Originally Posted by
MakeOptics
Chromatic Aberration, you effectively neutralize it when you place your prism in the lensmeter. If the lens has no prism thinning the the optical center is ground at the prism reference point, if your progressive is on average 4mm above this point at fit and the distance reference point is another 3mm to 4mm above that point, then you are a total of 7mm to 8mm off axis and will experience some prism. If prism thinning is included again using some assumptions lets say a 2.00 add, the amount of prism thinning is going to be roughly 2/3 or 1.33^D and the orientation is going to be base down, on a plus lens you are going to be 7mm to 8mm off axis and add that additional 1.33^D you would compound the issue.
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