“How to See Without Glasses,”, the latest video by Minute Physics, offers a neat little trick for using your hands, should you lose your spectacles. Create a small hole with your fingers and hold them up to your eye to help bring things into focus. The method behind the trick is a quick insight into the physics of vision.
Unlike a lens, a pinhole or small opening can focus light from any distance. Because it’s such a small opening, it only allows light to come through in one place and thus in only one direction from any particular source so there’s no blur and everything is in focus.