True CR-39 should never be used for rimless glasses. As for semi-rimless, it is perfectly fine, as long as the semi-rimless style does not need holes drilled in the lenses, which is most of them these days.
True CR-39 has an index of 1.49 (sometimes rounded off to 1.5 by some vendors). If you see any other index, 1.56 for instance, then it is not a *true* CR-39 lens. CR-39 is a brittle material that does not hold up well to stress, and can fracture while being drilled, or at drill points later on due to invisible micro-fractures caused by the drill. I've always been curious if using a Flo-jet (water jet drill) would be better for this, as it would be less likely to cause the micro-fractures at the drill point. Polycarbonate is the material most widely used in rimless glasses, but that does not make it the best choice, just the cheapest. Poly has a horrible ABBE value, which can cause all kinds of optical problems, especially the higher the Rx goes. Many people cannot wear poly, even at low powers, due to the poor optical quality of the lens. For those reasons, many are choosing Trivex for rimless glasses, or Seiko 1.67 mr-8 for higher index lenses. -=# Firewalker #=- On Jun 4, 3:38 pm, TujuMaster <[email protected]> wrote: > I hope this has not been asked before but I searched the group and > found nothing on this. I was talking to a friend of mine and he says > Polycarb lenses should always be put in rimless and semi-rimless > glasses. Since I started wearing glasses six months ago, I purchased > two pairs of rimless specs, one with CR39 1.5 index and CR39 1.56 > index, and a pair of semi-rimless CR39 with 1.5 index. Is CR39 not > recommended for these types? Does it shatter to easily? I've never > had an issue with CR39 and I'm pretty rough on my specs. Your help is > greatly appreciated. --~--~---------~--~----~------------~-------~--~----~ Check us out at the oft-updated http://glassyeyes.blogspot.com! You received this message because you are subscribed to the Google Groups "GlassyEyes" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/glassyeyes?hl=en -~----------~----~----~----~------~----~------~--~---
