Canon recently introduced the Canon EOS M, mirrorless interchangeable lens camera. It uses a new EF-M mount and is available as a kit with an EF-M lens in some regions. I have existing EF and EF-S lenses from my Canon 40D, will these work fully on the EF-M mount camera?
Canon also announced the Canon Mount Adapter EF-EOS M when they announced the EOS M camera. The adapter is said to be available in October 2012 for $199 USD. It is compatible with the full range of EF and EF-S lenses that are currently available. This also includes the full range of third-party lenses that currently work with the available EOS bodies.
The adapter specifically extends the EF-M flange distance(bayonet to the sensor) from 18mm to 44mm that the other Canon DSLRs have.
One nice feature of the adapter is that it has a built in tripod mount. This can come in handy when mounting a larger lens to the smaller EOS M body. One example of a very large full size lens being used with the adapter can be found here, where they test it with an EF 800mm prime lens.
So any lens that you have that works with the Canon 40D should have no problem with the EF-M mount EOS M camera body, using the adapter of course. This means full functionality such as autofocus and lens information. I have yet to test out the implementation to see how autofocus actually performs with this setup, but early reports seem to be positive from what I have found.
Canon says yes. Some big lenses are going to look really silly on that tiny body.
The M has a different type of auto-focus, more like video cameras and less like other DSLRs. Many pocket cameras have really slow auto-focus.
I'd wait until some reviewers have had a chance to actually test the production models and see if the AF performance is good enough.