Use this simple tool to solve physics problem related to thin lenses. You can use this tool find focal length for thin lens by giving lens radii and index of refraction of the material this lens made of. Please remember to use correct sign convention when you enter radii.
Sign convention of lens radii R1 and R2
The signs of the lens radii indicate whether the corresponding surfaces are convex (R > 0, bulging outwards from the lens) or concave (R < 0, depressed into the lens). If R is infinite, the surface is flat, or has zero curvature, and is said to be planar.
Type of lenses
Using lensmaker's equation for thin lens, we can find focal length for lens