The level of correction my eyes need seems to vary considerably depending on circustances; when I’m tired, late at night, etc. Since the focus of binoculars can be adjusted, has anyone ever made adjustable glasses?
Bi- or trifocals are probably about as good as you can get in any practical sense for the time being. Until someone invents a flexible lens whose curvature can be accurately altered in some way in the same manner as the lens inside the human eye, the only way to vary the focus is to have at least two lenses with the distance between them being variable. This would make for a rather bulky and uncomfortable pair of spectacles.
Well, those are less bulky than what I was envisioning, but still pretty ungainly. Any word on when they might actually become practical?
Nope. As far as I can tell, they’re still just lab curiosites.
I want a pair!
I remember seeing these a couple months ago. Not the coolest looking specs, but they can be made cheaply for third world countries. Certainly a clever idea, though.
There have been several different kinds of adjustable lenses over the years. Long before the adjustable bifocals given in the other thread, I knew a professor making switchable curvature lenses using electric fields. Before that there were several designs of adjustable lenses using liquids in mambranes adjusted by tension. And there have been lenses composed of pairs of fifth-order surfaces sliding across each other . And there have been glasses with flip-inlenses (like the ones the toy-fixer uses in Toy AStory 2.)
The thing is that most people don’t need adjustability over a range – they usually just need Near and Far. Couple that with the many parts used in these other contraptions, the potentially easily damaged parts, the many things that can get scratched or broken, and it’s easy to see why one-piece bifocals and Progressive lenses rule the ophthalmic world.