# Optical Forums > Ophthalmic Optics >  Backside AR Coating on Sun Lenses

## dochsml

I'm looking to purchase a pair of quality polarized prescription lenses. I get differing opinions on whether to AR coat the backside only, or to coat both sides, or just leave them uncoated. What does everyone think? And more importantly, what kind of facts backup the opinions?

----------


## Ace

Coat both sides. Coating the backside does little, as the light still reflects off the front surface back to your eye. The frontside will be harder to clean in comparison to the backside, especially if it has super hydrophobic.

----------


## dochsml

> Coat both sides. Coating the backside does little, as the light still reflects off the front surface back to your eye. The frontside will be harder to clean in comparison to the backside, especially if it has super hydrophobic.


 
Why do labs seem to want to charge more for backside only? Can they put only hydro on the front side?

----------


## Ace

> Why do labs seem to want to charge more for backside only? Can they put only hydro on the front side?


 Because it has to be separated, and masked. And the coating lab runs the risk of ruining the lenses simply by coating both sides accidentally if it is missed or improperly marked on the coating order envelope.

----------


## dochsml

> Because it has to be separated, and masked. And the coating lab runs the risk of ruining the lenses simply by coating both sides accidentally if it is missed or improperly marked on the coating order envelope.


Then why is backside only so popular if it costs more and performs less?

----------


## Ace

> Then why is backside only so popular if it costs more and performs less?


 Because.... some people are uneducated.It has become quite the myth

----------


## Ace

> Because it has to be separated, and masked. And the coating lab runs the risk of ruining the lenses simply by coating both sides accidentally if it is missed or improperly marked on the coating order envelope.


 In response to frontside only hydrophobic, yes but not many labs no how to do it correctly

----------


## dochsml

makes sense. what's it take to do it correctly? a little sio2, a little hydro and presto!


:cheers:

----------


## Ace

> makes sense. what's it take to do it correctly? a little sio2, a little hydro and presto!
> 
> 
> :cheers:


 and a little chromium and plasma treatment

----------


## dochsml

> and a little chromium and plasma treatment


thanks ace.

anybody else care to comment?

----------


## AEOC

Wouldn't coating both surfaces increase light transmission of the lens?

----------


## apaul

Kodak stock pre-tinted lens with AR on back surface (in the UK)
great lenses

----------


## dochsml

> Wouldn't coating both surfaces increase light transmission of the lens?


Yes it would. But I guess it wouldn't be significant if the lens was tinted already. I think it has become clear that the pluses far outweigh the minuses on this one.

----------


## For-Life

the labs I deal with sell the backside AR for much less expensive than both side AR.

When it comes down to it, the backside AR does give a major benefit to the lenses.  I have had sunglasses without a backside AR and the visual quality is diminished.  Coating both sides may be nice, but putting the coating on the front of a tinted sun lens offers no additional visual advantage, as a sun lens already cuts down on light transmission.

----------


## dochsml

> the labs I deal with sell the backside AR for much less expensive than both side AR.
> 
> When it comes down to it, the backside AR does give a major benefit to the lenses. I have had sunglasses without a backside AR and the visual quality is diminished. Coating both sides may be nice, but putting the coating on the front of a tinted sun lens offers no additional visual advantage, as a sun lens already cuts down on light transmission.


I agree. But I would still like to see hydrophobic applied to the front without AR. Most labs don't offer that. Or at least offer it the way Ace was describing in the vacuum chamber. Kind of annoying having a slick backside and rough front! Of course then we are back to having to separate out work and the lab charging a premium.

----------


## For-Life

> I agree. But I would still like to see hydrophobic applied to the front without AR. Most labs don't offer that. Or at least offer it the way Ace was describing in the vacuum chamber. Kind of annoying having a slick backside and rough front! Of course then we are back to having to separate out work and the lab charging a premium.


true, but consumers never complained about how hard it was to clean a non-coated lens, only a coated lens.

----------


## dochsml

> true, but consumers never complained about how hard it was to clean a non-coated lens, only a coated lens.


It is getting better though. Anti static and oleophobic coatings seem to help. AR will always be harder to clean because of what clean is on AR lenses. Increase the transmission and see more dirt!

----------


## AWTECH

ACE: 


> Coat both sides. Coating the backside does little, as the light still reflects off the front surface back to your eye. The frontside will be harder to clean in comparison to the backside, especially if it has super hydrophobic.


I have to disagree with AR on the front of a sunlens.  AR will increase light transmission.  The purpose of AR on the backside of a Polarized lens is to prevent reflections that would occur on the rear lens surface.  With a silicon based hard coating todays hydrophobics will bond to the front surface.

AR on the front will only increase light transmission and that is not what you want with a sunlens.

----------


## dochsml

> ACE: 
> 
> I have to disagree with AR on the front of a sunlens. AR will increase light transmission. The purpose of AR on the backside of a Polarized lens is to prevent reflections that would occur on the rear lens surface. With a silicon based hard coating todays hydrophobics will bond to the front surface.
> 
> AR on the front will only increase light transmission and that is not what you want with a sunlens.


I was under the impression that most hydrophobics and oleophobics are engineered to stick best to the last layer of AR (almost always SiO2)? I'm sure it would work on the hard coat, but maybe not as well. Maybe flash mirror is the way to go?

----------


## AWTECH

dochsml: 


> I was under the impression that most hydrophobics and oleophobics are engineered to stick best to the last layer of AR (almost always SiO2)? I'm sure it would work on the hard coat, but maybe not as well. Maybe flash mirror is the way to go?


You seem to be asking very specific questions yet using general assumptions of materials.  Very few who apply hydrophobics formulate their own coating.  Generally you are correct that the bonding is to the Silicon in the SiO2.  A polysiloxane hard coating is silicon based and depending on the hydrophobic will likely bond in a similar manner.  Also a mirror will allow good bonding.

There are many factors involved in applying proper mirrors, ARs and hydropobics.

We have tested and developed our own process to work with our ICE-TECH Advanced Polarized Lenses.  We have excellent results on non-mirror and mirror lenses with our Free-ICE Super Hydrophobic

----------


## dochsml

> dochsml: 
> 
> You seem to be asking very specific questions yet using general assumptions of materials. Very few who apply hydrophobics formulate their own coating. Generally you are correct that the bonding is to the Silicon in the SiO2. A polysiloxane hard coating is silicon based and depending on the hydrophobic will likely bond in a similar manner. Also a mirror will allow good bonding.
> 
> There are many factors involved in applying proper mirrors, ARs and hydropobics.
> 
> We have tested and developed our own process to work with our ICE-TECH Advanced Polarized Lenses. We have excellent results on non-mirror and mirror lenses with our Free-ICE Super Hydrophobic


How is this hydrophobic applied? In or out of chamber?

----------


## AWTECH

Our ICE-TECH Free-ICE is applied in a chamber.  Unfortunately any additional information about our unique process is proprietary.

We invested a great deal in development and testing and provide limited information on the details of our processes.

----------


## dochsml

> Our ICE-TECH Free-ICE is applied in a chamber. Unfortunately any additional information about our unique process is proprietary.
> 
> We invested a great deal in development and testing and provide limited information on the details of our processes.


Most everyone uses the same super hydrophobic / oleophobic chemical but the difference is in application. I would certainly never ask you to show your cards on your specific method. Was more curious if it was done under vacuum or not? I know they have some atmospheric chambers for applying as well along with dips and wipes and who knows what else. A PVD chamber could do it all whereas a sputtered mirror would require some other means of applying the hydro. I'm just enjoying the conversation now. My next pair is definitely going to be polarized. I think I might be able to talk someone into making sure there is hydro on both sides.

:cheers:

----------


## Ory

> ACE: 
> 
> I have to disagree with AR on the front of a sunlens. AR will increase light transmission. The purpose of AR on the backside of a Polarized lens is to prevent reflections that would occur on the rear lens surface. With a silicon based hard coating todays hydrophobics will bond to the front surface.
> 
> AR on the front will only increase light transmission and that is not what you want with a sunlens.


Yes!  Going without the frontside AR is also the cheap man's mirror coat.  Look at the vast majority of sun lenses without an AR coat in full sunlight.   The reflections are great!

----------


## sharon m./ aboc

> ACE:  
> 
> I have to disagree with AR on the front of a sunlens. AR will increase light transmission. The purpose of AR on the backside of a Polarized lens is to prevent reflections that would occur on the rear lens surface. With a silicon based hard coating todays hydrophobics will bond to the front surface.
> 
> AR on the front will only increase light transmission and that is not what you want with a sunlens.


Well put....
This is EXACTLY what my understanding of the purpose of "backside only" a/r on sunglasses....You don't want more light transmission on sunglasses.

----------


## dochsml

> Well put....
> This is EXACTLY what my understanding of the purpose of "backside only" a/r on sunglasses....You don't want more light transmission on sunglasses.


Anyone know how much the AR will actually increase the light transmission on sunglasses? It's obviously not going to negate a tint or mirror. It may actually reduce back reflection from the front side.

----------


## AWTECH

Depending on lens material light transmission may increase by 2% to 4%.

----------


## dochsml

> Depending on lens material light transmission may increase by 2% to 4%.


2% to 4% less light would also be back reflected from the front?

----------


## chip anderson

Backside AR is not to increase light transmission but to stop reflected glare from a source behind the wearer from reflecting into the eye and obviateing the images in front of the wearer.


Chip

----------


## dochsml

> Backside AR is not to increase light transmission but to stop reflected glare from a source behind the wearer from reflecting into the eye and obviateing the images in front of the wearer.
> 
> 
> Chip


We were discussing the plus and minus of front side AR on sunglasses though. Increase transmission thus defeating the fact that it is a sunglass somewhat or does it actually reduce any back reflected light from the front side surface due to this increase in transmission.

----------


## AWTECH

There is no advantage to front side AR on a sunlens that you intend use to block light.  I thought I was clear on this point. dochsml, you seem to try to make a reason to use this front AR.  If you want front AR and can order it I suggest you do.

----------


## dochsml

> There is no advantage to front side AR on a sunlens that you intend use to block light. I thought I was clear on this point. dochsml, you seem to try to make a reason to use this front AR. If you want front AR and can order it I suggest you do.


Not trying to make a case. Just want to discuss all the ins and outs. You seem to be the only one making a case against it. It seems that this is the standard in the industry yet is debated in my circle. As you can see from my # of posts, I am new to this board and would like to hear the opinions (preferrably fact based) of people in the business whom I would otherwise never hear from. I've actually decided to go with a front side flash mirror and backside AR but would still like to hear from people on the subject. Sorry if I irritated you with my beating of a dead horse on this, that wasn't my intention. I really appreciate all the facts you have contributed to this thread. I wouldn't go as far as to say that there are NO reasons not to use front side AR though. Following the thread, there is the possibility of a surcharge for backside only, no hydro on the front, and the possibilty of reducing reflection. In fact, ACE seems to take the exact opposite viewpoint of you. That being said, your point of purposely increasing the transmission of a lens that is supposed to do the opposite is well taken. If you can't tell, this is more than just a casual interest of mine. My background is with PVD thin films only some of which include visual AR but I don't pretend to know it all. Like I said before, I've already made my decision but am still hungry for information and everyones' input in a real life application.

----------


## AWTECH

dochsml:  Since you know thin film principals I can explain it this way.  Why for almost no benefit attempt AR on the front?  The other fact to consider is that due to the fact that cost of production is a factor most producers of AR and mirrors keep known repeatable processes as there standard.

I constantly get requests for a mirror color that is not currently offered.  When we tell them the development costs of a new mirror including testing, all have changed their mind.  Many custom options are possible it is just how much do you want to pay.

I see know potential benefit.  We have actually tested SiO2 on the front surface for hydrophobic bonding to see if there was any additional bonding compared to the Silicon in the hard coating.  So your thought process has been explored by me personally.  Hard coating, AR thickness etc. are all important componates of a complete quality lens.

----------


## Jedi

As well as front-side AR having very little use on a sunglass lens, I find in certain light the residual colour from the AR becomes more obvious and alters the over-all look of the sunglass. It can alter it to the point of the client thinking their is a coloured mirror on the front surface.

----------


## For-Life

Also, clients tend to hate the front side AR, because it makes their eyes more visable through the tint

----------


## chip anderson

Not to mention that front-side AR scratches a lot easier that a lens without same.  People tend to get thier sunglasses in situations that are more likely to create scratches.


Chip

----------


## Chris Bowers

It is my understanding that at best we are talking about less than 2% and Ill let others who know more about this process explain. Most important I would think is that AR coating allows light to enter the eye at a usable angle. Glare from the front surface of a lens doesnt just bounce away without an undesired affect. For that last 2% we can let the iris do it's job.

----------


## dochsml

> AWTECH:
> dochsml: Since you know thin film principals I can explain it this way. Why for almost no benefit attempt AR on the front? The other fact to consider is that due to the fact that cost of production is a factor most producers of AR and mirrors keep known repeatable processes as there standard.
> 
> I constantly get requests for a mirror color that is not currently offered. When we tell them the development costs of a new mirror including testing, all have changed their mind. Many custom options are possible it is just how much do you want to pay.
> 
> I see know potential benefit. We have actually tested SiO2 on the front surface for hydrophobic bonding to see if there was any additional bonding compared to the Silicon in the hard coating. So your thought process has been explored by me personally. Hard coating, AR thickness etc. are all important componates of a complete quality lens.


That's a very valid point. More consumables to apply the front side AR, more cost to the lab. And I know what you mean about the mirrors. Not to mention the people that want double gradients which require special tooling. I just got a bad taste in my mouth by a lab wanting to charge me more for backside only because they mostly do both side AR and would have to "separate" it out. This raised my eyebrow since I figured they would just stop processing it after the back side hence less consumables. And I certainly didn't want to pay any more to not get front side hydro. I thought about getting both side AR to get something that I wanted (front side hydro) and pay less than backside only. That is why I decided on the flash mirror.(costs the same as both side AR *shrug*). I would be curious to see your test results on the hyrdro to hard coat (i assume that is also with no ion gun treatment), but I'm not going to ask. Thanks for your input.





> chip anderson:
> 
> Not to mention that front-side AR scratches a lot easier that a lens without same. People tend to get thier sunglasses in situations that are more likely to create scratches.
> 
> 
> Chip


I would have to disagree. AR should not scratch as easily. In fact, it should raise the bayer ratio by some amount. The problem is the fact that the transmission is being increased, it makes scratches much more apparent.

----------


## hipoptical

If you would just do it the right way from the beginning, this thread would not exist:
Polarized lenses, mirror coated, backside A/R, super-hydrophobic both sides. 
No worries, no hassels, no reflections. Just pure, clear vision. I have 3 pair.

----------


## dochsml

> If you would just do it the right way from the beginning, this thread would not exist:
> Polarized lenses, mirror coated, backside A/R, super-hydrophobic both sides. 
> No worries, no hassels, no reflections. Just pure, clear vision. I have 3 pair.


You hit the nail right on the head. There are a lot of labs that DON'T do it correctly.

----------


## APVaccountrep

> Kodak stock pre-tinted lens with AR on back surface (in the UK)
> great lenses


I agree...Outstanding for those who finish only

----------


## Ace

> dochsml:  Since you know thin film principals I can explain it this way.  Why for almost no benefit attempt AR on the front?  The other fact to consider is that due to the fact that cost of production is a factor most producers of AR and mirrors keep known repeatable processes as there standard.
> 
> I constantly get requests for a mirror color that is not currently offered.  When we tell them the development costs of a new mirror including testing, all have changed their mind.  Many custom options are possible it is just how much do you want to pay.
> 
> I see know potential benefit.  We have actually tested SiO2 on the front surface for hydrophobic bonding to see if there was any additional bonding compared to the Silicon in the hard coating.  So your thought process has been explored by me personally.  Hard coating, AR thickness etc. are all important componates of a complete quality lens.


There is hardly any benefit in just coating the back either! The light reflects off the front surface. The 2 percent you gained just got cut in half or worse. You can still see your own freakin eye on a 8 base poly lens! If the front side is AR coated it allows most of the back light to pass through. Take uncoated polarized samples, backside AR only, and both side coated and measure transmission values through the front, then through the back and you'll see what i'm talking about. Yes, I have done this personally. I also have done testing with putting Hydrophobics and Oleophobics on lenses without SIO2 and have found that the longterm adhesion was better with the SIO2 film present. This has to do with the design of the polymers used in the tests (we only used polymers that were in large scale use representing 70% of the Market), so their may be polymer designs out there that work fine with lacquer only.

----------


## Ace

> Not to mention that front-side AR scratches a lot easier that a lens without same.  People tend to get thier sunglasses in situations that are more likely to create scratches.
> 
> 
> Chip


Then you are using a bad coating! The coating increases scratch resistance. What if someone wants a mirror front, that'll really show scratches too! By that logic we shouldn't coat anything!!!!

----------


## Ace

> There is no advantage to front side AR on a sunlens that you intend use to block light.  I thought I was clear on this point. dochsml, you seem to try to make a reason to use this front AR.  If you want front AR and can order it I suggest you do.


Wow! Are you serious. I guess when you say something we should fetch Moses and run up to the mountain and put it on the stone tablets!

----------


## Ace

> Backside AR is not to increase light transmission but to stop reflected glare from a source behind the wearer from reflecting into the eye and obviateing the images in front of the wearer.
> 
> 
> Chip


So you are saying that Backside AR doesn't increase transmission, but diminishes reflection? How's that work exactly?

----------


## Ace

> Also, clients tend to hate the front side AR, because it makes their eyes more visable through the tint


This is not from the AR, but from the tint not being bleached back before its sent to the coating facility. The ultrasonic cleaning will bleach it back 10 - 20% if you don't do this. Then the degassing oven will also diminish the tint as well.

----------


## Ace

> dochsml: 
> 
> You seem to be asking very specific questions yet using general assumptions of materials. Very few who apply hydrophobics formulate their own coating. Generally you are correct that the bonding is to the Silicon in the SiO2. A polysiloxane hard coating is silicon based and depending on the hydrophobic will likely bond in a similar manner. Also a mirror will allow good bonding.
> 
> There are many factors involved in applying proper mirrors, ARs and hydropobics.
> 
> We have tested and developed our own process to work with our ICE-TECH Advanced Polarized Lenses. We have excellent results on non-mirror and mirror lenses with our Free-ICE Super Hydrophobic


 
Did anyone ask about your specific products? You seem to make a lot of assumptions yourself, on lacquers and mirrors, of which there are many types.

----------


## Ory

> So you are saying that Backside AR doesn't increase transmission, but diminishes reflection? How's that work exactly?


Actually he said (or implied) that the purpose of a backside AR is not to increase transmission but instead reduce reflections.  The really annoying reflections from behind will be reduced and you will also have fewer reflections from the back surface - front surface - eye route.

----------


## For-Life

> This is not from the AR, but from the tint not being bleached back before its sent to the coating facility. The ultrasonic cleaning will bleach it back 10 - 20% if you don't do this. Then the degassing oven will also diminish the tint as well.


 
There are reflections on the front of the sun lens.  If you remove those reflections the lens appears more transparent.

----------


## hipoptical

If you people would do what I do, this discussion wouldn't be taking place. Do it right the first time: as a professional, fit your patient/customer in a wrap frame, polarized lenses with a REAL hard coat, mirror the front (flash, solid, gradient, whatever) and be done with it. A good wrap will prevent backside reflections since light cannot reach the surface of the lens. If you don't wrap, then use backside A/R to reduce reflections. It is a sun lens- why are some of you even talking about increasing light transmission? If you want more light in the eye, use a gray or brown 'B' instead of 'C'.
The bottom line to the original query is this: backside A/R is beneficial, but not necessary. Professionals understand this, and do what they can to ensure that it is used when appropriate. (Use of it with a wrap is generally overkill.) One will find that whether the lens is polarized or not has some bearing on how important it is to use or not use backside A/R. Easiest way to resolve this issue for yourself is to try several different configurations. What you will find in the end, though, is that my suggestions are spot-on.
And by-the-way: if you are still tinting lenses to make sunglasses... shame on you!

----------


## For-Life

> If you people would do what I do, this discussion wouldn't be taking place. Do it right the first time: as a professional, fit your patient/customer in a wrap frame, polarized lenses with a REAL hard coat, mirror the front (flash, solid, gradient, whatever) and be done with it. A good wrap will prevent backside reflections since light cannot reach the surface of the lens. If you don't wrap, then use backside A/R to reduce reflections. It is a sun lens- why are some of you even talking about increasing light transmission? If you want more light in the eye, use a gray or brown 'B' instead of 'C'.
> The bottom line to the original query is this: backside A/R is beneficial, but not necessary. Professionals understand this, and do what they can to ensure that it is used when appropriate. (Use of it with a wrap is generally overkill.) One will find that whether the lens is polarized or not has some bearing on how important it is to use or not use backside A/R. Easiest way to resolve this issue for yourself is to try several different configurations. What you will find in the end, though, is that my suggestions are spot-on.
> And by-the-way: if you are still tinting lenses to make sunglasses... shame on you!


 
I argue that it is more important to have a backside AR than a polarized lens.  Without a backside AR I find way too much glare, as in ghost images.  With a polarized lens I do not find that the vision is much better.

----------


## hipoptical

> I argue that it is more important to have a backside AR than a polarized lens.  Without a backside AR I find way too much glare, as in ghost images.  With a polarized lens I do not find that the vision is much better.


You could be correct, depending on your evvironment. I would think that the effects of the sun are either washed-out or enhanced, depending on your situation. If I still lived over-seas, high on the globe, I would say that the need for a polarized lens wasn't as important, since grass doesn't cause much glare. I am now back in Texas. The sun is bright, and the glare from cars, buildings, streets, water, etc. is truly blinding. I have a really cool pair of non-polarized 'shades that sit on my dresser. Can't wear them. Backside A/R does nothing for driving *into* the rising or setting sun. It also does nothing driving away from the sun if you are looking into the rear of a fully decked-out F350 Dually with the sun shining right at it. Backside A/R also doesn't help if your are wearing wrapped sunglasses, since light doesn't reflect on what it cannot reach (as I already said). Apart from any situations like these, you are right. 
I would still argue that the best alternative is to wear polarized, mirrored, a/r coated lenses. Why settle for "next-best" or "similar to"?

----------


## jrctx

I want to underscore the use of backside AR for those that do not get wrap lenses.  Most of the opticians I have seen do not consider wrap lenses in an Rx form.  I guess it is due to the lack of knowledge at the retail and wholesale lab level.

----------


## chip anderson

Hippoptical:  

Obviously you have never had the sun behind you (as in fishing) in the South.  Glare from the backside can make *everything* disappear and you trying to see that monster bass you don't want this to happen.

Chip

The reason you do this is you want light transmission from the back *through* the front, not back toward the eye.

----------


## hipoptical

Chip....
I failed to be as clear as I intended. I meant that backside A/R does nothing for the reflected glare off the back of the truck in front of you when the sun is behind. I also stated more than once that I think the combination is the key; polarized, mirror, a/r. Now, I can honestly say that I have never lost a bass because of the sun reflecting off the back of my lenses. This is for two reasons: 1. I wear wrap sunglasses that allow no light in from the back (I'm a -500 -125 ou) and 2. I don't go after that one big bass; we are not particular about our fishing (dad and I). As long as it fits in the frying pan it's a good one. We normally catch 20-40 when we go out, all legal keepers. We go after sandies (white bass for you non-Texans), hybrids, stripers, and catfish normally, and every once-in-a-while we'll go for crappies. We leave the "big bass" to those who fish for sport and have too much patience.
My bottom line: backside a/r is recommended IF you don't wear a wrap. If you do wear a wrap, it's just extra goodness. Hope that's a little clearer.

----------


## jherman

Seeing the target is more important than glare reduction to sight fisher. 

If anyone has a better mousetrap to increase spotting VA, first rounds on me. Reducing or eliminating blue light is the most common choice for spotting your target.

Bait fishers can choose whatever they think is the prettiest, mirrors included.

The more backlight a pair of fishing specs have, the more necessary a backside AR is.
tight lines
James

----------

