Originally Posted by
Barry Santini
And I've found that the typical trigonometric calculations for figuring how to compensate (outwardly)the PD with witch to block a wrap are...WRONG (or at least inaccurate).
In frustration, I decided that, as a visual learner, I needed to see this wrap-narrowing phenomenon in action in order to get my brain around it. So I decided that I needed to get a wrap-adjustable frame, i.e., a *folding* frame. So I ordered an new (old?) Persol folding, zyl aviator sunglass. I played around by putting in clear lenses, marking PDs (say 27, 30 & 35) and then adjusting the wrap angle of the frame to 15, 20 & 25 degrees,and this is what I've found:
ALL THE CALUCULATORS OVER-ESTIMATE THE AMOUNT OF *NARROWING* THAT OCCURS.
For example, for a 20 degree wrap angle, the standard formula says spread the mon-blocking PD by almost 2 mm...but I found that 0.5mm (at a 35PD) worked just fine.
Why, I don't completely understand...yet!
But, like the wright brothers, I'm ready to question what I've been led to believe to get better answers.
Any Ideas?
Barry