You haven't, Clive. All of the lens manufactureres and their designers (and Darryl) are saying to fit at pupil centre. The vast majority of practitioners around the world fit at pupil centre and all textbooks say fit at pupil centre. I for one don't plan to second guess the experts. Also, as Darryl suggests, the focimeter (vert) is not human and does not perform in the same way as the human eye. That is why we have these little windows of simplicity on the progressive to satisfy the basic instrument.Originally Posted by Clive Noble
Among other things, the designers are considering the effects of aberrations, notably oblique astigmatism. If we don't fit how they suggest we will induce aberrations, albeit usually minimal. This is why we have to fit aspherics 1 mm below pupi for every 2 gergrees of pantoscopic tilt. many practitioners don't do that and their clients don't complain That doesn't mean they are getting the optimal result, though.
Regards
David
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