Does anyone have tips on blocking high power uncut lenses to get around parallax errors on a blocking machine? Also the thickness from it sitting on the holders and the angle of block placement sometimes result in PD's and heights being off.
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Does anyone have tips on blocking high power uncut lenses to get around parallax errors on a blocking machine? Also the thickness from it sitting on the holders and the angle of block placement sometimes result in PD's and heights being off.
Get yourself some Plano prisms and lay them on the concave side of the lens you are blocking to neutralize the effect of the prism in the lens. This is if you are blocking concave side up. The lens being tilted will only happen if you block convex side up not much you can do to fix that except to measure the error and er reblock to compensate for the error.
What type of blocker / edger set up do you have?
Geometric center blocking works best and set edger to decenter. Bevel placement is greatly improved. Where it gets tricky is making sure block and chuck will not be damaged. If decentration is excessive this may not be an option.
We use 7E's using this method with great results on lenticular / strong plus lenses
Thanks all. I like the idea of placing plano prism to neutralize the effect. Just need to have a bunch of high prism lenses made now... Also how do you align everything perfectly seems like quite a hassle.
We do GC blocking with concave up. Another challenge is keeping the block on with high plus or lenticular lenses :s. Do you guys used curved blocks for that?
Yes flex half eye blocks
Precision Tool Tech Optical Products 2018
pg 46
You only need a few prisms like 2 4 6 you don’t have neutralize the prism completely 2 or 3 diop remaining should not cause a problem.