Measuring the four paraxial lens parameters using an autostigmatic microscope

We describe a method of measuring the four paraxial lens parameters-the two radii, the center thickness, and the index-of a realistic-size positive lens using an autostigmatic microscope (ASM). The method is similar to measuring the radius of curvature of a concave mirror with an ASM but slightly more complex in that four characteristic distances must be measured to solve for the four unknown parameters. Once the four distances are measured, it is shown how to use an Excel spreadsheet and the add-in iterative "Solver" to find the four unknown parameters. Finding the paraxial lens parameters is useful for troubleshooting a lens assembly that does not perform as expected due to mislabeling, the incorrect glass type used, insertion into the assembly backward, or for finding a replacement glass type.