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In optics it is widely mentioned real images are projectable onto screens whereas virtual ones can only be seen by a person. Isn't that contradictory? I mean in order to see the virtual image it has to be projected onto the retina (ultimately acting as a screen).

So, why can you see virtual images in the first place?

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up vote 20 down vote accepted

Your eye is a second optical system.

It re-focuses the diverging rays to produce a real image on the retina.

This process is exactly the same thing it does when looking at a nearby (i.e. not at effective infinity) object.

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Thanks. There are some people telling it's due to the brain performing [magical] operations upon the visual data. –  artistoex Mar 7 '11 at 17:31
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Dear Aristoex, there's a lot of operations being applied on the image on the retina, but it's still true that there is a real image on the retina. It's upside down. So of course the neurons etc. are connected in such a way that the brain realizes that if there's something at the top of the retina, there is something at the bottom of the reality, and vice versa. This up-down flip is trivial but some people love to present it as magical. However, the optical information on the retina is purely geometric and doesn't need any complicated transformations to look real. –  Luboš Motl Mar 8 '11 at 9:25

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