[colonel_panic]

More importantly, it explains why both the world and the overlays appear in focus. I have yet to see an explanation for how Project Glass does the same. Apparently it's based on the same technology that went into Babak Parviz's contact lenses, which use Fresnel lenses to make the overlay appear in focus when your eye focuses on real-world objects several feet in front of you. Fresnel lenses also impair image quality. And you'd need another lens on the opposite side to undo the projection on light coming in from the world around you.

I'm wondering whether the reason that Google's glasses only use a small display in the corner of one eye is that the see-through image quality is simply not good enough to justify covering the wearer's entire field of view. If you look at the photos of Sergey Brin wearing them, they are not very transparent, at least from the angle the photos were taken: http://www.theverge.com/2012/4/6/2929927/google-project-glas...