Ask anyone about Canon’s mirrorless cameras, and one of the first complaints will likely be about the AF in general, but even more so when paired with EF or EF- S lenses via the Canon EF to EF-M adapter.


A new patent discovered by Egami shows that Canon could be developing another version of the adapter which would, among other things, offer an improved AF performance by EF and EF-S lenses on an EOS M body.


Patent Details

Patent Publication No. 2015-34903

  • Published 2015.2.19
  • Filing date 2013.8.9

Master lens

  • Zoom ratio 2.69
  • Focal length 72.13 135.02 193.99mm
  • Fno. 2.90
  • Half angle ω = 10.72 5.78 4.03 °
  • Image height Y = 13.66mm
  • Overall length of the lens 237.36mm
  • BF 54.00mm

Adapter installed

  • Zoom ratio 2.69
  • The focal length f = 72.12 135.00 193.96mm
  • Fno. 2.90
  • Half angle ω = 10.72 5.78 4.03 °
  • Image height Y = 13.66mm
  • Overall length of the lens 239.70mm
  • BF 16.77mm

Canon patent

  • Fast AF adapter
  • Wobbling corresponding
  • 3-group configuration of positive and negative positive
  • 2 group also serves as a focus group and the anti-vibration group
  • And realize high-speed AF focus group was lighter

Personally, I feel like this sort of a futile effort given the current crop of EOS M cameras. They are all way too small to make using full sized EF lenses practical. If Canon has any larger, more SLR styled mirrorless cameras (a la Fuji X-T1), then I feel that an adapter like this would make much more sense.

That said, the AF with the current adapter is pretty poor. Users can autofocus fairly well on Sony cameras with the EOS adapters they have, so you would think – if for a matter of pride alone – that Canon could produce an adapter that gave good AF performance on their own mirrorless cameras.

Anyway, it will be interesting to see what comes of this.