> My insurance can cover some of the cost of these lenses, but they are
> still expensive.
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> clarity-wise? With regards to the Abbe value? I have 1.64 "high
> index" now.
Most of the modern high end AR coating I mentioned (including the Zeiss
Carat Advantage) have a similar "easy to clean" surface. Early AR coatings
were very difficult to clean without leaving streaks (if you have an old
camera lens with AR coating you can attest to that).
Abbe value makes a big difference in the quality of lens (clarity is
probably not the best term for it, but it is not wrong either). I have never
heard of a 1.64 index lens (but not saying it does not exist). The common
lens indexes are below:
1.50 regular plastic
1.53 Trivex
1.59 polycarb (avoid this like the plague - lowest abbe value of any
commonly dispensed lens material)
1.60
1.66 or 1.67 (depends on lens manufacturer - some are 1.66 and some 1.67)
1.70
1.74
Normally, the higher the index, the lower the abbe value. The higher the
abbe value, the less chromatic aberration. The one exception is polycarb,
which has the lowest abbe value of any commonly dispensed lens. Abbe value
is more of an issue if you have a moderate to strong lens power. You may not
notice any difference between abbe values in a low power lens (plus or
minus).
Most lenses are polycarb (terrible optics, but high tensile strength and
high impact resistance) or 1.66/1.67. 1.60 is a good choice if you lenses
will not be too thick for you. Trivex is a good replacement for polycarb
were safety lenses are needed.
For the best advice on lens material, please post you exact Rx here. Also,
it would be good to get the exact manufacturer and lens design your optician
is suggesting for you (in addition to the lens material). Often times they
will not like to tell you (and some are so ignorant they don't even know),
but if they don't tell you, tell them you will take your business elsewhere.
SQ - 22 Jul 2008 22:46 GMT
> Normally, the higher the index, the lower the abbe value. The higher the
> abbe value, the less chromatic aberration. The one exception is polycarb,
> which has the lowest abbe value of any commonly dispensed lens. Abbe value
> is more of an issue if you have a moderate to strong lens power. You may not
> notice any difference between abbe values in a low power lens (plus or
> minus).
Interesting. Of course, I have 1.67 High-Index. I wonder if I should
go to 1.60 high-index versus 1.67 to get a higher quality lense, with
better view quality. Or is there not enough difference between 1.60
and 1.67?
My myopia is -5.25 Diopters in both eyes.
I want to get the best possible optical 'picture quality' and AR is a
step in the right direction towards that. I didn't specifically notice
that eliminated glare but did notice that it greatly improved view
quality in twilight and at night. This only became apparent when I got
a non-AR pair of lenses.
Also durability of AR coating is a huge issue for me. It's not that I
am rough with eyeglasses but I do tend to clean them several times per
day. A poor AR coating will scratch easy and come off eventually,
which is what happened to my previous pair of lenses. It did offer
nice view though.
Mark A - 22 Jul 2008 23:26 GMT
> Interesting. Of course, I have 1.67 High-Index. I wonder if I should
> go to 1.60 high-index versus 1.67 to get a higher quality lense, with
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> which is what happened to my previous pair of lenses. It did offer
> nice view though.
It is a mater of aesthetics and weight.
A 1.67 index lens is thinner and therefore lighter than a 1.60 index lens.
On a -5.25 this will show up as edge thickness, and is a cosmetic issue with
some people. But a lighter lens is also important to some people, and it
"could" keep your frames from slipping off your nose as much if the lens
where heavier.
But a 1.60 lens will have better optical quality than a 1.67 lens,
especially in terms of chromatic aberration (abbe value). Some people are
more susceptible to chromatic aberration than others.
Also, a 1.67 lens costs more, but sometimes it is hard to find a lens with
1.60 index material.
If you get one of the premium AR coatings put on by the lens manufacturer
that I already mentioned, I would not worry about AR durability.