Optical Clarity and High Index Lenses
The index of a lens is pretty much directly tied to its optical clarity.
If you are shopping for high index lenses and haven’t had them before, there are some things you should know about how the index of a lens can affect your vision.
Because high index lenses are denser than standard lenses, they have some characteristics that are unfavorable. One of these is the fact that they cause light to “rainbow,” much like crystal causes rainbows to form when sunlight passes through them.
Here are the things you need to know about how the index of your lens affects the clarity of your vision:
- The higher the index of your lens, the more dense it generally is. The lens’s density is related to its Abbe number, or the amount of aberration it causes.
- Aberration is when a lens “rainbows” light, just like a crystal splits sunlight into a rainbow. In a lens, this comes through as colors “bleeding” from the edges of objects, especially objects in your peripheral vision.
- Generally speaking, the higher the index of your lens, the more it will cause distortion. This is because higher index lenses are more dense than standard ones.
- High index glass has an especially low Abbe number, meaning this material causes the worst color aberration.
- Optical clarity is especially compromised if you have high index lenses with no anti-reflective coating. Anti-reflective, or AR, coating reduces the amount of light that a lens reflects. Since high index lenses are especially reflective, they need this coating. Otherwise, they cause a lot of distracting glare.
- Many people have no problem with the amount of color aberration they get from high index lenses. The people who notice it the most are those with very strong prescriptions and very high index lenses. Anybody with high index glass will notice at least some aberration.
- 1.70 high index plastic has a good balance between thinness, light weight, scratch resistance, and aberration. This is the best choice for most people.
High index lenses are thin, so the amount of distortion they cause is offset by the small amount of lens material that light passes through. The worst aberration occurs with very strong prescriptions (+/- 8.00 or more) and the highest indexes.
Most people get used to or never notice aberration, but it is a personal thing. Two people with the same lenses may have completely different feelings about how distracting it is. Regardless, it’s a good thing to be aware of if you’re getting ready to order high index lenses.
In general, the people with 1.70 high index plastic seem to find the least distortion and have the best overall experience with their lenses. We recommend this index for most people.
If you have any questions, browse our other posts or leave a comment below, and thanks for reading!
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