So I finally got my GH2 and had some time to compare the GH2/100-300mm to my Canon 1DsII with 100-400mm L. The results were very surprising to me. The Panasonic GH2/100-300mm combo was stunningly good, and absolutely held its own to the Canon Combo.
Test conditions:
Everything on a tripod (Gitzo 3 series) using remote release, Image stabilization off, and mirror lockup for the 1DsII. Auto focus was used for both, but the focus point was set for the same flower (the one shown in the images below). Images shot indoors with natural light at about a distance of 15-20 feet. Images captured in Raw formats, opened with Lightroom 3 with no sharpening or noise reduction applied. They both sharpen up a lot with some small local contrast addition using Dfine, but that is subjective so I left that out. Here are some crops from shots taken at about 200mm on the Panasonic and 400mm on the Canon. I took shots at f/5.6, but the canon images were ever so slightly blurred. I am guessing I was too fast with the shutter release after mirror lockup, so I do not think that shot was indicative of the lens/camera combo. So I used the f8.0 shots taken below. My first reaction was wow, the Panasonic really had equal or even slightly better detail. The panasonic enjoys a slightly greater depth of field which we would expect. The color renderings were really different and surprised me with both cameras being on auto and the lighting did not change in the few minutes between shooting with each setup. The canon is much warmer. The one area which will be hard to see in these is the shadows. The Canon has some banding, while the Panasonic is, to my eye, cleaner. I will have to see if I can show that later. Overall, I am very impressed with the GH2 and the 100-300mm.
Full image from GH2/100-300mm:
Crop from GH2/100-300mm at 200mm f/8.0
Crop from 1DsII/100-400mm at 400mm f/8.0