When you go to the optometrist they test your reading by flicking you through many different lenses. Of course there are a finite number of lenses in their possession, so they can only correct your vision to some precision. if one could in principle make custom lenses precisely for a person’s eye, could one theoretically have perfect vision
? and how far would you be able to resolve images on a clear day?
In: 3
So light is a wave, right? And waves aren’t really *at* a single point: they’re kind of spread out. So it turns out that even with *perfect* lenses (or mirrors, but we don’t have those in our eyes usually) we can’t focus light emitted from a single point back into a single, perfect point. There will always be a fundamental blurriness due to the wave nature of light.
This limit is called the “diffraction limit” and it gets smaller (i.e., our vision would get sharper if everything in our eyes was perfect) if the wavelength of light is shorter (meaning bluer) and the aperture — how big the opening that lets light into our eye, with the lens width as an upper limit — is.
Surprisingly, our eyes can get pretty close to the theoretical maximum diffraction limit. Exceptional 20/10 vision corresponds to an angular resolution (how small an angle two points can be separated by and still be seen as two distinct points) of about 30 arcseconds. The diffraction limit for the human eye is no less than about 20 arcseconds (and some sources report it to be even worse), so 20/10 vision is pretty close to the theoretical limit for perfect optics!
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