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Question about sign convention for R1 and R2 when using the lens maker's formula

  1. Mar 28, 2012 #1
    Hi!
    I'm having some trouble with optics.
    When we have convex, planoconvex, concave, planoconcave, and meniscus lenses, I don't understand how to substitute with the sign for R1 and R2. How do I determine whether the radius of a side is negative or positive? A book that I'm using said to take incident light in a particular direction and then measure the radius from the lens itself, but I honestly still don't understand that method at all... Then I found this:

    http://www.livephysics.com/tools/optics/focal-length-for-thin-lens.html

    but even though it says there that a surface "bulging out" of the lens is taken as R>0, and a surface "depressed into the lens" is R<0, it has the exact opposite shown in a few of the diagrams..

    I'm confused and I would really appreciate it if someone could clarify this.
    Thank you!
     
  2. jcsd
  3. Mar 29, 2012 #2
    Use sign convention. For example R1 is negative if it lies on ghe left side of the pole.
     
  4. Mar 30, 2012 #3
    It makes sense now! Thank you!
     
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