Originally Posted by
sharpstick777
The fundamental issue with pre-cast blanks and adds is that they are dumb. It doesn't know the RX that is going into it, it doesn't know the frame shape or size, it doesn't know what is going into the other eye, or the POW measurements. With True 100% free-form all those become factors in a good design.
As well, aligning two corrective surfaces becomes more tricky. make two circles with your hands, and look through both at the same time in row. Fine, you can see ok, but now walk around. With dual surface designs you are aligning 3 things, the eye and two lenses. With single surface designs you only have to align one lens and one eye. It vastly reduces the chances of something going wrong.
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