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Autorefractors are being used by eye opticians for eye diagnosis. I searched internet for articles and wiki page as well but I wasn't satisfied. I am interested to know how do they actually work. How the machine is able to focus sharp on retina automatically. How do they figure out spherical/cylindrical aberration for human eye. I even asked optician as well but he tricked out of this position saying it does all happen automatically. LOL!

A detailed answer would be much appreciated. Please don't hesitate to write any technical details or mathematical derivations. I would love to know how these machines actually work.

Thanks in advance!

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    $\begingroup$ The autofocus article suggests that it has something to do with phase detection $\endgroup$
    – Loourr
    Commented Jul 13, 2013 at 17:57
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    $\begingroup$ The following file(pdf) explains the subject: $\endgroup$
    – user31399
    Commented Oct 20, 2013 at 11:37

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the autorefractor projects an image into the eye. the light rays pass through the lens and strike the retina. a small amount of the light bounces off the retina, passes through the lens a second time and exits the eye. Imperfections in the shape of the eye's lens distort and defocus the "return" image. the autorefractor senses the distortions and misfocus and tweaks the projected image with lenses of its own until the "return" image is in focus and distortion-free. the software in the autorefractor then deconvolves the tweaks and back-calculates the corrective lens prescription that the lens in the eye needs to properly focus the image.

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