I am nearsighted. I noticed when I was a kid that if I looked through a small hole ( about the diameter of a pencil lead) without my glasses I could see clearly. What is the mechanism behind that. would glasses made with a pinhole on each lens work? granted the field of view would be less, but if you are like the guy in the twilight zone maybe this could hold you off til you find a decent pair among the wreckage of civilization.
Because you are forming a pinhole camera and using only a very small area of your eye lens so that its imperfections are insignificant.
I think it’s for the same reason that decreasing the aperature on a camera lens gives you greater depth of field. Here’s one way to think about it. If something is in focus, a point on that thing will correspond to a point on your retina (or a camera’s film or CCD). If it’s out of focus, a point on the thing will give a spot on your retina. The size of this spot will depend not only on how out of focus it is, but also on the relevant aperature (normally your pupil, but smaller if you look through a pinhole).
I used that effect last night to watch TV. I had just taken out my contacts, and because I broke my last pair of backup glasses I viewed through a comb. Works like the pinhole.
A pinhole requires no lens at all to create a perfect image, but of course the hole has to be perfectly small. The narrower the hole, the smaller the points of light that hit the retina, and the better the image.
What tricks you about it is that with so little light getting through you can’t understand how you can see at all. But the part that adjusts contrast to fit available light is in the brain, not the eye.
A solar eclipse provides a really nice demonstration of pinhole optics. If you look at the spots of sunlight shining through leaves during an eclipse, you’ll see that they take the shape of small images of the crescent sun.
Some animals (octopus?) actually have an eye focus system that works like that.
I also found this out when I was a kid. I was also nearsighted, but no one knew it and at five years old I didn’t know enough to tell anyone. Someone told me I could look at the sun through a pinhole in a piece of paper without damaging my eyes. So I did. That was the first time I realized that the sun is round. Then I started looking at other things through the pinhole, and discovered that everything looked a lot clearer. So I told my mom about it, and she took me to the eye doctor, and that’s how I got my first pair of glasses!