One of the challenges of the optical manufacturer is measuring a lens curvature and its radius. Producing a lens has a long process from the raw material stage until the final product is created, which is polished and curved, either spherical or aspherical.
Measuring a polished and transparent flat lens is possible, albeit challenging. Measuring a polished and transparent lens which is curved is even more challenging since the signal back-reflection has to go inside the detector in order to get a measurement. The angular coverage of a laser sensor over glass is very limited and stands over a few degrees only.
Along the lens manufacturing process there is a stage where the lens is still diffusive after its grinding, and before polished. Such condition is perfectly suitable for measuring by a non-contact laser sensor. Other technologies which are also used today are manual spherometer and a touch probe. Both are relatively slow process and a non-contact sensor can make the measurement much faster.
In order to get good results we decided to make a high resolution scan using a 25mm lens and short stand-off distance. By comparing the Optimet non-contact sensor to a touch probe we see that the main advantage of the Optimet sensor is the ability of measuring the entire lens at high speed obtaining a full 3D scan of the surface. The Touch probe measures only one profile at a time and it needs a new setup adjustment for each individual scan.
Optimet’s sensor was able to measure the radii with a fractional error of <0.2% for the convex surface (short radius) and 0.07% for the plano-concave surface (long radius) when compared to the touch probe results.
For more information please read: diffusive lenses radii measurement application report.