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.
Huh, that definitely explains it. I wonder how many people know that. In that case it's particularly unfortunate to downvote the OP simply for filling a field in the submission form! Sigh… I guess it's another case of LLMs having made the world a little worse for everybody.
But the articles are well-researched, very high quality (the illustrations in particular are incredible), and in every way prime HN material, and there's no money involved as far as I can see. I definitely don't have any qualms about self-promotion of this sort of stuff.
Personally, I’ve only ever provided a summary if I felt the headline wasn’t clear enough.