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
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.
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