Quote Originally Posted by ml43 View Post
Sorry for the confusion, when you said franklin bofocal, I assumed you meant executive bifocal(old habits die hard).


you don't need to surface anything to prove the math.

Easiest way is to take two FSV lenses with opposing powers(i.e. +1.00 ds and -1.00 ds)

Put them back to back, total power of plano.
If you moved them together in a lensmeter there should be no prism induced.
But if you move one separately from another, it will behave like a +/- 1.00 DS in terms of prism
Ok that makes sense, I will have to play with that on Monday, so for arguments sake I will grab a -2.00, plano, +2.00, and for kicks and giggles a +4.00 and use these for the distance Rx. I will also grab a +2.50 for my super imposed add and in order to get 2 diopters of base in prism I will need to move the +2.50 lens 8mm for each example?