It’s a common statement on the range: “I just can’t see the sights anymore.” The problem comes with age, and you don’t have to be retired to experience it. As soon as you notice you need reading glasses, your ability to see iron sights is deteriorating.
As our eyes age, the fluid in them becomes less clear, the muscles that shape the eye to focus get a little weaker, and the iris, the aperture that adjusts for optimum vision in different lighting conditions, gets lazy. All this doesn’t have much effect on our vision under perfect conditions, but it contributes to problems relating to low light and focal distance.
Focal distance is critical when you shoot a gun with iron sights. We begin to have trouble reading the buttons on the remote as we get older, and the front sight seems to grow whiskers. This normally happens in our 40s and can wreak havoc with our ability to shoot well with iron sights.
A good sight picture consists of a sharp focus on the front sight, well aligned in the rear sight, and centered in the target. Even with the eyes of a teenager, the target will lose some of its sharpness due to the eyes’ inability to focus on a close and a distant object at the same time. With good distance vision or corrected vision your eyes will begin to lose the ability to focus in on the close front sight when you hit 40. This may happen so gradually you won’t notice it, but your shooting will suffer noticeably.
Many competitive shooters have known about this a long time, and they often have glasses made with the correct prescription to allow seeing the front sight clearly. I learned this in my mid-40s shooting NRA High Power. I shot a service rifle, and as I got older, I began to have difficulty seeing the front sight. I bought a set of Knobloch shooting glasses and had my optometrist prescribe lenses for them with +.25 and +.5 magnification over my normal distance prescription.
Knobloch glasses allow easy interchanging of lenses, and when it came time to shoot 600 or 1,000 yards, I checked to see which looked best under the existing light conditions. This was tricky because I needed enough magnification to see the front sight well, but I also had to be able to read the 6-foot number board six or ten football fields away. The small amount of magnification made a huge difference and allowed me to call shots in the ten ring, provided I got the wind right.
The same applies to the front sight of a pistol. A sharp focus on the front sight affects, not only accuracy, but the ability to fire fast follow up shots as well. Having your prescription perfect on the front sight will allow you to recover faster.
When the gun fires, the best shooters maintain focus on the front sight through the shot and recoil. Most shooters go through a mental reset, and this often requires a refocus on the front sight, which costs time. If your prescription is optimal, you’ll be much more likely to maintain focus and the process of getting the sights back on the target will happen faster.
The trick in this is to use the minimum amount of magnification to be able to see the sight well. The focal distance should be beyond the front sight as far as is comfortable to still allow the best view of the target. This is called the hyperfocal distance. With the correct focal point, the sight is just inside the near edge of your depth of field, while the target is just inside the far edge.
Normally, you can get by with more magnification in pistol shooting than rifle because the front sight and target are closer. In NRA High Power, the limit is the ability to read the number board. Last year at Camp Perry, I was still able to read the number board at 600 and 1,000 yards with +.75 lenses, but I suspect more magnification would preclude reading the numbers 1,000 yards away.
OK, so now we know what we need for lenses, how do we get the lenses we need? Most optometrists will write you a prescription to your specifications and you can get glasses made to that prescription. Remember, you only need to change your shooting eye. You may want to get lenses made with a couple of different magnification levels, like +.5 and +.75. Using interchangeable lens frames will allow you to match the prescription to your eye and light conditions for the day. You’ll be surprised how easy it is to focus on the front sight and improve your shooting.
Another way to accomplish this is to alter your prescription yourself and order from companies like Zenni Optical. They offer a wide variety of styles and lens colors, and are economical enough to allow you to buy two or three magnification levels and colors to try more/less magnification to give you the best option for the conditions you face.
Having the correct prescription will improve your shooting accuracy and speed and it isn’t rocket science but it is a little math. A little effort in getting your vision right will pay big dividends when you shoot iron sights with a rifle or pistol. It will make you shoot like you’re 20 years younger.
The Science
The actual formula for hyperfocal distance is: H = \frac{f^2}{N c} + f. However, the math to calculate hyperfocal distance is actually quite a bit simpler, since the target is at infinity: It is simply 2x the distance to the rear sight. So if your rear sight is 24 inches from your eye, your hyperfocal distance would be 48 inches.
Diopters powers are inverse focal length, in meters. A 2 diopter lens will focus at ½ meter, a 3 diopter lens will focus at 1/3 meter. Forty-eight inches is 1.22 meters, so to focus perfectly for a pistol, I would want a 1/1.22 diopter lens, which is a +0.82.
Lenses only come in ¼ steps, and you always round down, so you would shoot pistol with a +0.75. You might try a +.50 and a +1.0 and see which works best for you. Light conditions may make a difference in what is optimal.
The author would like to thank Art Neergaard of ShootingSight LLC, shootingsight.com