Greetings Shooters,
Through the Bullsyeye-l@lists.lava.net website, Roddy had discussed great shooters of the past using iron sights entitled, "Blast from the Past......Scores." Rest assured, these elite shooters had perfected their focus. My friend Ross, who is not presbyopic, had problems seeing his iron sights in a recently attended "Two Day NRA Three Gun Pistol Shooting Clinic" at Richmond, Virginia in which Brian Zins was one of the coaches and Jerry Keefer provided technical information. Ross was informed that if the sights were misaligned by the thickness of a business card, this would then be equivalent to 2.4" at 50 yards. The coaches talked about being so focused, they could see little defects on the front sight. Jack had mentioned that although he can see the front iron sight with the aid of a lens, keeping focused for any length of time was difficult. Ed discussed with me that he noticed changes in his "aiming ability" with his eyes as he tries to focus onto the iron sight. Ed, of course, is an extremely astute observer and was able to convey to me one of the visual principles known as PHORIA, which I'll be discussing. Camp Perry is just around the corner and it's never too early for us to hone up on our skills for the upcoming ball matches for those of us who do not regularly shoot with iron sights. The topic of interest is, "Keeping Focused."
When we look at a close object, three things happen which is known as the "Triad." The triad consists of accommodation, convergence and decreased pupil size. Accommodation is the ability to change distance focus to near focus. We have a certain amount of focusing ability depending upon our age, easy when we are young, more difficult as we become older and almost impossible at ages 60's and above. As we accommodate, our two eyes converge inwards so that each eye is pointing to the close object. Simultaneously, our pupils diminish in size. These three things happen smoothly and effortlessly for most of us, but not all.
Accommodation and Convergence:
When we get new eyeglasses, the distant part of the lens will allow our eyes to have a "resting focus" at infinity. This is the upper portion of the lens if we have bifocals or progressive lenses. When we get lenses for the iron sight, our "resting focus" will now be at the front iron sight. What this means is that we do not have to struggle with refocusing our eyes when the lens does its job. Both eyes cannot see the front and rear sights simultaneously so we must use only one eye, typically, the dominant eye. Essentially, we are disrupting the natural binocularity of our eyes.
When we see the front iron sight clearly with the use of the proper lens, we no longer need to converge our eyes. Some may need an occluder for the non-shooting eye while others have developed "suppression" in their non-shooting eye and not need an occluder as they keep both eyes open. Since we know that the front iron sight is in close proximity, there is a tendency to want to converge our eyes. If one converges the eyes, the eyes will then try to accommodate. If the front iron sight was already clear (with the use of a lens for us older presbyopic shooters), the extra accommodation caused by the convergence may now blur the front iron sight. This may be one of the reasons why the front sight goes in and out of focus.
The best way to avoid this extra accommodation is to use a plus lens of sufficient magnitude and not use such a low lens power that it does not clear the front sight properly. Granted, the bull will be blurred, however maintaining focus will be easier and aligning front and rear sights is the key for good scores. If the power of the plus lens is too low, then we will try to compensate the extra focus needed with our own accommodation and this can lead to fluctuating focus. All this relates to how well we maintain focus onto our iron sights. Remember, younger shooters who do not need prescription shooting glasses will see the bull equally blurred if they focus onto the front sight properly.
Pupil Size:
Since there is no way we can control our own pupil size effectively, we can use use various makes of apertures to help further refine our focus. Decreasing the size of an aperture will extend our depth of field, thereby allowing simultaneous clear focus for the front sight, rear sight, and the bull as well. On the downside, we need to carefully position our line of sight to view through the aperture, a little challenging as we're shooting sustained fire. Since the apertures are adjustable, you will be able to fine-tune the opening for the best compromise.
Apertures that attach to your eyeglasses with a clip may not fit because of shape and size of your eyeglass frame and the thickness of your lenses. Nose pad arms on metal frames may further hinder a good fit as well. A consistent fit may not be possible for some. Apertures with suction cups would eliminate these problems but care must be taken to avoid scratching your lenses. The suction can fail and the aperture may pop loose during an inopportune time such as during rapid fire in a match. My best advice here would be to borrow a friend's aperture before buying your own, the cost being around $50 to $80.
Phoria:
Just as the eyes have a "resting focus," our eyes also have a "resting aim" known as the PHORIA. Often, our eyes may not normally have a "resting aim" at the object we are observing. What I mean by this term is best described by an example. If we are looking at the bull at 50 yards, our resting aim could be inwards or outwards, but we then must force our two eyes to point at the bull.. A crude example would be a car wheel alignment with a toe-in or toe-out problem. If the resting aim is way off, then we may see an individual with a "crossed-eye" (esotropia) or a "walled-eye" (exotropia). If the resting aim is slightly off, then we normally re-align our aim by forcing our external eye muscles to help point our eyes at the object we are seeing.
A simple way to test your own resting aim is to stare at a small object at 20 feet and cover your right eye with your right hand. Quickly uncover the right eye and now cover the left eye. Note if there was any motion to this object. If the object moved to the left, then the resting aim of the right eye is outwards. If the object moved to the right, then the resting aim is inwards. Repeat this alternating cover several times and you may note the movement of the object to widen, representing that you are reaching your maximum resting aim. Next, try this again at an object approximately 2 to 3 feet away. Again note the movement when you switch your hand from one eye to the other. Some may notice a vertical displacement as well. If there was no movement whatsoever, then your resting aim is perfect for the distance you are viewing. If there was movement, then your external eye muscles must pull to align the eyes to avoid double vision.
By occluding the non-shooting eye and using the best plus lens for "your" eyes, you will have the perfect iron sight picture as long as you allow your non-shooting eye to "drift" to its natural resting position and not try to converge your eyes. Those who shoot with both eyes opened must avoid converging also. Younger shooters who are not presbyopic will also benefit with the plus lens if keeping focus is difficult. The plus lens is a must for all older shooters.
Holding breath and oxygen deprivation would be a good future topic for its effects on keeping focused but getting the correct lens should be the first concern. Please refer to the front magazine cover of the January 2005 issue of Shooting Sports USA. This picture of the seven time national police shooting champion, captioned, "Shows his match-winning form," will help summarize some of my points. Note that the shooter in the featured front cover is right eye dominant so he aligns the sights with only his right eye, and allows his non-shooting left eye to drift to his "resting aim" which is outwards. In this case, he then suppresses vision from his left eye to avoid double vision rather than using an occluder. (Police shooting is an entirely different discipline than bullseye shooting but I wanted to use this picture for illustrative purposes)
Shooters of the ball matches at Camp Perry participate on an equal playing field in that we all must use comparable ammo and ball guns. It is my hope that we also "see" our iron sights well so that qualifying for the President's Hundred will have a new meaning because I suspect that a large percentage of shooters struggle with their focus judging from the number of messages I receive. We can be sure that the top hundred shooters see their sights fairly well.
Good luck and see you at Camp Perry!
Norman H. Wong, O.D.