Okay, so let me see if I get this right... if I want to shoot video with the GH1 and am using some Nikon, Canon, Tokina, Voightlander, or other similar lenses then it's approximately a 2x crop factor? So a 20mm becomes approximately a 40mm FOV? Is there anything out there (similar to a focal reducer) that will squeeze the image circle by about .5 or .6 to better fit the sensor? Could be a great accessory for 4/3 and micro 4/3 cameras.
Right. If you're looking for Full Frame FOV comparisons think old school movies that were shot Vistavision.
So a 20mm does become a 40mm.
If you're trying to figure out what it looks like on a 35mm Film Camera or RED @ 4K, it's more like a 28 or so.
Focal reducers I'm not sure about. It's funny though, soon none of the light gathering stuff will matter because sensor technology will improve and a 2.8 will be the new 1.2.