Not strictly photography related, but I figured I'd get

>>3001636
Your premise sounds like it could be the case but I don't know enough to say for certain whether or not you're correct. It is an interesting question.

I can shed some light on your bonus question though. Camera lenses can indeed be made of plastic! Good ones even! Although most high-end lens makers only use "optical resin" for smaller elements inside telephoto lenses to correct for chromatic aberrations. They can actually be really expensive, more so than the glass elements in some cases. Plastic doesn't make a good front element though because it can be scratched and pitted easily. I could be wrong but I also think glass is easier and cheaper to get "optically perfect" for use in a camera lens. Your glasses lenses are just one lens and pretty specific to you, not a mass manufactured lens for a popular camera system.

>>3001657
Thanks

File: myopia-hyperopia-illustration-condition-eyes-their-correction-40924891.jpg (39KB, 400x384px) Image search: [Google]

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If you have good vision and you put a lens in front of your eye then it would impair your vision in the opposite direction. So wearing a negative power lens made for correcting nearsightedness would effectively make you farsighted.

>>3001694
This
It's just moving your focus range
In photographic terms, it's like putting a lens on an extension tube or on another mount with shorter flange to focal plan length.

>>3001719
It's not really like an extension tube, it's a diopter like when you put one of those close-up macro filters on your lens to get it to focus closer but then the lens can't focus to infinity with the filter attached.