3 ms·

Relevant previous discussion: [1] https://news.ycombinator.com/item?id=17061380 https://news.ycombinator.com/item?id=17061380 I live in Portugal and I have nee

Relevant previous discussion: [1] https://news.ycombinator.com/item?id=17061380 https://news.ycombinator.com/item?id=17061380 I live in Portugal and I have needed prescription glasses since i was a child (I'm now in my 40s). I have always felt frames particularly are priced in a cartel like way. Of course for lenses there is more of a justification depending on the thickness/prescription (it is harder to make a more curved lens that is thinner and lighter). In frames they try to get you to go for the branded style (Hugo Boss, Gucci whatever...) This is discussed extensively in the above article. [1] In lenses they try to sell you add on treatments (Anti-reflex, UV coatings, etc) In my experience some of these coatings end up shortening the lifespan of the lens as they create a surface that is easier to scratch. I think local opticians take advantage of the fact that people's face dimensions vary so much and that people need to try on tens of options before they find one that is both comfortable and good looking. Given the low prices for frames practiced by some online stores (https://www.zennioptical.com/ https://www.zennioptical.com/ for example) I'm very tempted to even buy the frames online and then going into the local opticians to get them to make and fit the lenses. I'm pretty sure they will try their best to scam me into some overcharge if I do that though...

mrob 8y ago
>they try to sell you add on treatments (Anti-reflex, UV coatings, etc) In my experience some of these coatings end up shortening the lifespan of the lens as they create a surface that is easier to scratch. In my opinion, the best material for lenses is the cheapest: plain uncoated CR-39. It has the best Abbe number of any common material (lowest chromatic aberration), and good scratch resistance. I clean mine using a microfiber cloth (carefully pre-washed to remove any grit), hot water, and dish-washing detergent. This leaves them clean enough that water will "sheet" off them, leaving them visually flawless. I find dirt on the lens more annoying than reflections, so I'd rather have uncoated lenses than coated ones that won't survive aggressive cleaning. I'd recommend CR-39 even for moderately high prescriptions. Weight of lenses increases super-linearly with size, and glasses inherently have bad off-axis performance, so there's little point wearing huge glasses where index of refraction makes a big difference. The low index of refraction of CR-39 also reduces reflections, which is important when you're omitting anti-reflective coatings. It's also worth considering that all glasses designs are trading optical performance for convenience; for maximum optical performance you need contact lenses.
- glaberficken 8y ago
  Wow, cannot upvote this comment enough. Super helpfull, thanks! Definetely going to go with uncoated lenses. Will the opticians even know what I'm talking about when I ask for CR39? I have one concern though I'm - 6 Dioptre on each eye. so lens weight has always been an issue for me. even a few grams extra make a big difference. I always go for rectangular low profile lenses with the greatest thickness reduction they can apply and they always advise for Polycarbonate lenses. What's your take on this?
  - mrob 8y ago
    All glasses are a compromise in some way, so you have to decide which flaws are most tolerable to you. -6 is strong enough correction that I'd seriously consider contact lenses if I needed it. Contact lenses avoid the image distortion and shrinkage you get with glasses, and because they move with your eyes, the image is sharp in all parts of your field of vision. Polycarbonate is IMO a terrible material for corrective lenses. It has very bad Abbe number, so you get a lot of chromatic aberration (rainbow artifacts) and it's very soft, so coating is pretty much required. Its only real virtue is impact resistance, which is important in safety glasses, but you can get flat safety glasses that fit over your corrective glasses. The weight is marginally better than CR-39, but not enough to make up for the poor optical performance. I haven't seen it person, but going by the numbers, Trivex seems superior. Wikipedia has some information on common materials: https://en.wikipedia.org/wiki/Corrective_lens#Lens_materials https://en.wikipedia.org/wiki/Corrective_lens#Lens_materials My preference for uncoated applies only to CR-39. Other materials have properties that make coatings more important. It's also possible that some coatings have much better resistance to cleaning than others. Unfortunately, details about coatings are generally secret, so there's no way to evaluate them.
    - glaberficken 8y ago
      I see, thanks for the advice again I will read more about it. Yeah i wear daily contacts for beach / swimming days, but unfortunately never managed to get used to wearing contacts as primary everyday correction.

mrob 8y ago

>they try to sell you add on treatments (Anti-reflex, UV coatings, etc) In my experience some of these coatings end up shortening the lifespan of the lens as they create a surface that is easier to scratch. In my opinion, the best material for lenses is the cheapest: plain uncoated CR-39. It has the best Abbe number of any common material (lowest chromatic aberration), and good scratch resistance. I clean mine using a microfiber cloth (carefully pre-washed to remove any grit), hot water, and dish-washing detergent. This leaves them clean enough that water will "sheet" off them, leaving them visually flawless. I find dirt on the lens more annoying than reflections, so I'd rather have uncoated lenses than coated ones that won't survive aggressive cleaning. I'd recommend CR-39 even for moderately high prescriptions. Weight of lenses increases super-linearly with size, and glasses inherently have bad off-axis performance, so there's little point wearing huge glasses where index of refraction makes a big difference. The low index of refraction of CR-39 also reduces reflections, which is important when you're omitting anti-reflective coatings. It's also worth considering that all glasses designs are trading optical performance for convenience; for maximum optical performance you need contact lenses.

glaberficken 8y ago
Wow, cannot upvote this comment enough. Super helpfull, thanks! Definetely going to go with uncoated lenses. Will the opticians even know what I'm talking about when I ask for CR39? I have one concern though I'm - 6 Dioptre on each eye. so lens weight has always been an issue for me. even a few grams extra make a big difference. I always go for rectangular low profile lenses with the greatest thickness reduction they can apply and they always advise for Polycarbonate lenses. What's your take on this?
- mrob 8y ago
  All glasses are a compromise in some way, so you have to decide which flaws are most tolerable to you. -6 is strong enough correction that I'd seriously consider contact lenses if I needed it. Contact lenses avoid the image distortion and shrinkage you get with glasses, and because they move with your eyes, the image is sharp in all parts of your field of vision. Polycarbonate is IMO a terrible material for corrective lenses. It has very bad Abbe number, so you get a lot of chromatic aberration (rainbow artifacts) and it's very soft, so coating is pretty much required. Its only real virtue is impact resistance, which is important in safety glasses, but you can get flat safety glasses that fit over your corrective glasses. The weight is marginally better than CR-39, but not enough to make up for the poor optical performance. I haven't seen it person, but going by the numbers, Trivex seems superior. Wikipedia has some information on common materials: https://en.wikipedia.org/wiki/Corrective_lens#Lens_materials https://en.wikipedia.org/wiki/Corrective_lens#Lens_materials My preference for uncoated applies only to CR-39. Other materials have properties that make coatings more important. It's also possible that some coatings have much better resistance to cleaning than others. Unfortunately, details about coatings are generally secret, so there's no way to evaluate them.
  - glaberficken 8y ago
    I see, thanks for the advice again I will read more about it. Yeah i wear daily contacts for beach / swimming days, but unfortunately never managed to get used to wearing contacts as primary everyday correction.