Maybe biology, maybe physics. I’m not sure. Either way, I really can’t wrap my head around this
When I look in a mirror without my glasses on, everything in the ‘distance’ in the mirror is still blurry, but how can this be? All the light reaching my eye from that mirror is coming from the same place. The light can’t be out of focus before it reaches the mirror, so how come it can be when reflecting from the flat plane to my eye?
*Edit: I do understand how an image is produced in a mirror and how we perceive depth in a reflected image, but the fact is that the light is still reflecting off of a flat plane at a uniform distance – I can’t understand how that reflection can possibly have **actual** depth that can affect my shortsightedness*
In: Biology
You don’t actually see the world in three dimensions. You see it in two dimensions, because the light beams don’t communicate any information about the distance they travelled to reach your eye. Instead, we interpret depth, and kind of patch it back into the image the brain sees, based on things like like the angle of the incoming light – differences in the angle light must travel at to reach each of your eyes allows the brain to make a decent guess at how far away the object in question is. The more displaced an image is between the eyes, the closer it is. This is because when you look at a close object, light that bounces off it in a wide range of angles will all still reach your eye, whereas when you look at something further away, only a smaller range of angles of reflection can reach your eye.
Shortsightedness is basically an over-bending of light rays towards the center of the eye by the lens, which causes the focal point to occur a bit infront of your retina, instead of directly on it. This affects things travelling at quite straight angles towards you (ie, things in the distance), but doesn’t affect things where you can also see light that’s coming it at wider angles, because the wide angle light’s focal point is on the retina (it would normally be behind the retina).
Mirrors reflect light at the same angle as the incoming light, [but in the other direction](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fvoer.edu.vn%2Ffile%2F55384&f=1&nofb=1). This makes it appear as if the image has depth, because the angles of light that bounce off the mirror towards your eye are travelling at the same relative angle as the original light – only the more straight angles of an object far away will bounce off the mirror in the right way to reach your eyes, so it looks far away in the mirror too because it’s only the angle that the brain can use to determine distance.
That light is also travelling at the same angles that your eye bends to a focal point infront of the retina, so it creates an image in your eye in the same way light from an actual far away object does.
The image in a mirror appears a if it comes from a distance behind the mirror as the object is in front. Mirrors only reflect light beams, they don’t create an image, they are just a thin reflective layer, not a screen.
Because it is only reflecting the light, the mirrors “insides” are your room technically, with all the distances thatbare in there.
When we see something, it’s not as simple as the light flying from the thing to our eyes. Light shines from a source, like the sun or a lamp, scatters off the object in all directions, and then some of those rays hit our eyes.
But even if you’re looking at a single point, some of the rays will hit the top of your eye and some will hit the bottom. There will be some angle in between them. The lens in your eye bends these two rays (and all the ones in between) so they hit a single point on your retina. The closer the object is, the bigger the angle between the rays, and the more bending your eye has to do to focus them. The further away the object is, the more parallel those rays are, and the less the eye has to do.
Some people’s eyes are bad at bending a lot, so they can only focus on things far away – long-sighted. On the other hand, some people’s eyes are bad at bending a little, so they can only focus on things nearby – short-sighted.
When you look at something through a window, the rays that reach the top and the bottom of your eye don’t hit the same part of the glass. One hits slightly higher than the other. These rays stay separate the whole way from the object to your eye. The angle between them is based on the distance from the object to your eye, i.e. object to glass *plus* glass to eye.
The same is true for objects reflecting in a mirror. The ray that bounces off the mirror and reaches the top of your eye hits higher up the mirror than the one that reflects and hits the bottom of your eye. So, the angle between them is based on the whole path, i.e. object to mirror *plus* mirror to eye, *not* just the distance from mirror to eye. As far as your eyes are concerned, you’re looking through a window. The *image* you see on the mirror only exists in your eye – a *virtual* image.
This is different from watching a screen, where a point in the distance is still represented as a single point on the screen. The light hitting the top of your eye and hitting the bottom have come from the same pixel, so the angle between them is based on the distance to the screen. This is a *real* image on the screen.
I get exactly why you’re confused! Intuitively you’d assume that the light from the mirror is only travelling a fraction of the distance of the actual objects it’s reflecting so your short-sightedness shouldn’t be an issue if you’re close to the mirror.
Another comment put it quite nicely: our brains interpret depth by computing the angles that various light sources strike our retina. Objects far away will basically have a direct interaction with your retina with no effective angle of incidence and objects closer to you will strike your retina at varying angles. Short-sightedness impedes your brains ability to correctly interpret those direct light paths with no incidence angle (objects far away) due to physical malformations on the eyes surface. The malformations interrupt the lights direct path to your retina and your brain then struggles to interpret the information correctly. The result is the shifting of the eyes focal point, creating a blur/lack of focus.
With that understood, now consider how a mirror reflects the light. The reason a mirror appears to have depth despite being a flat surface is because the light striking it from the objects in the room are being reflected into your eye with the *same* angles of incidence that the objects themselves would, with the exception of the obvious lateral inversion a mirror causes. Your brain will interpret these various light sources striking your retina at different angles in the *same way* it would if you just turned around and looked at the objects directly *because the angles that the reflection and the true image strikes your eye are the same.* That’s the important part to understand.
The malformation in your eye that causes your short-sightedness (the shifting of your focal point) means that the objects that are far away, and the light they reflect from the mirror, strike your eye with little or no incidence angle and are therefore altered by the malformation, causing your brain to, still, misinterpret the information, causing the poor focus. The objects that are closer to the mirror will strike your eye at increasing incidence angles, avoiding the surface malformations and reaching the retina uninterrupted, allowing your brain to clearly interpret the image.
So, to satisfy the 5 year old criteria: brain can only use angles to work out depth. Mirror reflection shoots light into your eye at the same angles the real objects shoot light into your eye. The wonky eye messes with the light shooting from far away giving the brain the wrong angles. Far away objects get blurry.
The image in the mirror is not the distance from your eye to the mirror, it is the sum of the distance from your eye to the mirror and the mirror to the object you’re looking at.
Light is not like a laser, that flies straight into your eye. Normal materials scatter light that hits them, your eye does not catch on line of light, it catches a cone. This cone is then focussed onto your retina, like [here](https://www.iblindness.org/wp/wp-content/uploads/2014/06/pluslens.gif).
The further away something is, the less it needs to be focussed. Shortsighted people have either too long eyeballs or their eye focuses the light to early and it scatters again before hitting the retina again. Just like a magnifying glass, where you focus the sun on a spot and you have to hold it at the right distance of the spot.
Now a mirror does not send out a new cone, it does not scatter but reflect. It just bounces off a new cone that looks exactly the [same](https://qph.fs.quoracdn.net/main-qimg-3987582024b258e0c625e0352e9fcf9e). So you still need to focus it the same way as if the image were behind the mirror.
I can’t explain this to you, but I have the opposite experience. Things in mirrors are super clear no matter where they are as long as the mirror is close enough to me.
> *the fact is that the light is still reflecting off of a flat plane at a* ***uniform distance*** *-* *I can’t understand how that reflection can possibly have* ***actual*** *depth that can affect my shortsightedness*
* It’s not the distance that directly effects focus.
* It’s the relative *angle* of the light.
* The reason distance plays a part is because light spreads out over distance so the angle changes.
* Mirrors preserve the relative angle of reflected light, so the light keeps on spreading out the same exact way it would as if it was in front of you.
* You’re thinking about a mirror the way a display works.
* With a display, the light is emitted from the display and starts to spread out from there.
* With a mirror, the light starts spreading out when it leaves the object and *keeps spreading out at the same rate* when it hits the mirror.
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