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Homework Help: Simple thinking problem - mirror refraction

  1. Mar 9, 2005 #1
    Suppose you want to take a photograph of yourself as you look at your image in a flat mirror 1.8 m away. For what distance should the camera lens be focused?

    You must be ½ the total distance away: since the angle of incidence is equal to the angle of reflection, the distance needed to get a full view is ½ the total distance.

    1.8 / 2 = .9 m

    seems to easy. Is that right? :bugeye:
  2. jcsd
  3. Mar 9, 2005 #2

    Doc Al

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    Staff: Mentor

    No. Instead, ask yourself: how far away from you is your image in the mirror? That's the distance you need to focus the camera. (The camera, like your eye, knows nothing about mirrors. If the object (in this case, your image) looks 10 feet away, then you need to focus for 10 feet.)

    (Hint: The image in a plane mirror is the same distance behind the mirror as the object is in front of the mirror.)
  4. Mar 9, 2005 #3

    okay, I'm thinking it's just 1.8 m, but still to easy.

    You're hint is kinda throwing me off. heh. but then it sounds like it should be 1.8 since I am only 1.8 m away and thus camera lens needs to be 1.8 m away since it acts in accordance w/me eye.

  5. Mar 9, 2005 #4
    Look at his hint more closely...He says The image in a plane mirror is the same distance behind the mirror as in front....so think about it.
  6. Mar 9, 2005 #5
    okay then obviously there is no distance this is simply the mirror of the distance of the object.?
  7. Mar 9, 2005 #6
    No...Pictures are made after light is exposed to film...Take one piece of light as follow it in your mind the distance from the film to the mirror...reflected...and back to the film.....what is the distance?
  8. Mar 9, 2005 #7
    twice the distance. ?
    Last edited: Mar 9, 2005
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