Crop factor applies to ALL lenses for a given format and it is the same for native lenses and non-native lenses. The crop factor for all lenses used on a micro four thirds body is 2.
Focal length doesn't change, regardless of format. For instance, if you get a legacy 24mm wide-angle lens from a film system and mount it on a Micro Four Thirds body with an adapter, it will give an almost identical field of view to the native Panasonic 25mm.
This image explains it quite clearly: ie: the image (what the lens produces) in itself doesn't change, just the area that the sensor in question is capable of capturing. (Field of View) Depth of Field, and all other optic aspects of the image stay the same regardless of crop factor (sensor size). EDIT: You can take a picture with similar Field of View as a 35mm (full-frame) sensor camera with a 100mm lens with a micro four thirds camera with a 50mm lens BUT! DoF and all other optical properties WILL change also. EDIT2: Even more info: {} And link: http://en.wikipedia.org/wiki/Crop_factor
