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
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.
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