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Thread: Is there a purpose to AR on the back side of a lens?

  1. #26
    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by smallworld View Post
    I only interjected that I've sold Antiglare on both sides of sunglasses because the coating has benefits on the front also.

    The added scratch warranty /protection is a benefit. If you are hard on your sunglasses like I am, yet want polycarbonate for eye protection during outdoors activities, the extra scratch resistant coatings are great.

    Antireflection coatings help reduce glare spots on the front and back of sunglasses, which also make the lenses look nice. Some of the coatings add a color sheen that looks like a light mirror coat. For people who want sunglasses to look expensive, the antiglare coating can add a little style. Just my opinion.

    Some anti glare coatings even make the lenses more hydrophobic, which can be nice on a sunglass if you are wearing them for activities that are in or near the water. Especially if you are doing an activity where you may want to wipe them on your shirt (even if you shouldn't).

    The backside glare spots are very distracting for me , especially driving.

    So this is why I sell antiglare on sunglasses both sides sometimes.
    There are plenty of scratch-resistant, hydrophobic coatings without anti-reflective properties that may be more appropriate for the frontside of sunglasses. I'm a huge fan of Crizal SunShield, which is essentially Crizal Avance on the back and the Avance top-coat on the front. Xperio lenses have, as I understand it, the same AR/SRC properties as SunShield.

    I'm very leery of putting an AR coating on the front side of sunglass lenses. Isn't the whole point of a sunglass lens, to oversimplify things, to increase a lens's opacity from the outside in? Doesn't putting an AR coating on the front negate some of that benefit? Isn't that why we put mirror coatings, essentially an anti-anti-reflective treatment, on the front? And, if it was optically beneficial to put an AR coating on the front side of sunglass lenses, don't you imagine sunglass specialist companies such as Maui Jim, Serengeti, Costa del Mar, Rudy Project, and Oakley, who pride themselves in marketing the optics of their lenses, would be all over it as a way to make more money?
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  2. #27
    Eyes eastward... Uilleann's Avatar
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    Barry uses front side AR on his suns regularly I believe.

    Barry, can you confirm?

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    Quote Originally Posted by AngeHamm View Post
    There are plenty of scratch-resistant, hydrophobic coatings without anti-reflective properties that may be more appropriate for the frontside of sunglasses. I'm a huge fan of Crizal SunShield, which is essentially Crizal Avance on the back and the Avance top-coat on the front. Xperio lenses have, as I understand it, the same AR/SRC properties as SunShield.

    I'm very leery of putting an AR coating on the front side of sunglass lenses. Isn't the whole point of a sunglass lens, to oversimplify things, to increase a lens's opacity from the outside in? Doesn't putting an AR coating on the front negate some of that benefit? Isn't that why we put mirror coatings, essentially an anti-anti-reflective treatment, on the front? And, if it was optically beneficial to put an AR coating on the front side of sunglass lenses, don't you imagine sunglass specialist companies such as Maui Jim, Serengeti, Costa del Mar, Rudy Project, and Oakley, who pride themselves in marketing the optics of their lenses, would be all over it as a way to make more money?
    Good points. I also went for back side only AR with sunglasses for years except for older folks who I assumed needed greater transmission, and a good AR actually lightens the dark a little bit. I only add mirrors to the front when the patient wants that "look" or when they want a darker lens, as mirrors darken the lens quite a bit. As for Maui Jim and the rest, I think their double gradient mirrors would probably not be compatible with AR, and I do think those top and bottom mirrors are useful around snow and water.

    Nowdays I generally recommend AR both sides on sunglasses but avoid the blue hues.

    I would not call a mirror the same as an AR, although they are both thin film coatings, they have the opposite effects. I think the industry should call those blue reflectors being sold as "blue protectors" what they are: MIRRORS. They are not and should not be called AR, ever. Here ends the rant.

  4. #29
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by sdgibbs View Post
    Is there a purpose to AR on the back (closer to eye) side of the lens? My understanding is this would only be useful if the lens was large enough where light from behind the lens would strike it. Light coming from in front of the lens would be seen no differently whether the lens had antiglare on the rear side correct?
    I was wearing my uncoated polarized sunglasses when I arrived for a 7:00PM July Brewers game in the mid 80's. I noticed that the light standards were starbursting with flare and haze, and as the sun went down, it became so bad that I could barely see the outfield from my usual first base lower grandstand seat. I realized that I was wearing the wrong eyeglasses, the sunglasses instead of my new Satis multilayer AR coated clear general purpose eyeglasses. From that point on, I always use multilayer AR coating (both sides) on my sunglasses, noticing a significant increase in transparency along with a decrease in fatigue when driving long distances.

    http://www.eyecarebusiness.com/artic...rticleid=50123

    There are five ghost images that can be minimized:


    1. Light entering the lens from the front that reflects off the back surface and then off the front and enters the eye.
    2. Light from the front that reflects off the cornea and then off the back surface and enters the eye.
    3. Light from the front that reflects off the cornea and then off the front surface enters the eye.
    4. Light from the back that reflects off the back surface and enters the eye.
    5. Light from the back that reflects off the front surface and enters the eye.


    #4 is the biggest concern with sunglasses- it wouldn't take much light leakage around the frame to cause reflections and starbursting. The other reflections are reduced by the tint, but are still present. Coating both sides (no problem with polarized lenses) is recommended if the sunglasses are used frequently, especially for extended periods of time, long distance driving for instance, resulting in less eye fatigue.
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  5. #30
    looking up the answers smallworld's Avatar
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    Clarifying not arguing: I didn't mean to confuse mirror coats with anti glare coatings. They are two very different coatings. I was trying to say that I believe front and backside antiglare coating makes the lenses look nicer by removing the surface glare spots. Once again, just sharing my opinion.
    What is reality but a concept unique to each of us? Can anything be classed as real when our perceptions differ greatly on so many things? Just because we see something a particular way does not make it so.

  6. #31
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by smallworld View Post
    Clarifying not arguing: I didn't mean to confuse mirror coats with anti glare coatings. They are two very different coatings. I was trying to say that I believe front and backside antiglare coating makes the lenses look nicer by removing the surface glare spots. Once again, just sharing my opinion.
    I also believe an AR coated front surface on sunglasses looks better, showing less distracting gloss and shine, with a more finished look (and also why I don't polish beveled edges). But I consider the cosmesis to be just icing on the cake so to speak, with the above listed improvements in function being the driving force for backside and/or both side AR coatings on lenses intended for protection from strong daytime light.
    Roberts Optical Ltd.
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  7. #32
    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by Dr. Bill Stacy View Post
    As for Maui Jim and the rest, I think their double gradient mirrors would probably not be compatible with AR, and I do think those top and bottom mirrors are useful around snow and water.
    Mauji Jims routinely combine the double gradient frontside mirror with backside AR. They look great and function as well as any sunglass optics I've ever seen.
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    Yeah I meant I didn't think they could put an ar on the front along with the gradient mirrors. Physically possible I suppose, but technically improbable.

  9. #34
    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by Dr. Bill Stacy View Post
    Yeah I meant I didn't think they could put an ar on the front along with the gradient mirrors. Physically possible I suppose, but technically improbable.
    I suspected that's what you meant.
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  10. #35
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    Quote Originally Posted by Dr. Bill Stacy View Post
    Yeah I meant I didn't think they could put an ar on the front along with the gradient mirrors. Physically possible I suppose, but technically improbable.
    You can definitely mix and stack various types of thin films.

    Most mirror coatings have a SiO2 over the front for protection and to keep the hydrophobic properties uniform.

    Having more than one type of substrate in a stack is actually what defines a dielectric coating.

    Putting an "AR" stack over a mirror is very similar to what enhanced aluminum mirrors are.
    Because sometimes silver isn't an option due to cost, system compatibility, or manufacturing ability.
    "AR" stacks or dielectrics are reengineered to reflect more light at certain wavelengths.
    Very possible, and very commonly done to meet spectral curve specs.


    As for AR coating on the rear of the lens. If you think of the main purpose of the AR coating is to increase light transmittance through the lens, then it is just as important as the AR coating on the front.

    Although the air-to- front lens reflections will normally be higher than the lens-to-rear surface,
    for light passing through the front of the lens.
    There is definitely a measurable transmittance increase when both surfaces are AR coated.

    Same reason why almost all professional camera lenses are AR coated on both surfaces.

  11. #36
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    Quote Originally Posted by Robert Martellaro View Post


    1. Light entering the lens from the front that reflects off the back surface and then off the front and enters the eye.
    2. Light from the front that reflects off the cornea and then off the back surface and enters the eye.
    3. Light from the front that reflects off the cornea and then off the front surface enters the eye.
    4. Light from the back that reflects off the back surface and enters the eye.
    5. Light from the back that reflects off the front surface and enters the eye.
    Based on my understanding 1,3, and 5 would be eliminated by front side AR, no?

  12. #37
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by sdgibbs View Post
    Based on my understanding 1,3, and 5 would be eliminated by front side AR, no?
    Only #3 and #5 I think, if the back is coated. #1 should continue through the back surface and not reflect off the back surface and then off the front entering the eye.
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    Quote Originally Posted by Joe Zewe View Post
    I have seen demos that demonstrate the UV reflection off the backside of a lens.

    Did it show AR caused UV reflection off the back side? Or no-AR caused UV reflection off the backside?

    Because if backside AR allowed UV to "pass through" and not reflect into the eye, wouldn't this mean frontside AR allows it to pass through directly into the eye lol which it doesnt.

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    You need to know that thin film coatings reflect the same wavelengths in the same amounts regardless of whether the radiation arrives at the film from air or from lens substrate.
    Last edited by Dr. Bill Stacy; 02-04-2016 at 11:54 AM.

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    Quote Originally Posted by Paul Smith LDO View Post
    Light comes to us from all directions and will reflect from the ocular surface back into the eye regardless of the lens size. Hence, front and back surface on clear/photochromatic ophthalmic lenses.
    Yes, even though the amount of light is small, it has tendancy to move the focus of the eye because of its seemingly near location. It can cause focus to change involuntarily, eye fatigue, and just be annoying.

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    Master OptiBoarder DanLiv's Avatar
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    Backside AR on sun seems an obvious benefit to me.

    If the question is why backside (double-side) AR clear lenses, I would think that is to tame internal lens reflections, more than to deal with light entering the backside of the lens. Light passing through from front to back of a lens reflects off both the front surface when entering and then again off the back surface when exiting. Front side AR only would not reduce the secondary reflections.

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    I think light originating from sources behind the lens is far more significant than internal reflections, because whatever wavelengths ARE reflected by the back surface are not only reflected directly at the eye and adnexa, but since it's generally concave toward the eye and the source, it's CONCENTRATED (just like a reflecting telescopic mirror) at the eye and adnexa. This is especially true of blue hue back side coatings commonly found on sunglasses and other "protective" glasses, which also reflect UV.

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    I am actually thinking of having backside AR added to my current clear pair. They apparently extend just enough past my eye to catch overhead lights behind me, and they appear as near glare on the lens, its drives me absolutely nuts.

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    Quote Originally Posted by Lelarep View Post
    I am actually thinking of having backside AR added to my current clear pair. They apparently extend just enough past my eye to catch overhead lights behind me, and they appear as near glare on the lens, its drives me absolutely nuts.
    i don't think I've ever done a backside only AR to a clear pair of lenses, only to sunlenses. Whatever wavelengths that are "passed through" from those overhead lights will reflect off the uncoated front surface back toward your eyes causing ghost images.

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    The front side has an AR/hydrophobic stack. That's exactly what I'm currently seeing, its a ghost image.

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    The only reason I see to get back side AR coated is to reduce unwanted reflections on high wrap sunglasses

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    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by ECP View Post
    The only reason I see to get back side AR coated is to reduce unwanted reflections on high wrap sunglasses
    Actually, exactly the opposite it true. High curve wrap sunglasses block out backside glare quite effectively by virtue of their shape. It's the high minus sunglass wearer (*cough cough* ME *cough cough*) who really needs the backside AR because the flatter lens pulls it away from the face, leaving lots of air space on the sides for light to reflect.
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  23. #48
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by AngeHamm View Post
    Actually, exactly the opposite it true. High curve wrap sunglasses block out backside glare quite effectively by virtue of their shape. It's the high minus sunglass wearer (*cough cough* ME *cough cough*) who really needs the backside AR because the flatter lens pulls it away from the face, leaving lots of air space on the sides for light to reflect.
    Yes. See post #29, reflection #4. Read and learn.

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  24. #49
    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    Quote Originally Posted by Lelarep View Post
    I am actually thinking of having backside AR added to my current clear pair. They apparently extend just enough past my eye to catch overhead lights behind me, and they appear as near glare on the lens, its drives me absolutely nuts.
    That’s not how the AR stack works. BS only will create a near mirror effect on the front side of clear lenses, enhancing the “ghost” effect.
    I bend light. That is what I do.

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