Why is it that when a nearsighted blurry vision becomes clear when looking through a very small hole cutout?
In: Biology
If you imagine a piece of paper pointed at an outside scene, with nothing else in front of it. The paper will just be lit white, because it’s getting light from all over the scene in front of it.
The reason a hole does what it does is because it restricts the possible directions a particular point on the paper can be getting light from.
Now imagine the paper is stuck in the back of a box, that’s entirely enclosed except for a little hole in the front wall of the box. What I’m describing is pretty much a pinhole camera.
If you imagine the top left corner of the piece of paper. You imagine you’re looking from the point of view of that top corner of paper. You can see nothing, except what’s coming through that pinhole. But because it’s such a small hole, all you can see is what’s directly through the hole in the direction you’re looking, and that’s all. You can’t see what’s directly ahead of the box from there, all you can see is what’s directly in a line from that top corner of the paper, through the hole to outside.
If you imagine that’s the case for *any* point on the paper. If you’re in the middle of the piece of paper, you can see through the hole to whatever’s directly ahead of the hole outside. If you’re at the bottom right point on the paper, you can only see what’s out the top left of the hole, that kind of thing.
What that will actually do is be generating a fully focussed (but upside down and back to front) image on the paper of what’s in front of the box, just from the light coming through that pinhole.
That’s why looking through a small hole gives you a more focussed picture. Because it’s only letting a certain point on your retina see a certain point of the view in front, and nothing else. It’s doing just the same as what focussing with a lens would do.
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