Panasonic GF1 has a Micro Four Thirds lens mount and currently there are 108 native lenses available for this mount.
Panasonic GF1 doesn't have a sensor based image stabilization system but 31 of these lenses already comes with optical image stabilization.
Since Panasonic GF1 has a Four Thirds sensor, it has a focal length multiplier of so you have to multiply lenses original focal length with this multiplier to find the Full Frame equivalent focal length of the lens when mounted on GF1.
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Panasonic GF1 Lenses with Image Stabilization
Panasonic GF1 Lenses with Weather Sealings