SHOOTING STRAIGHT
Designing Glasses for the Shooting Sports Enthusiast
By David Lineaweaver, ABO-AC
Release Date: January, 2019
Expiration Date: November 6, 2021
Learning Objectives:
Upon completion of this program, the participant should:
- Understand the unique visual needs of rifle marksmen and hunters.
- Understand the basic considerations for designing eyewear around the particulars of rifle hunting and shooting.
- Understand how to tailor glasses to the specific hunting or shooting needs of an individual.
Faculty/Editorial Board:
David Lineaweaver, ABO-ACCredit Statement:
This course is approved for one (1) hour of CE credit by the American Board of Opticianry (ABO). Technical Level 2 Course SJHI024-2
Avid marksmen, seeking dedicated shooting glasses, may not represent a large portion of those who enter your clinic or optical shop. However, knowing how to advise on eyewear that will perform well for shooting sports builds confidence and loyalty within your customer base. Although there are many common eyewear needs within the shooting sports category, there are too many different types of firearms and shooting venues to adequately cover the specific eyewear needs for each in this course. This course will focus on the eyewear needs of the scoped rifle marksman and hunter (Fig. 1). This course is dedicated to the opticians that strive to maximize optical quality, protection and function in the eyewear worn by marksman and hunters.
WHAT'S IMPORTANT IN HUNTING AND SHOOTING EYEWEAR?
The attributes desired for shooting eyewear are protection, durability, maximized visual acuity, glare and light control, and maximized contrast sensitivity. These same attributes are desirable for "everyday" eyewear, though marksmen have a heightened awareness of the need for these attributes. Let's look at these attributes that are so important to shooting eyewear:
Protection: There are some potential eye injuries to guard against while shooting, such as getting hit in the eye from an ejected casing, or the scope due to rifle recoil. It is helpful to consider the role that frames and lenses play in protection.
Lenses: Polycarbonate and Trivex are the lens materials of choice, due to their superior impact resistance.
The use of glass lenses is strongly discouraged, as glass is the least impact resistant lens material and shatters upon impact.
Frame: An impact resistant frame material in a full frame design with good coverage of the eyes and the area surrounding the eye is important. Larger frames provide a larger area of physical protection. Although obvious, the use of rimless or drill mount frames is discouraged as they do not have the same level of structural integrity and protection as their full frame counterparts.
It is worth mentioning that designing a pair of glasses in a full frame with Trivex or polycarbonate lenses does NOT make them safety glasses. The only way to get prescription safety glasses is to have lenses glazed according to ANSI safety standards in an approved safety frame. I'm not advocating that all shooting eyewear must be safety eyewear, but it is important that opticians know what does and does not constitute safety eyewear so that they can advise their client accordingly.
Quality/durability: There is much overlap between the quality/durability and protection categories. The attributes of quality and durability specifically refers to the strength of the frame, and the scratch and impact resistance of the lenses. Lens impact resistance is a safety concern. However, it is also a quality/durability issue, as maximized vision ends when lenses shatter or break. Scratched lenses can drastically degrade vision, sometimes creating a safety hazard. The author prefers Trivex lenses, as Trivex is more chemically resistant (a drop of acetone on a polycarbonate lens is not a pretty sight!) and provides better optical quality (higher Abbe value) than polycarbonate.
Maximized acuity/sharpness: It is important that the eyewear lenses focus viewed images on the retina as sharply as possible, with as little reflection from the lenses as possible. This may seem obvious, but it bears mentioning. In "everyday life," people are generally happy if they can adequately see what they know and expect to be there. For example, a person knows where to look for road signs (typically a known size, letter color and format) while driving, even before a road sign appears. They only need to read what's on the sign when it comes into view and have enough time to react to or make a driving decision based on that information. Hitting a small target 500 yards away is another issue; you know what you're looking for and about where it is, but you need maximized acuity to clearly see the target for exact alignment of the target in the crosshairs. Hunting is different from both driving and target shooting, as it requires the ability to spot the desired game in unknown circumstances, environmental conditions and locations at any time... quickly!
Frame choice is crucial, though sometimes overlooked when it comes to maximizing acuity. Frame choice influences the weight of the eyewear, which has a direct impact on comfort and the glasses not sliding out of the desired position. Proper adjustment, including vertex distance, frame wrap and tilt angle (especially for progressive lenses), is crucial. Metal frames are generally preferable because of adjustable nosepads. Larger metal frames are a good choice for multifocal lenses, as the seg height can be effectively lowered quite a bit by splaying the nosepads. This range of seg height adjustability provides for an "Everyday" mode that allows the multifocal wearer to work on the computer or read mail without having to tip their head way back. Then, when it's time to go hunting or shooting, the seg height can be lowered, through splaying the nosepads, to "Hunt" mode, enabling the marksman to clearly view distant targets without the interference of the add power. This illustrates why frames with nosepads work best for shooting glasses with multifocal lenses.
Glare/light control: While there are indoor ranges, the vast majority of shooting occurs outdoors. Outdoor environments can present some unpredictable and rapidly changing glare and lighting conditions. To be adequately prepared for these changing lighting conditions will require at least two pairs of glasses (i.e., clear and tinted lenses). To be optimally prepared for the varying conditions often requires several pairs of glasses (i.e., clear, tints of various colors and shades and possibly photochromic lenses). Sometimes sport eyewear with an Rx insert and interchangeable wrap "shields" of various tints work well for this.
Contrast sensitivity: Refers to a person's ability to distinguish an object from its background; it's what makes something pop out from its surroundings. Maximized contrast sensitivity is what allows the hunter to see a stationary deer on a brown hillside. There is much overlap between glare/light control and contrast sensitivity, and key considerations for both are listed below:
Anti-reflective coating: A high-quality antireflective coating is recommended for all shooting and hunting glasses, as it helps maximize visual acuity by reducing lens surface reflections that threaten to reduce contrast sensitivity. Fortunately, the quality and durability of today's anti-reflective coatings are very good. Many marksmen and hunters are already familiar with the benefits of antireflective coatings as they are mainstream now. For those who aren't familiar with the benefits of AR, it works well to describe it as, "a coating on your eyeglass lenses that reduces lens surface reflections, to increase sharpness, just like what's on your scope or binoculars." Unfortunately, some hunters or marksmen may have had a bad experience in the past with an inferior or "old style" anti-reflective coating that scratched very easily, very quickly and very badly. Make sure that you have a good product to offer that is durable, scratch resistant and easy to clean that you stand behind with a good warranty. This is crucial: Do not even offer an AR coating that won't stand up to the rigors of hunting and shooting or that does not come with a good scratch/ defect warranty, as it will only result in frustration for all involved.
Avoid high gloss edge polish: While rolled and polished edges improve the appearance of high minus lenses, a high gloss edge polish can increase unwanted internal lens reflections.
Photochromic: Photochromic lenses can work well as an "all-around" or primary pair of shooting glasses, but NEVER as an only pair. Visual acuity and contrast sensitivity will be compromised, as the timing and intensity of the tint are controlled by ultraviolet light exposure, not the wearer.
Tints: Tints are helpful in controlling incoming light and improving contrast sensitivity. Lenses can be tinted to a wide variety of colors and shades to enhance contrast sensitivity. Neutral density colors like gray reduce light transmission evenly across the color spectrum are usually avoided as they don't enhance contrast. Tint charts abound, but tint preference remains subjective for each patient and situation. Some basic pearls regarding tints for shooting are:
- Yellow, brown and amber lenses have a long history of enhancing contrast in shooting eyewear.
- Brighter conditions require darker tints and lower light transmission while low light conditions require lighter tints and increased light transmission.
- It is unlikely that one tint will deliver maximum performance under all outdoor conditions.
It is helpful to have a variety of "drop-in" tint filters for demonstration. Place the filters behind the patient's current glasses, then let them walk around inside and outside the clinic, to get a feel for how the tint performs. Tint samples also ensure that you and the customer are referring to the same tint color and shade (i.e., when a customer refers to an amber tint, he or she may mean brown, light brown or yellow... or some combination thereof).
Polarized: Polarized lenses also improve contrast and are great at reducing glare off of water and other highly reflective surfaces, due to the polarizing filter.
VIEWING THE TARGET
Prescription correction for target shooting or hunting is ALWAYS distance correction. This is an important concept, as sometimes a marksman will request "special" glasses, specifically designed for viewing certain distances (50 yards, 100 yards or 500 yards, etc.). The "standard" distance correction will work for all targets at all distances. The marksman may be wearing multifocal glasses, but the target (bull's-eye, game or can on a fence post) is always viewed through the distance portion of the lens.
Rifle: Targets are viewed with a scope or open sights.
Open or "iron" sights: Adjustable rear and front sights on a rifle, that the marksman aligns together and centers on the target. The sights are referred to as "open," as they are not encased in a scope and do not produce any magnification.
The rifle scope in Fig. 2 shows a telescope mounted on top of the rifle that has an internal reticle, which the marksman uses to center the crosshairs exactly where he wants to shoot (on the target). Scopes have horizontal (windage) and vertical (elevation) adjustment knobs, called turrets, that can be adjusted to align the marksman's line of sight with where the bullets are hitting on the target. The marksman refines the alignment through a process of firing at a target (usually at 100 yards) and then making adjustments to "tighten" the shot group. Some scopes have a knob to adjust parallax, which we'll discuss shortly. The magnification of the scope can be fixed but is often variable, commonly from 3x to 9x. It also reduces the chance of being struck in the forehead by the scope, due to recoil, after firing (from eye relief that is too short). The scope is an afocal magnifying device, meaning that there is not a refractive interaction between it and the marksman's prescription eyewear. Eye relief is the distance between the eyepiece of the scope (lens closest to the marksman) and the marksman's eye or eyewear that allows for a full unobstructed "viewing window." Maintaining proper eye relief also reduces the chance of being struck in the brow by the scope, due to recoil, after firing (from eye relief that is too short). Eye relief is designated by the manufacturer and is often around 3.5 inches. There is a range (closer in or further away from the specified eye relief) that will still render a full unobstructed view, which is referred to as the eye box. In addition to proper eye relief, there must be centered vertical and horizontal alignment between the eye, the scope and the target to ensure a "full window" view.
Field of view (FOV) is defined as the measurement of distance you can see from edge to edge through the optic, when properly aligned to have a "full window" view (Fig. 3). Field of view decreases as magnification increases. It is important to keep in mind that field of view is a function of optics and separate from the concept of a "full window" view.
If any part of this view is obstructed, it is referred to as vignetting (Fig. 4). Vignetting is resolved by the marksman adjusting his or her head position to get a centered alignment between the eye (looking through distance correction), the scope and the target, and adjusting eye relief to the amount designated by the manufacturer. Exaggerated movement of the crosshairs on the target, can occur due to slight body movement (breathing, etc.) or poor support of the rifle. This must be differentiated from parallax, which we'll discuss shortly. Vignetting, decreased field of view and exaggerated movement of the crosshairs becomes more difficult to avoid as scope magnification increases.
Parallax: The scientific definition for parallax is very technical and not all that helpful for understanding how this phenomenon can affect shooting accuracy. For our purposes, it is an apparent change in the location of the crosshairs, relative to the marksman's head or eye position. Parallax can cause a shot to be off the mark, even though the crosshairs appear centered on the bull's-eye.
To check for parallax, view a distant target and place the crosshairs on the bull'seye. Move your head or eye position just slightly; if the crosshairs don't appear to move, congratulations! You're parallax free. If the crosshairs do appear to move, parallax is present. Parallax can largely be resolved by ensuring the marksman is viewing directly through the center of the scope and making sure that he or she has a full view, as opposed to a vignetted view.
Ensuring that the scope view is parallax free will go a long way toward placing the shot exactly where you want it. Parallax becomes more of an issue with higher magnification and longer distances. Long range competitive marksmen often have a parallax adjustment, for various distances, on their scopes. It is helpful to understand parallax, but also understand that it is always a magnification/marksmanship issue, it is never an eyeglass issue.
CASE STUDY
Jim was a 48-year-old rancher who enjoyed recreational shooting with family and friends. He was fairly good at this and hit his share of bull's-eyes. Recently he decided to go deer hunting with some friends, which he hadn't done before. Good-natured Jim came into the clinic, frustrated that he couldn't see the game that his friends saw. He also wisely declined a shot when the view through his scope was blurry. Jim's exam from two months ago revealed that he had no ocular pathology and achieved 20/20 distance acuity with the following prescription:
OD: +2.00-1.00 X 092
OS: +2.50-1.25 X 075
Add: +1.75
Photo gray progressive lenses were glazed into the same full metal frame choice which Jim had selected for his last five pairs of glasses. Jim had long been happy with single-vision distance photo gray lenses, due to superior scratch resistance, optical quality and photochromic action, but now he couldn't read or do near work with his distance glasses. He seemed to be adjusting well to the progressive lens style and wore them while performing all his ranch tasks and even recreational shooting. After further discussion, it came out that Jim had difficulty quickly acquiring a clear view through his scope while in various positions (especially in the prone position). He said that he would have to move his head and "fish around" to find the "sweet spot" in the lens to see clearly... and by then his chance was gone.
Jim is very frugal and did not want to invest in several "specialty" pairs of shooting glasses, though we discussed the benefits of multiple pairs for specific conditions. We talked some more and hammered out a remedy that was less than optimum but would increase Jim's chances for success in the field. Here's what we came up with:
- Same full metal frame as he is accustomed to
- FT bifocal Trivex lenses
- Yellow #2 (50 percent) solid tint
- High-quality AR coat, with one-year scratch/defect warranty
The fitting height was placed very low in the frame so as not to interfere with distance vision, in any circumstance. He mainly needs distance correction, and the brief manual lifting of his frame to see up close works fine for his purposes. His progressive lenses work well for tasks other than hunting. The yellow tint provided good contrast and the antireflective coating sharpened vision by reducing lens reflections. The lenses on Jim's hunting glasses were scratched at the end of hunting season, but they had performed well, and he filled his tags. The scratch warranty covered replacement of the lenses, and Jim is happy. He is considering a pair of brown-tinted "hunting" glasses for brighter days, in addition to his everyday progressive pair and his yellow tinted hunting glasses for the next hunting season... and so the appreciation of multiple pairs begins!
Hunting, marksmanship competition and recreational shooting provide the opportunity to practice and enjoy a sport, the outdoors and the company of family and friends. Opticians could benefit from taking a hunter safety or basic gun safety/marksmanship course to get a better understanding of the principals of marksmanship and the unique visual needs of marksmen. This will enable them to design shooting eyewear that meets and exceeds the wants and needs of the marksman... and maybe develop a new interest in the process.
