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I have a convex lens, and I want to calculate it´s radius of curvature. It´s focal length is 24cm. how do I do it?

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  • $\begingroup$ You need to find out what it's made of (or otherwise find its refractive index out) then use the lensmaker's equation. $\endgroup$ – WetSavannaAnimal Jun 20 '17 at 13:36
  • $\begingroup$ The lens is made out of glass (I took it out from a magnifiyng glass). What is the lensmaker´s equation? $\endgroup$ – Jlopez20 Jun 20 '17 at 13:40
  • $\begingroup$ There are heaps of different lens glasses of vastly different indices. If you want a hazard a guess, go with Borofloat, soda glass or N-BK7. All of which have $n\approx1.5$. $\endgroup$ – WetSavannaAnimal Jun 20 '17 at 13:43
  • $\begingroup$ Ok, then what is the lensmaker´s equation, and how do I use it? $\endgroup$ – Jlopez20 Jun 20 '17 at 13:48
  • $\begingroup$ This is the lensmaker's equation $\endgroup$ – John Rennie Jun 20 '17 at 15:34
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You could also stand the lens on edge on a table (next to a ruler for scale), take a birds-eye view picture of it, print out the picture, and use a compass to draw a circle with the same radius as the image of the lens surface. Then scale your result based on the scale of your printout.

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