How do we measure center/edge thickness of a GP lens?

• A. Using caliper on the edge
• B. Using dial gauge (lens positioned on the gauge, plunger lowered onto the lens, and thickness read directly off the gauge)
• C. Visual estimation
• D. Reading thickness from a ruler

Answer: (B)

Measuring center and edge thickness with a dial thickness gauge gives a direct, precise readout of the actual distance between the lens surfaces at a defined point. By placing the lens on a flat reference surface and lowering a calibrated plunger onto the lens, the dial shows the thickness at that spot with high resolution. This approach minimizes distortion from handling or lens curvature and provides consistent measurements for both center and edge locations.

Calipers on the edge can deform the edge or only capture a single edge dimension, and don’t give a reliable center thickness. Visual estimation is too subjective and imprecise to detect small thickness differences. Reading thickness with a ruler lacks the calibration and fine resolution needed for GP lenses.