If it’s an emergency situation where you lost your glasses and you need to read something, all you need is a leaf and a tiny stick, or a piece of paper and a pin. Robert Krampf explains it at the Science Education Company.
I just tried his simple technique and it works impressively (though it’s not practical as a long-term solution).
Note to self: always carry around a leaf and a pin in case I lose my glasses.
That's totally cool, Erich. Thanks for posting the link.
This post deserves an encore. Here it is: How to polish your shoes with a banana. http://www.sonnyradio.com/bananapolish.htm
This same method works reasonably well without a pin: just squint your eyes. The resulting slit between your upper and lower eyelids will function the way a pinhole does to sharpen your vision.
BTW, a pinhole through cardboard, aluminum foil, tree bark, etc., will also make a handy pair of emergency sunglasses.