Al -

I guess I should be glad to find that I'm not too old to learn a bit of new stuff.

As Q reports, Product Information: PPG CR39 reveals that CR39 is a "CR-39 allyl diglycol carbonate monomer," so previous information I received from suppliers, that it was an acrylic, was incorrect. This brief page is careful to distinguish this carbonate from polycarbonate that is, I think, what suppliers I've talked to who refer to their lenses as "carbonate" or "polycarbonate" are talking about.

"Lenses from CR-39 monomer give less chromatic aberration as measured by Abbe number than polycarbonate lenses."

At the left of the page there's a link to "other materials" that may be of interest. The "Product Bulletins" are all .pdf, but the MSDS sheets are html. There are several references to "polycarbonate" being an inferior material, but nothing to say what "polycarbonate" actually is. Apparently PPG doesn't sell it.

Possibly also of peripheral interest: PPG Optical Products History gets a short (107 KB) history, indicating that PPG is the patent holder for CR-39, and it's been around since 1940. This is well before the appearance of "polycarbonates" so far as I know, but I haven't been able to confirm that.

In addition to the misinformation on their "acrylic" lenses, I have to suspect that the competitors who offered polycarbonate lenses were similarly uninformed. I haven't found any good properties on optical polycarbonates, but advertising seems to indicate that it's customary to always apply a hard coating, when the lens blanks are produced, so since the vendors don't get to charge extra for it they didn't know it was there(?).

More research to do...., but the CR39 "name" was really helpful getting to better info than I was able to find the last time I searched.

John