Heya. I've moved from a 550D to a GH4 and decided to keep the 50mm 1.8, so I got an EF- > m43 adapter. Out of curiosity, I tried to mount my 2 kit lenses on it, and it worked perfectly fine. The adapter didn't have the white dot on it so you had to place it slightly to the left of the red dot and try your chances. None of the adapters I've looked at specified that EF-S lenses would work; most said that they didn't. This then called me to question what I've heard about the metabones adapter and speedbooster being incompatible with EF-S lenses. As far as I'm aware, the lenses have a protruding mount ring that doesn't allow the lenses to be mounted on full frame canons, but seeing as it worked on this adapter, I wonder if it would've worked on the adapter with electronic integration, at least. My concerns are mostly about the speedbooster, and whether or not the protrusions would collide with the glass and pins. I do not have either of these adapters and, unfortunately, cannot test this myself. What I have been wondering aside to that is whether 3rd party lenses like Sigma and Tamron also have that same protrusion and whether they could be mounted. If not, then could the mount ring be replaced with the tradition ef ring on the lens and then mounted afterwards? The protrusion itself seems like a simple piece of plastic that protects nothing; an artifice to prevent any simple attempt at mounting EF-S lenses on full frame Canons. I'm wondering if anyone has tried to get around that in these ways. The biggest reason for my concerns is that getting a telephoto lens like the 16-300 would need the image stabilisation in the lens at long focal lengths; and at least the EF- > m43 adapter wouldn't have a glass element to collide with it,