Sights and Sighting in the N-SSA

This is the sixth of a series of articles, reprinted with permission, from "The. Black Hat," newsletter of the 6th Wisconsin Infantry.

Skirmishers and Vision Problems

Perhaps the most common vision problem suffered by skirmishers results from a change of the near point in the aging eye. The near point is defined as the closest point to the eye at which it can see a clear image. With normal vision, even for older competitors, and even if vision must be corrected by glasses, the competitor can see clearly from the near point to infinity, within the limits of normal vision. For the young person the near point should be in the range of four to seven inches from the eye. However, with advancing age the near point increases in distance from the eye; for most of us it will pass the point where we can see our rear sights well, and it may pass the point where the front sights of carbines, rifles, and muskets can be discerned clearly.

The change in near point starts for all of us while in our forties, and continues to worsen as years pass. Figure 1 is a rough illustration of the eye. including the cornea, lens arid retina. The cornea functions as the first lens in the eye, beginning the refraction (bending) of light which is necessary to focus the light on the retina. the light must be focused precisely at the retina for good vision. The lens also retracts the light entering the eye, but is adjustable to allow us to focus on objects at different distances. It is adjusted by muscles and tendons in the eye without a conscious effort on our part. To provide clear vision of an object close to the eye the lens must adjust from the flatter shape required for good distance vision to a more pear shaped configuration. Figure 1-a illustrates the eye focusing on a distant object; 1-b on a closer object with a properly functioning lens; and 1-c on a closer object with the older, less flexible lens. Note in 1-c that the light is focused at a point behind the retina.

The change in near point occurring with age results from an increasing thickness and stiffness of the eye's lens. In the aging, the lens cannot make the required shape change to provide good close up vision.

One's near point can be determined by moving a sheet of paper with small print slowly away from the eye until the print becomes clean If the near point for your shooting eye is greater than the distances to the sights on your firearms you will not be able to see the sights well without using an aperture sight or some type of optical aid.

Figure 2-a illustrates the area of clear vision for a young rifle or revolver competitor. For this competitor the near point is closer to the eye than the rear sight, and he can see the rear sight, the front sight and the target well. The young competitor can use an open sight, and align the sights accurately while achieving a clear vision of the target. Some sources state that the eye cannot truly focus at three points simultaneously, but the lens can change shape rapidly enough to provide information to the brain which permits it to provide a clear vision of both sights and the target.

Figure 2-b illustrates the area of clear vision for a competitor with aging eyes (actually mine). It shows the distance from the aiming eye to the rear and front sights on the rifle used for competition. The rear sight is at approximately 11 inches and the front sight is at 39 inches. However, my near point is at approximately 30 inches, too great to be able to see an open rear sight well. However, I can see the front sight well on my rifle (but not on the carbine which has a sight about 28 inches from my right eye).

Figure 2-c shows one solution for vision problems that many competitors share. In this figure the rear sight is an aperture or peep sight. Under ideal conditions the aperture sight provides two important advantages:

It provides good depth of field (good vision of the sights and the target). Since the only light which enters the eye does so near the center of the cornea and lens, the lens does not have to change its shape to focus the light on the center of the retina. With the aperture sight the older, less flexible lens, can provide good vision of objects close to the eye and good distance vision.

It provides better vision of the target. Ideally the aperture sight focuses light at the center of the retina. Even for those with excellent vision there is a small improvement in vision resulting from concentrating light only on the center of the retina. Some sources suggest that by careful positioning of the head and sighting eye, a competitor can further improve his visual acuity.

However, there are some problems with using the aperture sight:

The small aperture sight may not provide enough light to the eye for good vision. This problem is aggravated with age because the eye becomes less efficient at processing light; and if the eye does not receive enough light, only an indistinct image is discernible. To some extent this problem negates the advantages of the aperture sight for older competitors.

On a sunny day a very small aperture may provide excellent depth of field and provide enough light to the eye for good vision of the target. Paper targets are more easily seen with an aperture sight than are the breakable targets in the team events. The white background of the targets reflects more light to the eye than any other type of target. However, under low light conditions (overcast sky, smoke, light rain, etc.) and conditions of poor contrast between the target and background, the same aperture sight that works fine in the individual matches may not provide adequate vision of the targets for good team event marksmanship.

The problem of providing enough light to the eye with the aperture sight can be aggravated by using dark (green, gray, red, blue, brown) shooting glasses. Dark glasses which reduce the light entering the eye can make a poor vision situation worse. If a competitor uses dark glasses with an aperture sight on bright days, he should try using clear or amber glasses under low light conditions.

N-SSA firearms do not locate the rear sight close enough to the skirmisher's eye to permit the aperture sight to be used effectively. Aperture sights on modern rifles are normally placed at a distance of two to six inches from the eye.

At a location close to the eve, the aperture can be small enough to permit only a small diameter stream of light to enter the eve. A small diameter stream of light is important to obtain the advantages of improved vision and improved depth of field.

On the firearms used in musket and carbine team competition the rear sight is located ten inches or more from the eye. On these firearms there may be a compromise required in the size of the aperture providing one small enough for good depth of field (and clear vision of the sights) and still permitting enough light for a clear vision of the target. The aperture size can be quite large and still provide some benefit for the competitor. It is best when preparing an aperture sight to start with a small hole and experiment to deter-mine how large it should be. Some skirmishers use one sight with a small aperture for sunny days and a second sight with a larger aperture for poor conditions.

At the distance from the eye on N-SSA firearms, aperture sights do not provide a large field of vision. The limited field of vision may be adequate for paper targets, but for the team events it may cause difficulty. I occasionally shoot at the wrong target on the hanging events because of this.

(Civil War firearms do not permit the centering of the sighting eye precisely behind the aperture to obtain the improvement in vision of the target mentioned earlier. These firearms would require adjustable stocks to center the eye behind the sight. In addition, the failure to position the eye correctly behind a small aperture sight can lead to a flattening of one side of the bull on the N-SSA target. It also can cause a similar problem with the targets we shoot in the carbine and musket company matches. This problem is discussed in more detail in Position Rifle Shooting.

Several of the problems using the aperture sight can be eliminated by using an aperture placed near the eye (attached to the glasses) and open sights. The aperture attached to the skirmisher's glasses can be smaller than the aperture in a rear sight and provide good depth of field, clear vision, and a wide field of vision. This option is illustrated in Figure 24.

There are several ways of providing an aperture near the eye. Many skirmishers use the Merit optical device. It consists of a rubber suction cup for attachment to one lens of the shooting glasses and an adjustable iris. The device can be precisely adjusted to locate the opening of the iris, and the opening size can be adjusted over a wide range.

Other skirmishers use simpler devices attached to the glasses. They include various devices designed for revolver shooters, a strip of electrician's tape, or a strip of thin sheet metal. All of these devices must. have a small hole positioned at the correct location for use with the shooting eye. The common problem with all of the aperture devices is obstruction of vision while not actually sighting. However, many skirmishers use them; apparently they find the advantages of better vision outweigh the inconvenience.

Another helpful solution for visual problems is the use of an over-plused lens. The over-plused lens is not a corrective lens, but can be used by the shooter who has good vision or good vision in the shooting eye with a corrective lens. The term over-plused lens derives from the use of an additional plus diopter lens or a plus diopter prescription change to improve close vision. The near vision portion of bifocal glasses are a plus diopter lens.

The plus diopter lens provides improved Vision of the sights, but causes some loss in clarity of the target. (Figure 2-e illustrates this situation). As the lens strength is increased the point at which clear vision begins is moved closer to the eye; but the visibility of the target decreases. The over-plused lens is more common for revolver competition than for rifle competition since the distance of the revolver sights from the eyes is relatively long (at arm's length) and the revolver target is generally closer than that of the rifle.

The over-plused lens may be incorporated into the shooting glasses as a prescription change or maybe an extra lens that is worn between the shooting glasses and the target.

The Clearsight optical device Is a means of adding the extra lens without changing one's shooting glasses. It attaches Securely to the frame of the glasses, and positions the extra lens near the center of one lens of the shooting glasses. The central position of the lens is correct for revolver shooting but not for rifle shooting. Three small lenses of various diopters (a measure of refractive power) are provided with the device. The shooter experiments with the lenses to find which best suits his needs.

The optical device must be modified to locate the lens at the correct position for use with the rifle. It also must be modified to prevent the lens from being moved out of position by recoil. In spite (if the difficulties in using the device for rifle shooting, many skirmishers use it for this purpose. Perhaps someone will offer a similar device designed for rifle competitors.

I have used the Clearsight optical device for revolver shooting with good results. It is available from Clearsight Products, 1501 39th Street, West Palm Beach, Florida, 33407, phone (407) 840-,666.

An important plus for t he Clearsight optical device (compared to an aperture attached to the glasses) is the unobstructed vision; it does not obstruct vision to the extent of an aperture device. However, as noted earlier it does not provide the depth of field of an aperture located on the shooting glasses.

The over-plused lens may be incorporated into the shooting glasses by replacing the entire lens over the aiming eye with the modified prescription, or it may be added to the prescription used in a bifocal lens or trifocal lens. Several sources give guidelines for adjusting the prescription, but a skirmisher will probably have the best results (as I have) by explaining his vision problems and desires to an optician.

A right-handed rifle shooter could have the prescription added to the entire right lens, or have it added to the upper left corner of the lens. A right-handed revolver shooter could have the prescription added to the lower half of the right lens or added to the center of the lens.

I use shooting glasses for revolver competition with an over-plused lens prescription in the bottom half of the lens of the shooting eye. With this lens I cannot see a revolver target clearly, but the revolver sights are very clear. I can use the same glasses for rifle shooting by looking through the top left corner of the lens.

It may be helpful for the skirmisher to combine some of the sighting aids to solve his vision problems. It is possible to use an aperture on the glasses with an aperature sight or to use an over-plused tens with an aperture sight.

 Scanned from the November-December 1997 issue of The Skirmish Line. Graphics omitted.