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The images we perceive through our eyes are formed by focusing the incoming light with the eye's cornea and lens. The information is "captured" by the retina and then transmitted to our brains through the optical nerve.

Cameras emulate our eyes, but instead of cornea and lens, cameras have different types of lenses and instead of retina they have a sensor.

In both cases, the image being "captured" is a focused (and also flipped upside down) version of the combined light that is hitting the lenses.

So it seems like, to make sense of the light we perceive, we (need to) focus it in a certain way to generate the images we see.

What does the world "look like" without focusing it through our lenses? Would we be able to see anything at all?

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    $\begingroup$ Loosely stated, lenses are used to focus light beams. I think that you'd see everything extremely blurred as without a lens you can't focus any light. Maybe you could pick a relatively cheap ccd camera and take out the lenses and take a picture and see what happens. I also found this so that seems to be a thing people are investigating for various purposes. ncbi.nlm.nih.gov/pmc/articles/PMC3477589 $\endgroup$ – Bonsay Aug 16 '19 at 7:43
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    $\begingroup$ Lensless imaging is a thing - i.e. there are other ways to do imaging that don't require lenses. Is that what you're asking? Or are you asking what happens if you remove the lenses and do nothing else? $\endgroup$ – Emilio Pisanty Aug 16 '19 at 12:35
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    $\begingroup$ If it's the lens of your eye that's missing you would then have the condition known as Aphakia en.m.wikipedia.org/wiki/Aphakia, and reportedly along with it a very limited ability to see some UV light as one role of the lens is to block UV light. $\endgroup$ – Triatticus Aug 16 '19 at 17:45
  • $\begingroup$ @Triatticus that is super interesting, thank you for the info and the link! :) $\endgroup$ – Nico Brenner Aug 16 '19 at 18:02
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    $\begingroup$ First of all, you have to realize that without an observer to 'look', the world doesn't 'really look like' anything :) But to be more indulging to your question: 1. without a lens, we would just see all objective blurred together, but of course the world isn't a blur. 2. The best objective representation of the world would be an image from a telecentric lens (without perspective errors), and a hyperspectral camera (which is not limited only to visible light). $\endgroup$ – Yuval Weissler Aug 19 '19 at 4:59
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The purpose of lensing is to present us with information about light reaching us from specific directions. Light from one angle is sent to one part of the retina, and light from another angle is sent to a different part. So fundamentally that is what we are thinking about when we try to ask "what is the lens doing?"

There are other ways to achieve this directionality. One approach is that of a pinhole camera. If the light has to go through a small aperture , the effect of doing so will also separate out the light rays by the direction they come from. If you put a really tiny hole in front of your eye, it would focus the light without requiring a lens. This does indeed happen in the eye. We can focus better in bright light, when the pupil is constricted, making it more like a pinhole camera.

Of course, we can also relax the requirement of trying to get directional information. There are blue-light sensors based on cryptochrome inside our skull. They mediate neuron activity. There's still ongoing research into why our bodies do this, and how much of an impact they have, but it points to what you would get if you had no focusing mechanisms available. You would merely be able to say whether you are in a bright area, or a dim area.

Indeed this is along the lines we believe the eyeball evolved. Sensing changes from bright to dark are an excellent way to detect a large predator nearby.

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