I've seen a questions in the speedbooster topic and saw a similar question in a DPreview thread.

"Has anyone heard if there will be a Speed Booster for m43 LENSES on m43 bodies"

people say it can't be done because the m43 lens is built to cover a m43 sensor and this does seem logical. However (and i'm probably thinking way off here) the m43 has a cropfactor. FF does not. I always thought the FF lenses were so expensive because the entire lens has to be perfect as the entire image falls on the sensor. Where a lens designed for a cropfactor camera needs to be sharp mostly in center and not on the outside as that will not hit the sensor anyway.

So my thought was, if a GH3 has a cropfactor of about 2X, doesn't that mean that part of the total image is cropped? If so then i don't think that question for a m43-m43 speedbooster is such a strange question. As only part of the image actually hits the sensor.

So a speedbooster (i know, probably impossible) would then widen the FOV and increase DOF on m43 lenses and decrease the F-stop.

Off course there will be a lot of vignetting but still when i buy a 50mm lens for m43 that 50mm is what it would be on a full frame camera, we get a cropped version on the m43 camera but the full 50mm image has to be there for us to crop our image from.

In this video they do it the other way around: cropsensor-lens on FF camera

Could someone please explain where i'm wrong in my thinking?