All I know is that some lense moves somehow, but why does that make certain parts in your field of vision go blurry, while one is clear?
In: Physics
Defocus is one of the simplest optical abberations, it’s caused by the lens being too close or away from the focal plane, the ratio to what’s in focus and out of focus is called depth of field and it changes depending on how big the aperture is.
Focusing is just moving a lens back and forward until the image is clear on the focal plane, you can try this yourself, use any lens and attempt to focus a bright scene onto some paper, at a distance it will be a circle of light but at a certain distance it will be the image, upside down of course, that’s how camera lenses focus, a lot of cheap cameras have no focus but a small aperture and lots of depth of field to make up for that.
Your eyes work a little different, the lens isn’t glass, it’s crystaline and it’s maintained by your body, this is why it loses power as you get older, your eyes lens actually changes shape to focus, but it’s still not easy to get an out of focus background, your eyes aperture is still very small giving a decent depth of field, unlike a professional camera lens that can give a really blurred out background, your eyes still have a minimum focal distance (at some point or another it will be really hard to focus on an object close to the eye) but they can of course focus to infinity, failure of your eyes to focus to infinity is short sightedness, unusually far minimum focal distance is caused by long sightedness, both of these can be corrected with a lens that either has a + dioptre or – dioptre depending on the error, negative lenses diverge light, they can be combined with a normal converging lens to project a really wide ‘fisheye’ image
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