Originally Posted by
Darryl Meister
Craig, Can you specify the specific type of lens that you using? Is it a progressive lens? And, if so, is it a back-surface free-form lens (which generally wouldn't use an aspheric lens blank)?
Or by surfacing a "blend" with a "digital machine," do you mean the round bifocal seg option that some free-form software packages offer?
And is 1.60 or 1.67 high-index not available in the lens type that you are using? Both are excellent lens materials for drill-mounts.
In any case, for a back-surface free-form lens, the "add power" measured by a focimeter is very nearly equal to the difference in surface power readings between the distance and near zones of the lens, as you might measure with a lens clock (compensating for refractive index, of course).
For such lenses, you will probably not be able to simply "calculate" these surface powers in advance though, since these calculations are rather complex and typically handled by the free-form surfacing software.
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