this post was submitted on 05 Jun 2025
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When your eyes are open and unobscured, light is coming in from every direction. The lens is shaped in such a way that light rays parallel to the eye's axis are focused on the macula, the center of your sharp vision. A near-sighted (myopic) eye focuses those parallel rays in front of the retina, and a far-sighted (hypermetropic) eye focuses them behind. The farther away the ray is from the eye's axis, the more it is refracted by the lens, and the more obvious its out-of-focus-ness becomes if the lens has an incorrect shape.
Corrective eyewear works by refracting the light before it enters the eye and essentially cancelling out the lens' imperfections.
A pinhole works by obscuring light rays that are farther from the axis and contribute to the blurry image, only letting through light rays that are near the axis, already aligned more or less with the macula, don't have to be refracted as sharply, and don't contribute as much to the blurry image. This is why the camera obscura works, and why apertures in modern photography are used to control both the image's exposure and the strength of the depth of field.