Abbe Value High Index Lenses
Wondering what the aberration is going to be like in your 1.67 high index lenses?
High Index Lenses and Abbe Value
The Abbe value on a lens affects its clarity, and if you’re interested in getting a pair of glasses with high index lenses, Abbe value and clarity are things worth considering.
The reason is that, as your refractive index goes up (high index lenses simply have higher refractive indexes than standard plastic or glass lenses do), your Abbe value generally goes down. As Abbe value goes down, aberration goes up. As aberration goes up, clarity goes down. Confusing, right? Let’s break this down.
The refractive index of a lens describes its efficiency at bending light. Imagine that you have a small crystal and a drop of water. They’re similar sizes, but light acts very differently when passing through each one. If light passes through the glass at an angle, it’s going to come out at a slightly different angle than it came in at. Light going into the crystal at the same angle will come out at a wildly different angle, however. This is because the crystal is more efficient at bending light.
What do prescription lenses do, anyway? They bend light. Your prescription lenses alter the way you see the world by altering the way light reaches your eyes. The more efficiently your lenses do that, the thinner they can be. So, if we go back to the water vs. crystal analogy, if you took your prescription to the eye doctor and had a pair of glasses with water lenses and a pair of glasses with crystal lenses made, you’d see a huge difference in lens thickness. The crystal would be MUCH thinner, because it’s so much more efficient at bending light. This is because it has a higher refractive index (crystal is around 4, water is around 1.3). High index. You with me?
High index lenses tend to have lower Abbe values… which means more color distortion. Abbe value is essentially a number that tells you how much aberration a lens causes. The lower the Abbe value, the more aberration. WHAT DO ALL THESE WORDS MEAN?!
Aberration is what’s happening when a crystal breaks sunlight into rainbows. We like this when a crystal is hanging in the window. We don’t like it when our glasses do that to the light coming to our eyes. So let’s go back to our water lenses vs crystal lenses analogy. The water lenses are going to have a high Abbe value (around 73), which means they’ll have almost no aberration. So you’ll never see light turn into rainbows as it reaches your eyes. The crystal glasses, however, will have a very low Abbe value; something less than 10. This means that, while your lenses are very thin, you’ll notice that the edges of objects tend to seem to bleed colors. Edges and lines will have a certain amount of “rainbowing,” where their edges grow fuzzy, with colors seeming to bleed out from them.
Higher index lenses tend to have more aberration, which means they have more distortion. This is why you’ll sometimes hear about high index lenses having “lower clarity.” It’s because they have more of this “rainbowing,” or aberration. In other words, they have a lower Abbe value.
When shopping for high index lenses, you can assume that, the higher the index, the lower the Abbe value, and the more aberration you’ll have. In practice, most high index lenses do not have so much aberration that you’ll actually notice it. Where it starts to become an issue is when you get above high index 1.70. So, high index 1.74 has some noticeable but generally non-troublesome aberration. High index glass 1.80 and 1.90 lenses tend to have enough aberration to bother some people with very strong prescriptions. It’s a trade-off between clarity and thin, attractive lenses. You need to decide which is more important to you. We recommend going with high index plastic most of the time, as glass is more fragile in addition to its aberration qualities.
For more informative articles about high index lenses, check out our other posts. Leave a comment below with any questions you have or things you’d like to share!