Egami, the Japanese photography blog discovered a most interesting Canon patent that seems to enable a camera to use both the optical reflex and mirrorless systems in the same body. Interesting concept but I can't think of any practical use for it in the real world. Compromises will have to be made to both systems and the result may end up not doing the best job on either. A hybrid car is one thing. A hybrid camera?
Northlight Images provided the animation above and illustration below on how it might work.
"Short back focus lenses such as EF-M allow you to put the sensor much closer to the lens, reducing body depth. However, unless you choose an EVF, there is no way to get a good optical reflex viewfinder. The patent allows you to swap between a focus screen or sensor close up to the lens.
Perhaps a bit clearer to see in this animation of the short backfocus reflex viewfinder design.
The sensor is red and the focus screen green (other moving part is a mirror)
This allows a reflex optical viewfinder to be used with any short backfocus lens."