Sometimes we get lenses for analysis with no documentation. We can usually make a good guess at the index, but I would like to know the best way to determine it more accurately.
Ways I have tried are: 1/ to physically measure the curvatures, and use the accurate lens making formula to fit a focimeter reading by adjusting the index value,
2/ work backwards from the reflectivity as measured by a spectrophotometer.
Method 1/ is difficult if the surfaces are not just combinations of spheres and cylinders, while method 2/ is complicated by the presences of coatings and the insensitivity and unrepeatability of the measurements.
Does anyone have any suggestions to make life easier please?
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