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?
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.