posted by Cole .
A planoconvex lens is to have a focal length of 28.5 cm. If made from fused quartz, what must be the radius of curvature of the convex surface?
Use the so-called "lens maker's formula" and an index of refraction of N = 1.458 for fused quartz.
1/f = (N-1)/R1 (for a plano-convex lens with R2 = infinity on one side)
Solve for R1.