Micro four thirds - does the crop factor apply to MFT lenses as well?

A lens has a particular focal length and aperture determined by the lens construction. The lens is the same lens whatever camera you put it on. The "crop factor" is a result of using a sensor of a different size to that of the 135 standard (a.k.a "full frame 35mm SLR") and not the result of using a lens dsigned for a particular system.. The combination of a lens (of a particluar focal length) and the crop factor (of the camera sensosr) gives rise to an "effective focal length" of the lens in question. This is only an "effective" change since the lens does not actually change its focal length. The crop factor for 4/3 sensor based cameras (i.e. Four Thirds SLRs and Micro Four Thirds MILCs) is 2, for APS sensors it is 1.6 (depends on exact sensor size), for compact cameras it is typically around 5.2 or 5.6. For medium or large format cameras it will be a number between 0 and 1, i.e the reults of the "crop" is larger rather than smaller.

Now lenses designed specifically for MFT only have to create an image circle that covers the small 4/3rd sensor so they can be designed smaller and lighter than lenses of identical focal length that have to create a bigger image circle to cover a 35mm sized sensor. A MFT lens used on a 35mm camera (ignoring the physical constraints imposed by lens mount that make this impossible in practice) would results in severe vignetting as the image would not cover the corners of the sensor. The same situation applies to the 2 lenses designer for the EOS-M format.

So, the crop factor does not apply to MFT lenses per se, but since you can only use them on MFT cameras (or cameras with a smaller sensor) you will always need to apply the crop factor for that sensor to get the effective focal length of the MFT lens.