[ame=https://www.youtube.com/watch?v=38Za5JD6vYE]4-12mm Tamron 1.2 on GH2 Lumix - YouTube[/ame]
Posted this video before but here's an alternative lens that WILL work on a GH2 - GF1 has no ETC mode, but you can always crop for photos.
CS mounts won't adapt to m43 cameras as the lens to sensor distance is too short (even without a mirror the flang distance is greater on m43).
1/2 rated C Mount lens or bigger is what you want. 1/2 inch will cover the frame using ETC mode for video. 1/3 is way too small and vignettes heavily for video and your pics would have to be cropped too much to even be worth it.
on a camera without ETC mode the bigger rating the sensor and longer the c mount lens, the less vignetting you get in general - ie a 35mm C Mount for a 2/3 inche or 1 inch camera would probably cover the GF1 for example, but a 35mm 1/3 inch would vignette. And to save you hours of googling info and wondering, the best you can get a 4-12mm range that is THAT fast is 1/2 inch, which will always vignette that wide.