When Canon announced the Canon EOS M Mirrorless camera, it also announced the Canon Mount Adapter EF-EOS M. This small and lightweight adapter allows Canon EOS-M camera owners to mount their EF and EF-S lenses. As for the time of writing this post, Canon introduced only two EF-M mount lenses, the Canon EF-M 22mm f/2 STM and the Canon EF-M 18-55mm f/3.5-5.6 STM IS.
Canon EF-M lenses will be relatively smaller then current EF and EF-S lenses, and that due to the fact that the camera doesn’t include a reflex mirror, like in DSLR cameras. I guess that there are many people who already considering buying into Canon Mirrorless system, some of them might already have some Canon lenses. Others might have someone in their family that have a Canon camera and own a few EF or EF-S lenses. So by purchasing the EF-EOS M adapter, they have the option to mount the lenses and use it with the EOS-M camera.
The thing is that right now Canon only announced two lenses, so if you buy the EOS-M, maybe you should keep some of your lenses and use them. Of course it’s not the ideal solution. I can’t see many people mounting a 70-300mm lens on the EOS-M, it’s just to big and heavy, and it loses the whole idea of having a Compact System Camera in the first place. I believe that Canon have a lot of new products to announce, including more lenses for the EF-M mount.
If you buy the ED-EOS M adapter, you can mount many type of lenses, including wide-angle, fish eye and macro lenses. Those lenses will probably be available for the EF-M mount, but it will take some time. I’m sure that many of you already consider using the EF 50mm f/1.8 on the EOS-M. The Canon mounter adapter and the EOS-M can even serve professional photographer as a backup camera.
The adapter also includes a removable tripod mount, which support heavy lenses when you mount the EOS-M on a tripod. Also note that you can attach the Canon EF 1.4x III and EF 2x III extenders to the adapter.
I think that Canon has made a smart move announcing the adapter at the same time it announced the EOS-M camera.
For those who are interested to see how some EF mount lenses look on the Canon EOS M, take a look at this camera + lens comparison on camera size website. You can see the following lenses: Canon 17-55mm, Canon 24mm, Sigma 150mm f/2.8 Macro DG HSM, Canon 50mm f/1.4 and the Canon 85mm f/1.2 lenses. You can see what it’s not an ideal to use EF / EF-S lenses with the EOS M.