Just received my Canon L 50-300mm f/4.5 zoom and stepped outside my apartment to test it out on the moon. Here's the best shot. It is cropped from the original. Shot it at f/5.6 on the GH2 at the full 300mm zoom, the crop on the GH2 gave me a little extra zoom to an effective FOV of 600mm I believe.
Minor editing in photoshop, just some leveling to bring out some details in the bright side which were nearly washed out.
More tests to come!