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Usually the effect of a pinhole (or camera obscura) and the lens of our eyes are creating the world upside down on our retina.

Now imagine the lens and cornea would be flat is the pinhole effect still capable of creating a reversed image or would our vision be total blurred because (parts of) objects shining straight in the middle into our eye would not be reversed while parts above or beneath the middle would be reversed?

PS: This question is posted too at the biology.SE (not knowing where it fits best).

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  • $\begingroup$ Our eye's lens actually produces an upside image. Our brain turns it right side up when it processes the signals coming from the eye. $\endgroup$
    – NeutronStar
    Jun 6, 2017 at 18:02
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    $\begingroup$ There is no part of the image which is not reversed. You either have a pinhole small enough to give an image and this will be reversed. Or the pinhole is too large and the image is blurred. But still reversed, as much as you can see it. Neither the pinhole nor the lens produce a right image in this setup. $\endgroup$
    – nasu
    Jun 6, 2017 at 20:25
  • $\begingroup$ But what caused it to be blurred? Isn't that also because some light rays just traveled straight (so not reversed) and mixing up the image? $\endgroup$
    – Marijn
    Jun 6, 2017 at 20:28
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    $\begingroup$ Rays just traveling from the object do not produce an image. So without pinhole you have no image, just some light falling in the screen. This is the "blurr" if you wish. $\endgroup$
    – nasu
    Jun 6, 2017 at 21:52

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A pinhole camera, or a camera obscura, you can easily make yourself. It can actually be instructive to do this inside a darkened room, with a small hole to let in the light from the world outside. Yes, you get an upside-down image on the opposite wall.

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  • $\begingroup$ Would your answer be the same in case of the human eye? $\endgroup$
    – Marijn
    Jun 6, 2017 at 19:39
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    $\begingroup$ @Marijn If the lens and cornea were both flat, it would be a pinhole camera, even if it happened to sit in a human's head. $\endgroup$
    – rob ♦
    Jun 6, 2017 at 19:44
  • $\begingroup$ @Marijn I find your difficulty difficult to understand. A bit like the student who asked how a camera obscura "worked". So I demonstrated this in a darkened room - that gave him an aha-erlebnis. $\endgroup$
    – user137289
    Jun 6, 2017 at 20:14
  • $\begingroup$ I know that a pinhole works also reversed. I just made a small hole in a paper and put a flame behind it. But I just wondered what the maximum size of the pinhole could be to still show a reversed image. The hole I made was just about 1 or 2 mm wide. But I think that our eyes pupil is much wider......doesn't this eliminate the reversion for a great part? $\endgroup$
    – Marijn
    Jun 6, 2017 at 20:21
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    $\begingroup$ @Marijn Excellent that you did the experiment. A large hole will make the image blurry, maybe just a spot of light. But that spot of light will move down when you move the candle flame up. $\endgroup$
    – user137289
    Jun 6, 2017 at 21:07

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