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Contact lenses, focal length and uncorrected far point distance

  1. Nov 4, 2009 #1
    1. A nearsighted person wears contacts with a focal length of -7.6cm. If this person's far point distance with her glasses is 8.7m, what is her uncorrected far point distance?



    2. 1/F=1/do+1/di



    3. 1/-7.6=1/do+1/870
    =-7.534


    I am completely lost here...please help. Thanks!
     
  2. jcsd
  3. Nov 5, 2009 #2
    Re: Optics

    So it's not just me then...
     
  4. Nov 5, 2009 #3

    mgb_phys

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    Science Advisor
    Homework Helper

    Re: Optics

    The image distance is constant in both cases (the length of the eyeball)
    You have an unknown focal length lens (the eye) and a combintion of the same unknown lens and a known lens with a known object distance.

    So write the equations for object, image distance and focal length for both cases.
     
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