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Basic question concerning mirrors

  1. Oct 21, 2009 #1
    Hello all.
    First off, i would like to apologize for having to ask this question on a physics forum. As you will soon see, i know next to nothing about physics, but this is a question that's been troubling me for years, and i've never found an answer to it. So hopefully one of you good people can give me a quick answer, and i'll leave you to do your thing!
    Sorry if i picked the wrong forum.

    So hear goes...

    It's my understanding that when i look into a mirror, i'm having light reflected to me from a 2-dimensional surface. Yet, when i look at myself in the mirror, the background gets blurred and out of focus, just like it does when i look at objects in the real world. I look at the background and i become out of focus and blurred.

    What's going on here? How does a 2-dimensional image have 3-dimensional depth?

    I don't consider myself a stupid person, but this really does baffle me. So yes, i know absolutely nothing about physics. Laugh or don't laugh, help or don't help, but it's a question i had to ask. Thanks to anyone who can answer this for me.
  2. jcsd
  3. Oct 21, 2009 #2


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    A mirror is not a tv-screen. The picture in the mirror in not on the mirror's surface. When your eyes focus on things in the mirror, they don't adjust to the distance eye<->mirror but the distance eye<->mirror + mirror<->object. To understand why it is so, you need to understand how seeing, focusing and reflection works. Draw some diagrams then.
  4. Oct 21, 2009 #3
    The light does reflect from a two dimensional surface but the reflected rays diverge and you see each image point not at the point on the object where the rays actually come from but at the point where they seem to come from this being as far behind the mirror as the object is in front of the mirror.
  5. Oct 22, 2009 #4
    Thanks guys. Appreciated.

    I do realise that the light comes off the mirror at different angles, relatave to the source, and even realised that we have to focus through the mirror, rather than on it. Though i still can't get my head around why we are able to focus through it. I would've thought a point of light has to get to a point in my eye, regardless of it's angle, but it seems i'm looking at this all wrong.
    Looks like my issue is with the focusing side of things. So reading up on that will be my next task when i got some free time. Don't worry, i won't be bugging you guys with that! I'm actually a musician, so it isn't exactly high on my priority list.

    Well thanks again. You were both a help.
  6. Oct 22, 2009 #5


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