If you have bad eyesight, how come looking into a mirror up close, doesn't help things that are far away?

Question

Ok, I have kind of bad eyesight...

The other day, I was looking in a mirror, and noticed that things that are far away are still blurry.

I turned around and looked at the objects directly, and noticed that when I look in the mirror, they are just as blurry as looking at them directly.

Why is this? It seems like since I am so close to the mirror, and am seeing it up close, that the objects wouldn't be blurry...

Thank you!

Thanks for the insults........ I have contacts... And I don't need to see a doctor, I was just asking a simple question... You'd think people in the Physics section would have a little more maturity...

Answer 1

It appears that you (like I) are nearsighted, and can't see distant objects. When you look into a mirror, your eyes must focus on the image, not the surface of the mirror. The image for an object 10 feet in front of a mirror is actually 10 feet BEHIND the mirror, not on the mirror's surface. So if the actual object looks blurry to you, so will the image; they're the same distance from your eye.

Answer 2

I've noticed this too. It all has to do with optical geometry.

In normal eyes (unlike the ones that you and I have), light is bent by the lens so that it focuses on the retina. The retina turns the incoming light into electrical impulses which are sent to the brain to be reconstructed into an impression of the world around us. When you're myopic, the eyeball is slightly misshapen so that light doesn't focus on the retina. The result is the same as if you adjust the lens of a movie projector so that the focal point isn't on the screen...you get a blurry image.

If you look at something far away, the rays of light from that object pass through your lenses at a certain angle to converge in your eyes (on your retina or not, depending on your vision). When you look at an object's reflection in a mirror, the angle of incidence upon your eyeball is essentially the same as it would be if you looked at it directly. That's because of a property of mirrors, they reflect light at the same angle that light strikes them.

So, looking at an object in a mirror is geometrically the same as looking at it directly. If anything, objects in a mirror should be slightly blurrier than they would be in real life since the light has to travel slightly further to reach your eyes (to the mirror first, then to your eyes).

I hope that helps!

Answer 3

Although the image is reflected in the mirror the light rays still have to travel a distance. You are near sighted. When you turn and look at the object, optically, it is closer to you that when you look in the mirror because you have added that extra distance.

Try to draw it out on paper. see what you come up with. Remember that the object is at the base of a cone and your eye is at the point. That holds true even when looking into the mirror.

Answer 4

Great question!

The answer is related to the angles at which the light beams travel.

Forget the mirror for a seconds, and say there's a tiny thing (say a small red LED light) that you're trying to focus on. It emits light beams at diverging angles; and in order to see the LED sharply, your eye needs to take those diverging light beams and converge them again (by bending them slightly), so that they all land on a single spot on your retina.

When something's far from your eye, its light beams make a very narrow angle (at the point where they enter your eye). When something's closer to your eye, its light beams make a wider angle. (At this point it may be useful to draw a diagram showing a near object, a far object, and your eye, and the light beams coming from the object. That will illustrate the "narrow angle / wide angle" thing, in case you're having trouble picturing it mentally.)

People with poor eyesight have trouble making the diverging light beams converge again. If you're nearsighted, your eye is good at converging the "wide-angle" beams, but not so good at the "narrow-angle" beams.

The point of all this is: what really determines blurryness/sharpness is the angle of divergence of the light beams coming from the object and hitting your eye.

Now, let's talk about the mirror. Say your face is against the mirror, and you're looking at the reflection of an LED that is 10 feet behind you. Because of the way light reflects off of a mirror, the beams from the LED that bounce off the mirror and hit your eye, will diverge at the SAME NARROW ANGLE as they would have if the LED were 10 feet in front of you. So if your eye is bad at converging narrrow-angle beams, the reflected LED will still look blurry.

On the other hand, if there's a little speck on the mirror, you'll see it clearly. That's because the light beams coming from the _speck_ will diverge at a wider angle at the point where they enter your eye.

Answer 5

That's because the light reaching the mirror is just as far as you would be seeing them without the mirror. The mirror is just a reflection of what you already see, although things may look smaller in the mirror.

Answer 6

Because the light from the object has to travel the same distance regardless of whether it is reflected in a mirror or you look at it directly.

Answer 7

well the mirror has a better but in the eyes directly at the object it is even more blurry give your eyes a rest or just get contacts

Answer 8

the objects are still far from the ,mirror. it is the mirror you are close to right? and the mirror just reflects, what is near looks near, what is far still looks far, and in your case blurry still.
hope i answered your question!

Answer 9

Yup you're dead right the punchline's much worse than the prawn cocktail thingy - it's so bad but ever so slightly funny that's all I'll give ya

Answer 10

You have "nearsightedness", you can see things close up just fine, but things further away are a blur...sucks getting old.

35 here and I have the same prob plus astigmatism. I want LASIK, but worry about risks.

Physics or Health question...Hmmm???