Good illustration. Here are some thoughts that occurred to me when studying it:
  1. How does this schematic change when the reflex mirror is changed to a fixed pellicle mirror as found in the earlier EOS-1N RS? We know it is possible, but I am not sure how the AF system was redesigned to account for a fixed mirror. My understanding was that this camera contained 5 AF points arranged in a horizontal linear configuration across the middle of the frame. (We have come a long, long way since then, haven't we!)
  2. Given the geometry in the diagram, there does not seem to be any reason why the AF mirror and sensor assembly cannot be made wider--that is to say, it could conceivably be made to stretch lengthwise across the frame. This would not be reflected in the cross-sectional diagram. There must be other considerations as to why this is not done.
  3. I can see that one theoretical modification to this geometry which would enable greater vertical coverage would be to use multiple AF mirrors, the height of which would form a geometric progression. That is to say, the bottommost mirror would cover the bottom half of the frame, a second mirror would cover the quarter extending from the horizontal mid-line upward, and so forth. Of course, this is not practical, but in theory, multiple AF mirrors would enable greater coverage. The problem of course is that this drastically increases the complexity of the mirror assembly, and would create horizontal gaps where the mirror attaches to the main reflex mirror, where no AF points could be placed.



I agree that an electronic viewfinder would be the future, given that contrast-detect AF is not yet fast enough to yield satisfactory performance. However, this raises questions about how to deal with the behavior of the shutter, presuming that the main imaging sensor is used as the VF.