Thursday, June 12, 2008

Shooting Glasses, Part 2

In response to my earlier article about shooting glasses, I received a question in the COMMENTS asking about specific brand names and whether "they are all polycarbonate lenses".

A few minutes of online research provided more useless information than you want to read here. Essentially, the named brands are "fashion sunglasses", and the emphasis is on shape and finish (or tint). There are categories for "sport glasses", but even there I was unable to find information on "impact resistance" or even, most commonly, UV protection or thickness/light-weight/flexibility of the material of which the lenses are made.

If we're looking for answers, here are a few:
  • Polycarbonate plastics are generally regarded as the standard for impact resistance
  • Polycarbonate lenses provide UV A and UV B protection.
  • UV C protection is that provided in Welders Goggles, and are not typically provided by Polycarbonate materials in lightweight glasses.
  • If the purpose of wearing Range Glasses is to protect your eyes from damage or industry due to the high-velocity impact of small particles of foreign matter, lenses should be made of Polycarbonate plastics at a minimum.
  • When buying Range Glasses, it is not safe to assume that the lenses are made of Polycarbonate material unless the manufacturer specifically says they are.
What other materials are available?

During my research, I ran across this article which defines and describes Polycarbonate plastic as Impact Resistant lense material.

The article also identifies and describes (briefly) another, newer (and more expensive) material called "Trivex".

An article on Trivex vs Polycarbonate describes the differences:

Born from the space race in the 1960's and introduced to the ophthalmic lens market in the late 1970's, polycarbonate has been around the block a few times and enjoys a sizeable [sic] market share, particularly in children's and safety eyewear due to its superior impact resistance. With a higher index of refraction and lower specific gravity, polycarbonate lenses are thinner and lighter than their plastic and glass counterparts. Inherent UV protection and wide product availability also contribute to its popularity.

Polycarbonate, however, is not without its drawbacks. One of the chief complaints about polycarbonate is its optical quality, or lack thereof. With an Abbe value of 29, polycarbonate's chromatic aberration is the highest of any lens material in use today. Furthermore, with the increase in popularity of drill mount frames, some dispensers are hesitant to use polycarbonate because of its lack of tensile strength and likelihood of cracking around drill holes.

Enter Trivex

Introduced in 2001 by PPG [Pittsburgh Plate Glass], as the only lens material other than polycarbonate to pass FDA Impact Resistance Test ... the High Velocity Impact Test, and meet ANSI Z87.1 '89 standards, Trivex has been slowly increasing in both popularity and availability. While Trivex has a slightly lower refractive index (1.53 compared to 1.58), it's specific gravity, 1.11g/cm3, makes it the lightest of any lens material available today. Like polycarbonate, Trivex also has inherent UV protection. However, unlike polycarbonate, Trivex has an Abbe value of 45, making it optically superior. Further distinguishig [sic: 'distinguishing'?] itself, Trivex is ideal for drill mounting. The tensile strength of Trivex makes it highly resistant to cracking around drill holes, so much in fact, Younger Optics guarantees its Trivex products (Trilogy) for life, against stress fractures and drill mount cracking.


In summary, Trivex has the impact resistance and inherent UV protection of polycarbonate. With a lower index of refraction, Trivex may be slightly thicker than polycarbonate, but is lighter, and can be surfaced to the same 1mm center thickness. Trivex rises above polycarbonate with both its optical quality and suitability for drill mounting, however since Trivex is still a relatively new product, availability may be limited.

Finally, when comparing the price of Trivex to polycarbonate, make sure you are comparing apples to apples. If you are looking at an aspheric Trivex product, compare it to an aspheric polycarbonate product; likewise if you are looking at a spherical polycarbonate product, compare it to a spherical Trivex product. You'll likely find the difference to be less than you might think.
I admit, that last paragraph is a little difficult to follow. My understanding is that Trivex is significantly more expensive than Polycarbonate, but may provide other benefits (higher impact resistance, lighter glasses, thinner lenses) that justify the price difference.

Further translations: Polycarbonate lenses may not be as 'clear' (some distortion of the image may be detected), and the frames should provide a heavy, continuous surface because of the relatively lower tensile strength of the material. That last means that an impact may not break the lense, but if the lense is only attached to the frame by a couple of screws the lense may break loose from the frame under impact even if it doesn't break the lense at the point of impact.

Frame-to-Lense construction:

Taking another look in way the three pair of shooting glasses are attached to the bows or frames of the glasses, we can benefit from what we have learned to evaluate the relative 'ruggedness' of the assembly: (Click on the images to see a larger view)

The Claypro is attached to the one-piece lense with two screws, one smaller than the other. There is no other support for the lense. This makes a nice, light pair of sunglasses but based on the above reading) may not keep the lense from breaking loose from the bows.

The Silencio SD one-piece lense is also attached to the bow with only two screws, although they may be more robust than the Claypro because the plastic (Polycarbonate?) material of the frame is 'wrapped' on both sides of the frame. The screws go through the frame, through the lense, and again through the frame. Whether this provides more support to the lense than the Claypro is debatable, but intuitively it would seem to be the case.

The Silencio Nemesis frame is of completely different construction. The plastic (?) frame provides support to the entire top of the frame. There is a nosepiece in the front of the frame, supporting the very narrow section in the center of the lense, which seems to be either glued or otherwise adhered to the lense. The nose supports, on the inside of the lense, is attached to the nosepiece and is between the lense and the face of the wearer. Again, that may provide only marginal support but it may also help prevent the lense from breaking loose from the frame.

Given that the way the frame is attached to the lense may make a difference in the structural integrity of the assembly, it would seem reasonable to assume that the Silencio Nemesis would provide better protection to the eyes and the face from frontal impact.

Getting back to the question of Polycarbonate vs Trivex:

An article from a vendor, ADS Sports Eyewear, provides even more valuable information.

Polycarbonate is virtually indestructible, and it is used exclusively by many of the world's finest sports glasses manufacturers. It is thinner, lighter, and stronger than glass. What's more, polycarbonate lenses can survive a 12-gauge shotgun blast from 10 yards away. (Warning!: If you try this at home, take the glasses off first.)

Polycarbonate naturally blocks almost all of the sun's harmful UV rays. No coatings are required to block UV rays on a polycarbonate lens, so don't let anyone sell you this option.

The strength of polycarbonate is partially derived from its flexibility. It is not brittle and will not shatter. This strength also contributes to its main weakness. Because polycarbonate is so flexible, it is also easily scratched. New lens coatings and hardeners have significantly improved polycarbonate's durability, but choosing a polycarbonate lens still requires an informed consumer. Quality lens treatments match the refractive index of the lens material and allow light to pass directly through. If light passes through the lens coating and the lens at two different speeds, vision will be blurred.


Trivex is a new lens material that is quickly becoming the best thing that has ever happened to sports eyewear. Originally developed for military applications, Trivex is stronger, clearer, and lighter than polycarbonate. Most importantly for sports applications, Trivex minimizes distortion called "chromatic aberration", which is distortion that occurs when objects are viewed away from the optical center.

Chromatic aberration is best measured by its "Abbe value." In prescription eyewear, a higher Abbe value indicates less distortion as your gaze moves away from the center of the lens. Trivex has an Abbe value of 43, while polycarbonate has a value of 30.

Trivex naturally blocks 100% of the sun's harmful UV rays, similar to polycarbonate. Trivex has better scratch resistance than polycarbonate.

Trivex has only been available to the general public since 2003, and is still not offered by most manufacturers as a lens choice. ... Trivex is usually about $25 to $40 more expensive than polycarbonate.

Another point about Trivex, for your general knowledge:


Recognizing the strength of polycarbonate as a safety material for plastics lenses, PPG Industries (Pittsburgh Plate Glass Industries), the originators of CR39 monomer, has introduced its own lightweight safety plastics material known as Trivex'. It is a normal-index material and is claimed to be even stronger than polycarbonate but more flexible, to enhance even further its safety aspect. It offers 100% UV attenuation and is easily tinted by the usual surface dyeing process. Minus lenses can be surfaced down to just 1.0mm centre thickness without the lens losing its inherent safety features. Two lens manufacturers now produce lenses in Trivex" material. Younger Optics calls its lenses Trilogy" and Hoya calls its lenses Phoenix" (PNX). Each company has modified the monomer to its own needs.
In an earlier article, I mentioned that when I bought my latest pair of reading glasses I asked about polycarbonate lenses (which I had specified before) and mentioned that they had been scratched, over time, by the bows when I put them in their carry case. He recommended a new material which they called "Phoenix" ... and reading the above article jogged my memory. I paid the extra expense for "Phoenix" lenses, in a Flexor frame. (This is a light metal frame which completely wraps each lense, and can be flexed over ninety degrees without damage.)

I had wondered if I could use them for shooting glasses, so I could use the bifocular portion of the lense to focus on iron sights and still use the non-corrective 'upper' part of the lense to see objects more than 30 inches away.

The experiment was not as positive as I had hoped. Bifocals tend to be confusing in Action Sports, and while I didn't actually wander around half-lost in a complex Field Problem stage, my shooting wasn't sufficiently improved to make the effort worth the results. There was too much confusing input, being fed to my brain from my eyes, to process as quickly as needed.

Also, it was a sunny day and the reading glasses were clear; I was defeated in the last stage by too much bright sun.

Obviously, a competitor needs at least two pairs of Range Glasses to compensate for different light levels: a smoke or 'dark' pair for bright sunlight, and either a clear or amber pair for low-light conditions, which are prevalent during much of the year here in Oregon.


Polycarbonate lenses are, as stated above, the standard for impact resistant eyewear.
Trivex lenses are even better.

Polycarbonate lenses have been around for several years, and are widely available in a variety of styles, colors, and eyeglass designs. The price of shooting glasses with Polycarbonate lenses will vary based mostly on fashion and trademark. We have seen no evidence that $200 glasses from Oakley, for example, are more effective at protecting your eyes and your face from injury due to impact from small high-velocity fragments.

Trivex lenses have only been available since 2001 (or 2003, depending on your source). They probably are not yet widely available "off the shelf" in your local shooting sports store. At a minimum, they are more expensive. More likely, if you wish to wear impact resistance shooting glasses made from Trivex, you will have to go to your optometrist (or, if you need no optical correction, an optician) and order them custom-made.

When I can buy a pair of Trivex glasses off-the-shelf for no more than twice what I pay for Polycarbonate glasses, I'll make the switch in a heartbeat.

In the meantime, I'll wear only polycarbonate on the Range, and I'll be using the Silencio Nemesis for it's superior rugged design of the frame.

Okay, I'll probably wear the Silencio SD when I lose the Silencio Nemesis . But the Claypro glasses are only for driving, and when I shot Sporting Clays. (Which is never.)

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