I bought some rimless glasses from an optician when I was in India earlier this month. The prescription says the lenses are LM Crizal - I've been asked if they're polycarbonate or plastic and I really don't know. The lenses are lenses are 3mm thick. Can anyone tell me from this description? And is Crizal the name of the lens manufacturer or the anti-reflective coating? Thanks.
Crizal is the Anti-Reflective coating. I do not know from your explanation if they are plastic or poly, but to tell the truth, I do not think it is anything to worry about.
To answer your question on; "is Crizal the Ar or the manufacturer?", Well, its kinda both. 'Crizal' is a brand name of Essilor. So to name Crizal, you have just informed the person you are dealing with that in fact it is Essilor the manufacturer of Crizal. Regarding the 3.0 thikness issue, well some questions need to be answered: 1. Is your Rx a "+" or "-" lens? If it is a plus power, then the center thickness will be thicker in the center than on the edges. If it is a minus lens then the center will be thinner than the edge. 2. Based on the previous statements, where was the thickness measurment taken, edge or center? 3. What, if possible to provide, is your prescription? 4. What kind of rimless, drilled or grooved? Again, this will also depend on the nature of your Rx. On plus power lenses, some thickness needs to be added so that the edges can withstand both grooving or drilling. Minus lenses usually have enough thickness to accomodate either mountings. 5. As to Poly or Plastic, it may be possible to answer that once we have determined some of the facts from the above questions.
These questions presented will assist in determining some of the major points you asked in your post. Also, the "LM" applied before "Crizal", I think that Pete Hanlin could better answer that question. It could simple be a trade mark for that region of the brand of Crizal, here again, I am uncertain as to that label.
I/we look forward to your reply so that I/we can better assist in your post.
:cheers:
Cowboy
Hit it with as small hammer, if doesn't break but scracthes pretty bad, it's poly. If it shatters, it's glass or CR-39.
That was funny, Chip!
Chip is still hammered from bike week!
Hi Cowboy - the prescription is -2.25 for both eyes, I guess they're drilled because the arms are fixed directly to the lenses and the 3mm is at the edge where the arms join the lenses.
Chip, that was a great one, one for the Comedy Stop! LOL
Melissa,
99.999% possitive that it is polycarbonate based on the fact that it is a drill mount. The -2.25, if you measured the thickness at the edge, it could very well be 3mm. this will also be determined by lens size. But, if it is a standard stock Essilor Airwear Crizal lens with a 1.5 center thickness and a 48mm lens size, the edge will be about 3mm thick. Another factor could be shape, the more angular, the thickness will be more apparent vs. round edges. Still uncertain about the "LM" thing though, where is Pete Hanlin when you need him!
:cheers:
Cowboy
Thanks Cowboy, they're rectangular-ish 47mm wide by about 27mm deep. They look pretty neat so I hope they're made of something strong like polycarbonate, don't want to break them!! I've seen some rimless that are so thin looking compared to mine though it's quite interesting to an amateur. Is it possible to tell how strong a lens is just by looking at it?
Here are several vague ways to tell
Polished edge - If the edges are clear, then they can be poly or plastic, but if they are white and unpolished then they are most likely plastic.
Finger tap test - If you tap the lens and you hear a slight echo, then it is poly, if it has no echo, then it is plastic. Very difficult unless you have one of each material to compare it to.
Not by looking at it, but I do a 'ping' test. I tap the lens with the rear of a pen. All materials have distinctive sounds. Poly has a highr pitch than palstic and so on. If indeed you have poly in your drill mounts and the holes were drilled correctly and the mounts are inserted correctly, you should have a well constructed pair. There are, of course, several factors that could cause a drill mounted pair not last, but we can save that for that circumstance and not jinx you now!
Have I/we on the optiboard answered your questions to satisfaction? If not, please ask away. If so, enjoy your new eyewear and any time you have a question about lenses, frames, or the eyecare industry, the optiboard is the place to get the answers.
Still looking for Pete Hanlin to answer the "LM" question....
:cheers:
Cowboy
Any good optician can tell how strong a lens is within at least 1/2 diopter just by looking at it. Exact measurement can be made by instruments and a few really good opticians can the strength of a lens without instruments with a supprising degree of accuracy.
In my younger days before I lost some feeling in my fingertips and when my job was making base curves for contact lenses, I could tell you the base curve of a contact within a 1/4 diopter, just feeling it with my finger tips.
Chip
Cowboy, those are sounds that we've all learned to recognize over time, I doubt that a lay person will be able to distinguish the sounds of each material.
Sorry.
Melissa, don't do the 'ping test'. It was was not intended to be an instruction, rather, an example of how I test for material differentiation. Instead, seek a good professional optician who can make a more possitive assessment on your eyewear. Clearly, we can only answer to the best of our ability based on written details. Tangible materials are much easier to assess and provide accurate information.
Cowboy
Thanks, I think you're all fantastic!!
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