A spherometer is a mechanical or optical measuring device featuring three fixed outer legs and a central movable plunger connected to a micrometer. By placing it on an optical surface and lowering the central pin until it touches, technicians measure the sagitta (depth of the curve). This measurement is then mathematically converted into the exact radius of curvature, which is critical for verifying lens specifications during fabrication.
Heard on the job
Grab the spherometer and check if this concave mirror actually has a 500-millimeter radius of curvature before we mount it.