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by kps
2465 days ago
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Higher index lenses tend to have greater chromatic abberation. https://en.wikipedia.org/wiki/File:Abbe-diagram_2.svg In practice different materials of the same index can have significantly different abberation. When I very recently got work-optimized glasses from a local optician, I could sit down and compare the materials they could get. One of the 1.60 index materials (Hoya, I think) was as good as thicker lenses while another (Essilor?) would have given me noticeable fringing on a monitor. Now try to get a place like Zenni to so much as tell you what they're selling. |
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The general trend is that higher-index materials tend to have lower Abbe numbers, but there are exceptions. Polycarbonate is a cheap and popular mid-index material that's widely recommended on the basis of its mechanical strength. Its index of refraction is 1.59 and its Abbe number is 30, but there are numerous materials with a similar index of refraction around 1.6 and substantially better Abbe numbers of 41-42, or materials with a significantly higher index of refraction (1.67) and Abbe numbers that are slightly better than polycarbonate.
Zenni and EyeBuyDirect don't want to promote awareness of chromatic abberation, but they do make it easy to know whether you're ordering polycarbonate, and they both have 1/6/1.61 index materials with better Abbe numbers than polycarbonate. Zenni uses one of the Mitsui MR materials for their 1.6 lenses.