 system.
I've also had in the Olympus 45mm (90mm-equivalent) f/1.8, and that is much smaller, almost too small on the GH2 though it handles superbly well on my PEN E-PL2. I hope to post some early sample shots with that too.
The Panasonic made Leica DG Summilux 25mm f/1.4 on the tiny E-PL2 is a brute but handling and imaging is superb. Taken with a Panasonic GH2 with Olympus 45mm (90mm-equivalent) f/1.8 at f/5.6, ISO1600 (below).
For those wondering what the outstanding 45mm f/1.8 looks like on the GH2, here's a picture taken with the Olympus E-PL2 and Leica 25mm f/1.4.
Excellent color and micro-contrast (this looks washed out in some browsers, try a color aware browser such as Safari). Panasonic GH-2, Leica DG Summilux 25mm at f/1.4, ISO160.
Autofocus is surprisingly fast on the GH2, fast enough to focus on the seagulls in the foreground. Panasonic GH-2, Leica DG Summilux 25mm at f/1.4, ISO160.
1:1 crop at f/2.5 from an out-of-camera Jpeg, shows superb micro-contrast. Panasonic GH-2, Leica DG Summilux 25mm f/1.4 at f/2.5, ISO160.