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Medical Forum / General / Vision / October 2007CR39
Are most basic plastic lenses made of CR39, or is there another basic plastic that's significantly thicker? I've just bought some glasses and I think the lenses are polycarbonate because the chromatic aberration is quite severe and they're definitely thinner than my old glasses (even though the new frame is larger you can still see a clear difference at the edges) which have Transitions from Dollond & Aitchison, made by Nikon I think. The optician I ordered them from seems to think they're CR39 though.  SignatureTH * http://www.realh.co.uk > Are most basic plastic lenses made of CR39, or is there another basic > plastic that's significantly thicker? I've just bought some glasses and [quoted text clipped - 7 lines] > -- > TH *http://www.realh.co.uk its hard to know for certain but polycarbonate is known for high chromatic aberrations and it's higher refractive index does result in the lenses being thinner. Nikon does indeed make photochromic polycarbonate lenses and most optical shops like to use them because they are more profitable for them so I suspect that your suspicion is correct. an experienced optician can listen to the sound of the lens tapping against a hard surface and distinguish plastic versus polycarbonate. the optician you ordered them from would know *exactly* what they are made of unless he/she is trying to be deceptive. > > Are most basic plastic lenses made of CR39, or is there another > > basic plastic that's significantly thicker? I've just bought some [quoted text clipped - 17 lines] > the optician you ordered them from would know *exactly* what they are > made of unless he/she is trying to be deceptive. You've got the wrong end of the stick a bit. My current glasses are Nikon Transitions - "Basix" I think they're called - but they're not polycarbonate, they're thicker plastic (CR39)? They did make them with polycarbonate at first but I got them remade with plastic when I found I couldn't see properly. I wanted a second pair that aren't Transitions because in Winter I want to take advantage of every little scrap of sun, not have it blocked out, so I ordered some cheap ones online, expecting them to be plain plastic, but I'm sure they're not. Funnily enough their address turned out to be local but they say that's only a dispatch centre and I can't call in there. That could sound suspicious, but I still think it's a mistake rather than deception. Polycarbonate lenses aren't actually cheaper to make than CR39, are they? Just a higher profit margin because they usually charge more for them, which this optician hasn't done. SignatureTH * http://www.realh.co.uk > Polycarbonate lenses aren't actually cheaper to > make than CR39, are they? Just a higher profit margin because they > usually charge more for them, which this optician hasn't done. Polycarb material is more expensive than CR-39, but it could conceivably cost more to stock CR-39 in all lens powers (finished) or all base curses (unfinished) if the demand is low. > In 1193595686.296473.184...@d55g2000hsg.googlegroups.com > [quoted text clipped - 39 lines] > -- > TH *http://www.realh.co.uk at the optical location I am the doctor at, we charge the same for polycarb and plastic lenses but we make a higher margin on polycarb so the optical staff tends to over-recommend it. I don't know if lower manufacturing costs are the cause of the higher margin on polycarb. or not. > at the optical location I am the doctor at, we charge the same for > polycarb and plastic lenses but we make a higher margin on polycarb so > the optical staff tends to over-recommend it. I don't know if lower > manufacturing costs are the cause of the higher margin on polycarb. or > not. Plastic? Do you mean CR-39 (1.50 index) or some other index such as 1.60 or 1.67? > <p.clar...@gmail.com> wrote in message > [quoted text clipped - 8 lines] > Plastic? Do you mean CR-39 (1.50 index) or some other index such as 1.60 or > 1.67? CR-39. >at the optical location I am the doctor at, we charge the same for >polycarb and plastic lenses but we make a higher margin on polycarb so >the optical staff tends to over-recommend it. I don't know if lower >manufacturing costs are the cause of the higher margin on polycarb. or >not. The three labs that I work with charge more for spherical polycarbonate than they do for spherical front surface scratch resistant cr39. Just to be sure, I pulled the price lists from a half a dozen other labs and they all show higher prices for poly, some by as much as 50%. Are you in the US? Is your lab owned by Essilor? (Essilor owns Gentex, a major supplier of poly blanks). Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman
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