It's available on eBay with EF mount. It reduces aperture by 1 step and the reduction is 0.72x.
micro 4/3 focal reducer with EF mount
It reduces focal length of used lens to 72%, expands FOV (field of view) and makes the lens faster by +1 EV step.
EF bayonet is a great idea, because it gives you the opportunity to use many cheap EF adapters, like M42>EF, OM>EF, Exakta>EF, etc. So there's no need for buying various reducers. Frankly speaking, I haven't seen OM or Exakta version yet and I guess I'll never see it.
Always when it comes to any focal reducers the most interesting field of work are wide angles. On micro 4/3 cameras it's very easy to achieve any long focal length. Shorts or wides are the most problematic one.
Luckily Tokina manufactured a very interesting lens for Canon (and other systems): 11-16/2.8.
It's a very wide angle lens designed for APS sensor cameras in various mounts. Since we have access to Canon EF mount FR (focal reducer) lets stick to it.
I encourage you to take a look at very nice test of Tokina AT-X 116 PRO DX II AF 11-16 mm f/2.8 on www.optyczne.pl
As my friend recently wanted to buy the lens, I've read a lot about it.
It has EF mount (not EF-S!) and according to the test above it has flat bayonet part at 11 mm. At 16 mm rear lens unit goes inside about 1 cm. It means there won't be any problem with FR lens.
Luckily, tests were also taken on FF (full frame) DSLR, which provided us perfect vignetting sample chart.
After taking some measurements and making drawings of sensor sizes it turned out that at 11 mm, Tokina would slightly vignette on the corners, but would have a focal length ca. 8 mm and aperture of 2.0.
It's an equivalent of 16/2.0 for 135 (FF) format.
That makes Tokina with RJ's Focal Reducer one of cheapest wide angle lenses for Micro Four Thirds cameras.
Unfortunately there still would be an issue of no aperture control, but hey - Rome wasn't build in a day!
vignetting samples from:
Tokina AT-X 116 PRO DX II AF 11-16 mm f/2.8 on www.optyczne.pl - vignetting