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Home » Shooting Glasses » Shooting Articles by Dr. Nolt » The Specs on Shooting Glasses

The Specs on Shooting Glasses

Do you wear protective lenses when shooting? Walking through the bush, bench rest shooting and black powder shooting all have the potential for serious eye injuries and in activities such as skeet and sporting clays, where targets are incoming, shooters are often bombarded with fragments of clay targets. Fragments from these types of projectiles can cause corneal abrasions, or foreign bodies embedded in the cornea or conjunctiva. This can lead to serious problems with infection if not treated promptly. The best way to avoid these problems is to wear protective safety lenses. Indeed, any person who is involved in shooting sports should wear optically correct ophthalmic quality protective eyewear for physical protection and protection from ultraviolet radiation.

But careful choice of eyewear is important because such factors as the type of lens, frame design and fit all contribute significantly to a shooters performance.

The lenses for shooting glasses are made from three materials: crown glass (which can be heat treated), CR 39 plastic and polycarbonate (both of which can be anti-scratch coated). In terms of the best safety lens, polycarboante ranks at the top, followed by CR39 and then heat treated crown glass.

Today 90% of all prescriptions are filled with CR 39 anti-scratch coated lenses. Both the CR 39 and polycarboante lenses are less than half the weight of glass lenses.

It makes sense to use either of these lens materials in a pair of shooting glasses. Polycarboante material has outstanding impact resistance, but it must be handled carefully in the uncoated form to prevent scratching. Polycarbonate lenses are also more expensive than CR 39 because they require special handling techniques and machines to generate the curves, edges and tint. This leaves CR 39 with anti-scratch coating as the material of choice for your shooting glasses.

Protection from ultraviolet radiation should also be a concern, especially with our depleteing ozone layer. Ultraviolet radiation causes keratitis, an inflammation of the cornea commonly known as ”snow blindness”. It contributes to the development of cataracts and has been shown to cause degeneration of the retinal pigment epithelium.

Recent studies have also linked exposure to UV radiation with an acceleration of age related macular degeneration. This is a major cause of blindness in North America today.

UV radiation can also cause tumors of the eyelid, such as basal cell carcinomas, which require surgical removal. A malignant melanoma will be fatal in almost all cases.

Do I have your attention? Protection from UV radiation is important.

Many quality sunglasses do block UV radiation but clear lenses may also be made with UV protection. We have all heard and read advertisements about blue blocking lenses. Are they useful.

The theory behind them is good. The lens is supposed to block the shorter wavelengths of light which are scattered more by fog and mist. If we eliminate the shorter blue wavelengths, it should enhance our vision on foggy overcast days. But the selective absorption of these lenses make it difficult for some people to differentiate red from green while driving.

These lenses also negatively affect your depth perception so that red lights, for example, may appear nearer or farther away than they actually are. The physiological optical term for this is chromostereopsis.

What if you are wearing a ”blue blocking lens” while driving home at dusk and a man wearing a blue jacket is walking down the road? Remember the blue wavelengths of light are blocked by these lenses. You would probalby not see this man as soon as you would if you were wearing a clear lens.

So what is the best type of lens to use for protection from UV radiation?
For low light conditions the best lens is clear with an anti-reflection coating. The UV filter is included with these lenses. The amount of light transmitted through a clear lens is 92%. Eight percent is lost to reflection.
The AR coating increases the amonut of light transmitted to 99%. The 7% increase in the amount of light transmitted is within our just noticable difference threshold. This means that the human eye can notice the change in light transmitted.

AR coatings are found on all camera, rifle and binocular lenses for this reason. AR coatings are more expensive and worth every penny!
Another advantage to AR coatings on spectacle lense is they eliminate ghost images that are noticed at night.

The UV filter is essential because it blocks wavelenghts of light under 400 nanometers.

AS far as tints are concerned some people see better with a light yellow at dusk and dawn. The psychological reason for this is we associate yellow with sunlight and objects appear brighter with a yellow tint. Scientificaly the yellow tint filters out the short UV wavelenghts of light; which are scattered more at dusk and dawn and under rainy overcast days. Filtering the shorter wavelenghts of light improves visual acuity under ther conditions.

For sporting clays, skeet and trap under moderate to bright light the most popular tint is light medium target orange. (LMTO) This tint transmit more of the orange wavelenghts of light to your eyes and improves target contrast.

Tint preference is personal. A comfortable tint for one person may be totally unacceptable to another. A good choice of lenses would be clear with an AR coating for low light and a pair of LMTO for other light conditions. These lenses are useful for pistol, rifle, shotgun, archery and hunting in general.

Shooting sports, especially shotgunning require spectacle frames desighned for shooting. When your shotgun is mounted and head is on the stock the eye becomes the rear sight on the shotgun.

Dress frames are not designed for shooting. With a dress frame you are looking through the top portion of your lens or even through the eyewire. This induces unwanted prismatic effect and the position of the eyewire decreases your ability to pick up targets quickly.

The people who make and market shooting glasses know about these problems and they design frames for shooting. These frames sit high on your bridge so when your head is down on the comb of your gun your eyes are looking through the optical centers of your lenses. These frames are available with adjustable bridges that enable you to adjust the vertical position of the frame to your face. They are available with interchangeable lenes so you are able to switch lenses easily to match ambient light conditions.

Other important features include rubber covered cable temples, silicone nose pads and sweat bars. Impact resistant cases with storage for extra lenses, cleaning cloths and belt clips are included. Add up the features and the result is a frame that is designed specifically for shooting.

If you need prescription lenses to correct for small amounts of nearsightedness, farsightedness or astigmatism this correction should be ground into your lenses. The improved visual acuity will enhance depth perception, reduce tiredness and help track moving targets.

Properly fitted prescription eyewear will sharpen your vision and provide eye safety for all shooting sports.

If you have any questions please e mail me at: bnolt@telus.net

Published: 7/1/1994
Source: Western Sportsman