Frame with single + 0.125 lens. This is the smallest correction the human eye can distinguish.
Generally, eye doctors specify lens prescriptions to the nearest 0.25 diopter, so test lens sets are made in 0.25 diopter increments. However, if you are going to look at a precise distance, and pay close attention, most human eyes can distinguish steps as small as 0.125 diopters.
Use this 0.125 diopter lens in combination with a standard test lens set, or a test lens frame (sold separately) to fine tune your preferred lens strength, by adding it to one of the other lenses.
Lens diopter powers are additive, so if you determine that a +0.50 seems to work best, but you want to fine tune, you can look through the +0.50 and the +0.125 together to get an effective +0.625 lens, to see a half step up, or you can look through the +0.25 and the +0.125 to see an effective +0.375, a half step down.
The math for negative power lenses is the same. A -0.50 lens plus a +0.125 lens will give you an effective -0.375 diopter lens.
A 0.125 diopter lens costs $ 5, when ordered as part of a test lens set, or a test lens frame, or $10 if ordered separately. Shipping included inside the US.
Note, these are not tempered or impact resistant glass, and could shatter if struck, causing injury, blindness, or death. These lenses should not be used for actual shooting, or as a replacement for safety glasses.
These lenses are not a substitute for professional eye care. If you suspect you have a vision problem, you should always consult a professional.
