Tom
You are feeding my GAS!
Andrew
--
Infinite are the arguments of mages. Truth is a jewel with many facets. Ursula K LeGuin
I would not rush out and actually buy a Canon EF lens specifically because of these adapters. But I agree with Neil that the 40/2.8 STM Canon lens does work very well adapted to M4/3 body.
The Kipon adapter seems to be getting more capable by the fimware upgrade and is cheaper but my opinion is that Metabones have "cracked it" with the v1.8 firmware release and it is now fully capable on the Olympus bodies as well as the Panasonic ones - and Metabones has three adapter versions to choose from.
However anyone with a closet full of nice Canon EF lenses can now put hem to very good use on M4/3 bodies as small as the GM1. For a laugh only I fitted a GM1 body on the huge 400/2.8 IS lens and it made perfect quick auto focus! I suppose that as this lens is only useful on a tripod anyway the actual size of the camera body is therefore a moot question if it works. But the PDAF E-M1 and battery pack is going to turn this lens into a big reach all day monster in other ways as well - either a FF eq 800/2.8 or with an Ultra speedbooster it make it a 280/2.0 in M4/3 or 560/2.0 in FF eq terms. But you need the entry fee and it is a very big lens.
On the other hand those who need and can justify such a lens now do have a means of attaching one to a M4/3 body with good AF-S at least. How long before Olympus (or Panasonic) provides something similar in native mount? This is a very specialist field of use with high entry fees and low sales numbers.
My present favourite is the still very expensive, hand held capable, but borderline carry about 200/2.0 IS (at about 1.9Kg for the lens alone). This is working, in my experience, just as well on a M4/3 body as it ever did on a dslr body. But contrary to my past practice I have actually now used it on an E-M1 whilst being carried about to the wry amusement of some pop-eyed passer's by. But I admit to have also used it on a NEX6 indoors quite successfully as well. I had to tell them "it's only "a 200", and many kit lenses have greater reach" to disabuse them that I was using it to peep through lighthouse windows. Such big object lenses give some the impression that you are checking out landers on Mars.
In indoor light on a focal reducer f1.4 on a 200mm prime reduces the dof to perhaps 1 metre maximum. Must be magic for indoor sports though.