Because it sure seems to melt when heat is applied.
I crazed the daylights out of a lens (AR-coated) by heating the bridge (and I used that "concentrator" thing on my hot air blower). That's an expensive mistake.
Is this commonplace?
Because it sure seems to melt when heat is applied.
I crazed the daylights out of a lens (AR-coated) by heating the bridge (and I used that "concentrator" thing on my hot air blower). That's an expensive mistake.
Is this commonplace?
I never heat a bridge with lenses inserted if it can at all be helped. Any lens. Doubly so if it's not one of mine. Just seems to save a lot of potential issues. And of course, most zyls are only seconds to pop the lenses out, and back in again anyway.
Ha. No, it was one of mine.
I am making a "remove all high index lenses before heating frame" rule, for our jobs.
Maybe it should be "remove all lenses before heating frame" for outside jobs, 'cause you never know?
Remove them all, I do on any zyl frame no matter if the lens is coated or not.
Roy W. Jackson, Sr. ABOC
It's (usually) so super simple with most zyls, and then there is zero risk of heat crazing.
High heat + almost any treated lens = Certain doooooooooom!
Sorry...the Halloween spirit got me a bit carried away there. ;)
Pulling out the lenses and inserting demolens is a solution but not ideal. The lens finally determines the shape of the whole frame to some extent. I made a heat shield for the lens mounted in the frame so that you can easily heat the bridge and so far I have not had problems with cracking the coating. When bending the frame you just have to be careful that as a result of the binding of the frame-lens the coating does not crack.
First thing to understand is the expansion/contraction ratio of materials.
SiO2 is the AR stack. SiO2 is Silica DiOxide. Silica DiOxide is glass, in a nut shell.
Every material will have its own expansion /contraction ratio. When these differ, crazing will occur. Period. It is physics.
167 will always craze when heat is applied
CR39 will craze over time. Don't believe me? Leave a CR39 in a car in summer and see what happens.
Trivex will craze over time, but only with excessive heat
Poly, believe it or not, is the best material (other than glass) in terms of AR compatibility vs heat.
Though not ideal, remove the lens prior to heating acetates. Or do like myself and others, create your own custom heat shields.
Even the best thermal and primer coated, multi-$ top shelf, U can't touch this, I need a second mortgage, coatings will craze under these conditions. Every. Single. One. It's just a matter of time, and it will be on you, not the lab, if you continue to overheat frames with lenses still glazed.
I bend light. That is what I do.
I always pop my lenses before heating a zyl frame .
That heat shield sounds like nifty device.
I use painters tape (also used for occlusion and matching fitting heights) with a spot hot air blower.
WRT the lens shape effecting the let-back or set-back temple angles after adjustment and reinsertion, I'll over or under-correct with the lenses out, then tape and tweak with localized hot air.
However, removing the lens is risky business on old acetate frames- avoidance is almost always best.
Best regards,
Robert Martellaro
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
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