Originally Posted by Manofmayo
The Canon EOS RT and EOS 1N RS are two such cameras. They used pellicle mirrors as someone mentioned earlier in the thread.
Originally Posted by wickerprints
You bring up a good point. Another potential downside is that certain microlens designs cause sensors to have a low angle of response, so that non-telecentric designs reduce the amount of light gathered. This was one of the claims that Four Thirds marketed about their telecentric designs (though I'm not sure it was ever real since they've silently abandoned it and they're dramatically reversing their lens designs). I've read that modern microlenses are much better now (more so than than bare silicon and better than film too).
Personally, I think I'd much prefer the non-retro-focal (rangefinder) designs, because I can live with the dramatically increased vignetting in order to get better distortion, flare, C.A., and contrast. But I don't think Canon will come out with such designs for a very long time, because they could only market the lenses to owners of the new cameras (if and when they come out).