I’ve been using some policarbonate glasses (Differentials and Normalized) since May, but I was struggling with the sensation of “unlearning” AF… very disappointing, of course. Then decided to order one of the cheapest contacts avaiable in Brazil to be used as differentials (both -5.25) at home. Best decision, AF is now easy-peasy!
Supposedly some people don’t see well through polycarbonate. It has a low abbe value compared to other materials, it’s lightweight and doesn’t shatter, but not great in terms of optical quality.
Polycarbonate is garbage. I can see very noticeable chromatic aberration (especially near a bright white/black edge) even with -1.25 sph polycarbonate lens, which is even more annoying when there’s transient astigmatism multiple vision on top of the actual chromatic aberration. The only good thing about them is their anti-shatter property, since many anti-reflective lens coatings will have anti-UV properties, making their anti-UV property useless.
If the lens power is small, just use CR-39. If it’s higher, then use Trivex or high-index plastic to get the highest possible Abbe number while having acceptable lens thickness, which is determined from the power (of the highest-powered axis if cyl is involved) and refractive index.
I wonder if a diamond lens is possible, since this site says diamond has 2.41 refractive index and 65 Abbe number, which should be even better than CR-39’s 1.5 index and 58 Abbe. But the listed “dispersion” is similar to polycarbonate, so it makes me wonder if the amount of chromatic aberration is determined by something like refractive index / Abbe number. If so, then a 2.41 index lens might need a very high Abbe number to be as good as CR-39.
I notice polycarbonate has less (almost no) chromatic aberration when you look through the center, but more when you look away from the center, and it’s very noticeable even with -1.25 lenses.
Perhaps it has the advantage of reminding you to look through the center, which you might forget with better lenses (higher Abbe number). If you don’t look through the center, the effective power might create cylinder effects, but I’m not really sure on the details of that.