I'm nearsighted - so why are things in MIRRORS blurry?

This question has been bothering me for a while, and the response about the remote control and the mirror seemed to jar it loose so here goes, and pardon me if I’m redundant, but here goes:

My eyeballs cannot see far distances yet reflections in mirrors also display things at a distance as fuzzy. I mean - I’m not really looking at the Van Halen poster 10’ behind me - I’m looking at a flat surface 6" from my eyes that reflects light, right? What gives? Thanks for any and all responses!

But your eyes are not actually focussing on the mirror itself, they are focussing on whatever is being reflected BY the mirror.

If the mirror were not reflective, you would focus on IT instead.

If your mirror has any marks on it, you can focus on them instead and the image in the mirror would then become blurred.

I’m not describing this is scientifical terms :smiley: , but IIRC, it goes something like this:

If the Van Halen poster is 10’ from the mirror, it’s reflection is 10’ INTO the mirror. This phenomenom is how you can get an eye exam in a 15’x15’ doctor’s office. By reflecting the eye chart (or poster) in multiple mirrors, they replicate the distance needed to get a proper reading. When I was a kid, my eye doctor had an office capable of giving an eye chart reading from an actual 20 feet!

But it’s flat… Maybe I just don’t get the 10’ into part. A flat surface with depth kinda gives me the willies…

The light from a distant object is almost perfectly parallel. Your eyes are nearsighted, which means they cannot bring that parallel beam and focus it onto the retina. However, light from a nearby object is diverging at a large angle, which your eyes can focus. You can also put a concave lens in front of your eye which changes a parallel beam into a diverging beam - that’s why your glasses allow you to see distant objects sharply.

When a parallel beam is reflected by a flat mirror, it’s still a parallel beam. The effective distance to the image doesn’t change, and you still can’t see it sharply. But a convex mirror should allow you to see farther without your glasses.

So - I’m not looking at the mirror - I’m looking at parallel beams reflected off the mirror - but please, if you would, explain that part about the effective distance to the image doesn’t change. why not?

Aren’t our brains looking at a flat image and assigning depth based on our knowledge of our surroundings/adaptation? How can a mirror display depth when it’s flat?

I am slightly nearsighted, not enough to need glasses. I have very very good close-range vision, better than most people I know. I have crap long-range vision when it comes to reading.
So I have a question - are near sighted people always very good at close-range seeing?

Try searching for ‘how do mirrors work’ on the net.

This is one of several sites…


Hope it works.

Try searching here. Cecil on Why does a mirror image look fuzzy to a nearsighted person, even if the mirror is close?

OK, how about this? Suppose you have a room with a mirror on the wall. You look into the mirror, and see what appears to be another room on the other side of the wall. OK, let’s try that. Take the mirror away, and replace it with a window into another room. What you see in that window should look just like what you see in the mirror. If what you see in the real room beyond the window looks blurry, then what you see in the reflected room beyond the mirror should also look blurry.

If you have a camera with manually controllable focus (an SLR for instance), you can rig up a pretty simple little experiment/example. I’m sure you can figure out what I mean, and I don’t really want to type a whole lot here.

I’m very near-sighted. I can’t say that my close-range vision is any better than average.

I’m highly nearsighted and I can frequently read microprint on currencies and checks and other documents. But that’s really neither here nor there in terms of the OP (which, given how often threads diverge around here, means precisely dick).

I meant that a flat mirror doesn’t change the divergence of the beam. To the eye, light directly from a distant star looks the same as the light from that star reflected by a flat mirror - both are perfectly parallel beams. In each case the distance to the “image” (direct or reflected image) is infinity. The two are indistinguishable. You might say that a mirror can recreate the incoming light with all the information preserved, including all the cues needed to determine distance. Just like a hologram.

Refraction, the proces by which the cornea and lens focus light on the retina, is not affected by linear distance from the light source but by the angle of incidence of the light. In a perfect mirror, the angle of incidence of the light from a virtual image in the mirror is the same as for light from an object at that whole distance apart.

Myopia is a physical refractive/eyeball geometry condition. Eyeglasses work by changing the angles of incoming light so that they are at the right incidence for yuur eye to focus on them properly.

If you stand two feet from a mirror and look at the reflection of something 10 feet behind you the image has to travel 10 feet to the mirror then 2 more feet to get to your eyes so it’s like looking at something 12 feet away.

Putting this another way - think about replacing the mirror with a picture of the same scene. You would be able to focus on the picture (which is a short distance in front of you), where you can’t focus on the actual objects (whose light is reflected in the mirror). Think about how far the rays of light are traveling from the original source: from the picture, a short distance (it’s the source); from the objects seen in the mirror, a longer distance - the distance from the object to the mirror, where the light reflects, then the distance from the mirror to your eyes.

My opinion on optics in general is that these types of questions are very clear when you see a diagram, but are hard to explain verbally without one.