This article presents the inventive solutions Canon has found to shoot beams of light into the camera's viewfinder in order to light up individual autofocus points. Six different approaches are shown using six Canon DSLR models between 1994 and 2009.

It's absolutely wild to me that this function would be so important as to justify all the time and effort to create not just two, but six entirely different ways of solving it.

The first one seemed perfectly adequate to me. But I guess that's why I'm not a Canon engineer.