Anti Reflection Reducing Impact Resistance

[jackraider]

I recently read that adding an Anti reflection coating to a lens reduces its impact resistance. After asking some lab guys who are more knowledge about these things than I, I learned that that anything done to a lens after it is made reduces its impact resistance. So I have a few more questions that were left unanswered and more that have come up?

So here is the question:
· What is the impact resistance of a each lens material?
· What does impact resistance mean? (I what to make sure I understand this term correctly)
· How much is each lens material’s impact resistance reduced when it undergoes: Surfacing, Edging, AR coating, Scratch coating, Hand Edging, Polishing, AR coating, Scratch Coating, Mirror Coating, Polarizing, Tinting and any other process?

If you know the answers this will be really helpful.

[MakeOptics]

I recently read that adding an Anti reflection coating to a lens reduces its impact resistance. After asking some lab guys who are more knowledge about these things than I, I learned that that anything done to a lens after it is made reduces its impact resistance. So I have a few more questions that were left unanswered and more that have come up?

So here is the question:
· What is the impact resistance of a each lens material?
· What does impact resistance mean? (I what to make sure I understand this term correctly)
· How much is each lens material’s impact resistance reduced when it undergoes: Surfacing, Edging, AR coating, Scratch coating, Hand Edging, Polishing, AR coating, Scratch Coating, Mirror Coating, Polarizing, Tinting and any other process?

If you know the answers this will be really helpful.

The materials that make up an ARC stack are brittle and when they crack on impact, these cracks have the ability and tendency to propagate through the material. So with mirrors and ARC's yes they reduce the impact resistance slightly. Not any treatment, if you were to coat with a more impact resistant coating you would actually increase the lenses impact resistance, again slightly.

Impact resistance - The impact resistance of lenses subject to individual tests shall be measured with a 15.9-mm(5/8-in)-diameter steel ball, weighing not less than 16 grams (0.56 oz) dropped from a height of
not less than 127 cm (50 in). Source: ANSI 2010

Last ? is a good one, I don't have an answer for that and it would be hard to get one as multiple variables will exist in each of your scenarios, for instance surfacing what's the water temperature or slurry temperature, grit of the pads or polishing tools, etc. Figure thickness into the equation and you would be hard pressed to find any metric other than it's ability to meet certain impact requirements.

You might want to check out wolfram.com to plug in some material searches.

[Chris Ryser]

Effect of multiple antireflection coatings on impact resistance of Hoya Phoenix spectacle lenses.

Chou BR1, Hovis JK.
Author information


Abstract

PURPOSE:

To investigate how the impact resistance of Hoya Phoenix spectacle lenses is affected by centre thickness and the application of a multilayer antireflection (MAR) coating.
METHODS:

Four groups of plano lenses were tested: dress thickness with scratch resistant (SR) coating on both surfaces, dress thickness with SR and MAR, industrial thickness with SR and industrial thickness with SR and MAR. Lenses were edged to a clear circular aperture of 50 mm with a 0.5 mm hidden bevel and mounted in a specially-designed lens support. A pneumatic gun was used to propel a 6.35 mm steel ball at the centre of each lens. Impact speed was varied using the ZEST protocol to determine the threshold breakage speed.
RESULTS:

The threshold breakage speeds of the dress and industrial thickness SR lenses were 55.1 and 63.2 m/s, respectively and the corresponding threshold breakage speeds for SR-MAR lenses were 50.1 and 54.7 m/s. All comparisons were statistically significant using Student's t-test with a rejection level of p < 0.005. Unlike polycarbonate lenses, dress thickness Phoenix lenses do not display 'oilcanning' deformation on high energy impact and therefore are less likely to be dislodged from their mountings.
CONCLUSIONS:

We found that the mean impact resistance of the Phoenix lenses was greater than the level required of eye protector lenses by the standards AS/NZS 1337:1992, ANSI Z87.1-2003 and CSA Z94.3-02. Similar to CR39 and polycarbonate, the application of MAR to Phoenix lenses reduces their impact resistance, however, they provide an acceptable level of impact protection in industrial settings, where there is little danger of exposure to pointed or sharp-edged high-speed missiles.

Source: -----------> http://www.ncbi.nlm.nih.gov/pubmed/16494611

[drk]

Nice post, Makey.

[MikeAurelius]

As long as you maintain a reasonable CT/ET combination, the overall impact resistance should not affected all that much. Less than 1% failure? Personally, I like those odds, they are very close to an untreated lens.

Now, when it comes to Z87, there are a bunch of reasons NOT to further treat a lens with A/R or a scratch coating. I've never heard of a Z87 requirement for Mirror or polarizing, although someone who works outside could require more than a dark tint.

And remember, the drop ball test is supposed to be done AFTER all treatments are done (although they are waived if the lenses are laminated). I'm at home, so I don't have my copy of the latest standard on that, any care to comment?