Re: New lenses have high chromatic aberation Ugh!

"Mark A" <nobody@xxxxxxxxxxx> wrote in message
news:A7qdnSJJL8aPQkvenZ2dnUVZ_tGdnZ2d@xxxxxxxxxxxxxx
> "JohnR66" <nospam@xxxxxxx> wrote in message
> news:VDyBf.536668$zb5.71660@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>I have a very strong prescription. -15 range with astigmatism. I ask for
>>the best in plastic lenses. I get high index aspheric with abrasion and
>>reflection coatings. They always had strong off axis chromatic aberration.
>>A year ago, what I got was incredible. Virtually no chromatic aberration.
>>I could look out near the edge and still read the fine text on my screen.
>>
>> The coating was getting scratched so I ordered new lenses. These are
>> nasty. Lots of color smear like the older ones. What baffles me is the
>> optician tells me the same material was specified. She tries to adjust
>> them and finally to no avail (I knew it would not make a difference).
>> Clearly this can not be the same material. I guess the lab may have used
>> low dispersion material before.
>>
>> The optician tells me the lab used both times is Hoya. Can someone tell
>> me what the low dispersion material is? What is the index and Abbe
>> numbers? IIRC, the optician says the material they specified has an index
>> of around 1.6
>>
>> Thanks for the help. John
>>
>
> It may be polycarbonate, which is 1.59 index, although I don't know of any
> polycarb lenses that go to -15.. Polycarb has the lowest abbe value (30)
> of any widely used material and is even lower than most 1.70 index
> materials. The advantage of polycarb is that it has high impact resistance
> and high tensile strength. Otherwise it is crap.
>
> Hoya, like other manufacturers, have lenses in many different materials,
> so you need to find out exactly what it is.
>
Mark,
I've been poking around the Web tonight and from what I found, It seems the
good lenses may be Spectralite. They are a couple mm thicker than the ones I
have with the color fringing. I think the lower index with higher Abbe
should give me better vision from what I read. I guess the curving
distortion will be reduced as well. I read that CR-39 is ideal, but would be
very thick and not available in my Rx.

Thanks, John


.

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