You might be confusing CR-39 plastic lenses with other MR type plastic lenses. CR-39 only comes in an index of 1.498, however many lens manufacturers produce lenses they might call CR-39 that can have slightly different indices. I can be easily argued that the difference between 1.498, 1.5 and 1.56 index lenses will be indescernable - the lens size, shape and lab work will be much larger factors.
Now, to your question about drill mounting CR-39; there seems to be conflicting opinions on this within the dispensing industry. Some say that CR-39 will crack or chip if drill mounted, others have said that they've drill-mounted CR-39 for years with few problems. There seems to be a conflict here with 'newer' polycarbonate lens propaganda clashing with more 'traditional' CR-39 lens history, with the trend moving everyone to the newer and more expensive option. For example, our local Lens Crafters refuses to do drill mount frames with anything but Poly - and their dispensers gasp if you mention anything else. It's what they've been told is the only option and they scare their customers into believing that their eyes might be at risk unless they pay for Poly. I would conclude with this; 1. Don't be worried that your CR-39 lenses are more likely to shatter than polycarbonate - they're both very highly impact resistant. 2. If you are happy with your current lenses, you should stick with them, especially if they're inexpensive. 3. Understand that there are always newer materials out there, like Trivex, which by comparison is lighter and stronger than CR-39, but it's also more expensive - you can experiment with other options if you choose. J. Evan On Jun 4, 9:38 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 -~----------~----~----~----~------~----~------~--~---
