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An FYI for any Glasses Wearers


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#1 Master_Scythe

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Posted 16 May 2018 - 11:10 AM

Do NOT, and I mean under (almost) ANY circumstance, pay for Thinner lenses.

 

My whole life, with my "Strong prescription" (around the -4) I've always been advised to go with a High Index lens.

 

Since I found eyebuydirect (I'm not affiliated with them, but if someone is getting glasses, I'd love i you hit me up for my referral code)

I've been able to get these 'expensive thin lenses' for only about $150, to my door, not $600 locally.

I had every pair checked on the machine at the local optom, they're always exactly what I order.

 

Anyway, since they're affordable now, I never hesitated to get the thinnest I could afford....

 

Then a whole list of education kinda chanced upon me at the same time.

First, Youtube suggested  something I'd never have looked up, one of those "Heal your eyes naturally!" type videos.

It was all bullshit, but one part made me google more.

It was something along the lines of "We're starting to learn that minor aberrations and interaction between reflections at the edge of an object are a key factor.... yadda yadda yadda".

Hmm... ok.... Google google google, yep, all checks out.... Previously expected the brain was able to correct minor aberrations, but now for people who don't have perfect eyes, maybe not.... ok.... yep....

 

Then I dug further. (In ABBE charts, the higher number, the better)

 

Lens-Material-Chart---Dick-Whitney_web.p

https://www.2020mag....patients-vision

That article is from 2015, the importance of abbe has been speculated to be even greater recently.....

 

Hard Resin - is Index 1.5, normal 'plastic' lenses.  CR-39

Yes, the ones with the best visual clarity are the cheapest.

The ones people 'scare you away from' as being big and heavy...

Yes, they ARE thicker, yes they ARE heavier, but we're talking single grams, and in a -3.75 Cyl prescription, less than a 1mm thickness change (using a ruler, not a vernier)

 

To my knowledge (I emailed EBD), 1.55 is still a form of modified CR-39 which is why it's abbe value is still 'OK'.

And Trivex is just stronger. (read here if you want; https://www.allabout...es/polycarb.htm)

But I wouldn't bother with this 'sacrifice' in clarity unless you're over a 5.0 prescription. (I'm not an optom, just very experienced in glasses by this point).

 

 

People will tell you they're thinner and more delicate, and OK, so they do scratch easier.

For people with only readers which spend most of their day on their shirt, rubbing on things, maybe the scratch resistance is worth it.

However, if you wear them all day, I don't scratch my eyes with sharp objects... I'm sure you don't.... it'll be no harm.

 

I used to use GLASS sunglasses, never once broke a pair, and I was rough on them. CR39 is MUCH stronger than Glass anyway.

I've asked my 2 local optoms, I can't find a single instance reported of plastic lenses 'shattering'.

Cracks? In extreme cases yeah, but never dangerous, no shards in the eyes, just broken glasses.

 

Personally;

With my 1.7x lenses, which are polycarbonate, I honestly thought I was going colourblind.

I wouldn't get things wrong, but they'd 'flicker' before my eyes, and rotating my head slightly would clear it up.

My 1.6 Lenses were 'better' but still had this issue if I was tired.

I could focus, but I was still getting eye strain, which made 0 sense (until now).

 

I'm now wearing some 1.5 index glasses, the difference and clarity in the same prescription is phenomenal.

I paid $40 for grind lenses and frame, delivered (Over $600 locally!!) and I couldn't be happier.

 

Just thought it was information people should know.

 

1.5 lenses.

Stronger than Glass. As clear as any lens we can make (Including glass). Cheap.

 

And the Cons? ....are overplayed for marketing.

Heavier (I don't feel it), Thicker (1mm [less?] at -4ish), Delicate (I call bull, try and break a $2 pair of readers from the chemist), Scratches easier (possibly, but if you wear them during all waking hours, who cares).

 

Just my over enthusiastic FYI for the day :)


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#2 SquallStrife

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Posted 16 May 2018 - 11:59 AM

Curious.

If the CA characteristics of resin are so good, why do camera lenses use exotic mineral glasses like fluorite?

Gotta be missing something here.
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#3 Rybags

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Posted 16 May 2018 - 12:46 PM

Most plastics will scratch way easier than glass.

Most plastics suffer chemical degradation over time - think car headlights, the outer layer gets cloudy though of course it can be treated by sanding + spray laquer.

 

Most glasses are very stable and won't change over time.


Also, probably easier to achieve consistent optical characteristics with glass.



#4 Master_Scythe

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Posted 16 May 2018 - 12:56 PM

Curious.

If the CA characteristics of resin are so good, why do camera lenses use exotic mineral glasses like fluorite?

Gotta be missing something here.

 

In addition to what Rybags said, there are better ABBE values achieved by some types of glass.

But due to safety, people dont like to wear glass anymore.

Also, the cost not just for machining, but for raw blending of these special glasses (as in, the material) is significant.

 

 

For example, Crown Glass.

 

https://www.allabout...w-to-choose.htm

 

Crown glass INDEX: 1.523 ABBE: 59

 

Already better than CR39 but only by 1 point, but thats still cheap 'eye glasses' material, cameras can get more exotic materials.


Edited by Master_Scythe, 16 May 2018 - 12:58 PM.

Wherever you go in life, watch out for Scythe, the tackling IT support guy.

"I don't care what race you are, not one f*cking bit, if you want to be seen as a good people, you go in there and you f*ck up the people who (unofficially) represent you in a negative light!"


#5 SquallStrife

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Posted 16 May 2018 - 01:33 PM

OK, that all lines up with what I understood.

For some reason I was just thinking "Best" and not "Best price:performance for this particular application".
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#6 Cybes

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Posted 16 May 2018 - 02:22 PM

But due to safety, people dont like to wear glass anymore.


Not so much safety - most people aren't regularly in situations likely to break eyeglasses. It's weight. By the time your sight is bad enough that you can't do without them, those lenses a *heavy* (well, to be sitting on your nose, anyway).

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#7 merlin13

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Posted 18 May 2018 - 06:52 PM

Best argument for decent glass lens I've used in the past to slap a pushy salesman around the head 'n shoulders was to show them an old pair of glass glasses I've still got.

 

The ones with the small ball of metal embedded half-way through the toughened glass, from where an idiot work colleague managed to short out a power rail with a spanner...

 

Had no comeback at all when I also asked him in front of other customers "So your super-duper Poly-Whatever-The-Hell-You're-Insisting-To-Trying-To-Upsell-Me-To will also stop molten metal like this, will it? I specified toughened glass lens for a specific reason".

 

Shut him right up and down, in front of the actual optometrist as well.


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#8 Rybags

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Posted 18 May 2018 - 07:19 PM

Nice... but in the modern day your normal eyewear isn't supposed to substitute for proper PPE.

 

Have to ask though - did the idiot colleague join the Darwin club or is he still out there wreaking havoc?



#9 chrisg

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Posted 18 May 2018 - 09:10 PM

I've never really thought about it and I've worn glasses for years.

 

However not all plastics are going to be bad, i know I prefer a Plexiglas windscreen in front of me in my car, let alone the aircraft I fly.

 

Cheers


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#10 Rybags

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Posted 18 May 2018 - 09:34 PM

I don't think they exist actually, other than custom cars where an existing screen that suits doesn't exist.

Laminated screens are just fine IMO and I do say plexiglass hasn't been used since it'll scratch too easily.

 

As good as plastics have become they still have that weakness in that practically all of them suffer badly with age.



#11 Cybes

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Posted 18 May 2018 - 10:22 PM

...custom cars where an existing screen that suits doesn't exist.

 

Erm...Do you count racing cars as custom?  Because quite a few of those are basically standard but with everything stripped out and a cage welded in.  And the 'screen replaced with plastic.


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#12 Rybags

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Posted 18 May 2018 - 10:32 PM

I was referring more along the lines of registerable road cars.

 

Race cars, like V8SC, are actually mockups.  Just a tubular chassis, usually using factory doors and boot lid, the remainder often just being fibreglass or other composite made in the shape of the car being "raced".  So, you may as well call them custom as well. In some cases plastics are used for weight reduction - of course most formulas specify a minimum weight but it's way more desirable to have the weight down low and placed within the car to achieve the front:rear ratio that you're after.



#13 chrisg

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Posted 18 May 2018 - 10:33 PM

I don't think they exist actually, other than custom cars where an existing screen that suits doesn't exist.

Laminated screens are just fine IMO and I do say plexiglass hasn't been used since it'll scratch too easily.

 

As good as plastics have become they still have that weakness in that practically all of them suffer badly with age.

:)

 

I was probably a bit loose in my language Ry, acrylic is the commonest material used on most aircraft, especially the fast ones but even the light aircraft industry has standardised on that material in the past decade or two.

 

It really, is, to quote a corny phrase, as tough as glass and having flown double-sonics in desert conditions quite a bit I can tell you, they don't scratch - scratches on a fighter windscreen are very bad news, you want total visibility. I have seen the odd air mechanic polish out a scratch, but it is very rare. Partly that is aerodynamics of course, clean air over the screen, but it also about being able to mold a shape for the canopy. You can do that with acrylics, not really possible with glass.

 

 

I don't really know what the screen in my Pug is, probably a laminate, it's bounced the odd stone without a mark but I have had a serious rock come through a laminated screen just once and end up on the back-seat and me covered in shards - what you get driving on SA roads sometimes :)

 

I've had to replace more than one laminated screen from stone/rock damage, just as well insurance covers you for one a year usually.

 

European cars tend more to acrylic screens, especially the more expensive ones, but I doubt Japanese cars do as much.

 

The real problem with laminates, especially in hot climates, is the layers don't expand at the same rate and can crack just from thermal expansion if the surround is too stiff - seen it a number of times with friends cars, especially older Corollas.

 

Otherwise, in a car, laminates are pretty good, but in fast aircraft,whilst they are typically laminated acrylic they don't have an expansion problem. Just as well. a mate who used to fly Blackbirds tells me the screen was sometimes  too hot to touch - it gets pretty warm even in a F-4 or Mirage after a fast run :)

 

Not quite on topic at all, and I really do hear Merlin's tale, but then again I don't hang around klutzes with spanners near power lines :)

 

Cheers


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#14 Rybags

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Posted 18 May 2018 - 10:42 PM

Supposedly the reflective sunshades can cause a windscreen to crack in the right conditions... I got a coloured one, reflects less but really the aim of the game is to just keep the sunlight out, I doubt that the thing absorbing some light and passing heat makes much difference.  Imperfections like stone chips supposedly increase the chance too.

 

From some quick looking around - I don't think there are any production cars that use acrylic, polycarbonate or other plastic as the exposed windscreen component.

The problems are as I mentioned before - unstable in terms of age and too easy to scratch.

Polycarbonate has been used for a fair while in headlights - look at a car around 12 years old, they start to get fogged up.  I've used those repair kits on 3 or 4 sets and it makes them look like new but I've got real doubts the optics of a windscreen would benefit from that treatment.



#15 chrisg

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Posted 18 May 2018 - 11:17 PM

:)

 

Dunno, not a specialty of mine, but it could be as much language as anything else.

 

The aviation industry talks about "acrylic" but maybe they mean "polycarbonate. " It's not the same. Poly actually has a number of advantages, but acrylic tends to produce better visibility. In the few flight manuals I have un-boxed at the moment the mention of acrylic turns up in passing but not made a big deal of.

 

Cheers


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#16 merlin13

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Posted 19 May 2018 - 01:04 AM

Nice... but in the modern day your normal eyewear isn't supposed to substitute for proper PPE.

 

Have to ask though - did the idiot colleague join the Darwin club or is he still out there wreaking havoc?

 

We weren't welding, honest! We were supposedly doing simple maintenance on a rack of old school data comms gear. He did end up welding one end of an 8mm spanner though. My bloody spanner, which the prick never replaced either.

 

And NFI whether this clown dropped out of the gene pool or not, could only hope. Do know he got a serious arse-kicking for bringing the Customer's domestic and international data links to its knees because the rack did a complete reset due to a, ummm... "aberrant power event"...


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#17 Master_Scythe

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Posted Today, 09:19 AM

:)

 

Dunno, not a specialty of mine, but it could be as much language as anything else.

 

The aviation industry talks about "acrylic" but maybe they mean "polycarbonate. " It's not the same. Poly actually has a number of advantages, but acrylic tends to produce better visibility. In the few flight manuals I have un-boxed at the moment the mention of acrylic turns up in passing but not made a big deal of.

 

Cheers

 

Yeah, no road legal cars use it though. (with the few exotic exceptions, like ex military, or Mokes, where the windscreen... really isn't.... )

 

They're all Glass|PlasticLaminate|Glass.

 

The speed that a plastic of any kind (regardless of shatter strength) would go cloudy thanks to natural roadway sandblasting would be phenominal.

Considering Glass windscreens ALSO already suffer from this problem over years.

 

The reason your pug feels good (my mother has one about the same age as yours IIRC) is because they have a weak polarised layer in the windscreen.

It's not full polarising (as that would lower your brightness by 50%) however there is some, glare is GREATLY reduced and if I tilt my polarised sunnies, you can see the slight effect.

Trust the guy with the eyes impossibly sensitive to light here ;)


Wherever you go in life, watch out for Scythe, the tackling IT support guy.

"I don't care what race you are, not one f*cking bit, if you want to be seen as a good people, you go in there and you f*ck up the people who (unofficially) represent you in a negative light!"





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