Vision Issue

[EdStevens]

In my experience, the amount of the rear sight gap also plays a part, especially in dimmer ambient light conditions.

If the rear sight gap is too narrow, it becomes more difficult to focus on the front sight. I may be able to clearly focus on my wrist, for example, which is much closer to my eye, but may not be able to focus on the front sight when looking through the rear sight even though it's farther away from my eye, because of the effect of looking at the sight through the gap.

So increasing the gap of the rear sight may make it easier to focus on the front sight; but it also makes it more difficult to maintain a good sight alignment and group size can increase as a result.

[ModestoPete]

Ed, I have had the same issue. Thanks for your solution.

[ShootingSight]

Your eye is not going back/forth from the target to the front sight. If you set it up right, you can see both in focus at the same time.

This is the concept behind depth of field.

I often hear people who do not understand optics explaining how the eye can only focus at one distance at a time, and this is simply not true. Yes, there is only one theoretical perfect focal point, however you also have to consider what is defined as 'perfect focus'. Since the photoreceptors on your retina are individual cells, when you look at an image that has a sharp edge, that edge will not fall exactly between cells, such that one call sees black, and the adjacent cell sees white, so the limitation of focus is that unless the width of the blur line for an image exceeds 2 cell diameters, your brain cannot detect any blur. Thus if you take an object that is at your eye's perfect focal point, and displace it either closer or further from that perfect focal point, it is not in theoretical focus, but it's blur is below the detectable threshold of the retina, so it appears in perfect focus. This is the genesis of a depth of field. For the human eye, it is considered that the smallest blur that is detectable is about 1 MOA, and this is the source of the 20/20 vision test. When you look at an eye chart, all the characters are 5MOA x 5 MOA, and when you get something like the letter E, this is 3 black horizontal lines, separated by 2 white lines, each line is 1MOA wide. If your eye can see the individual lines instead of a grey blob, this means the width of the blur is less than 1 MOA, and you have 20/20 vision. 20/15 means you can resolve 0.75MOA.

This range then gets bigger when you consider that even with a slight amount of blur, your brain can still estimate where the edge of a line is. This ability to estimate diminishes as the blur line gets bigger.

So, optically speaking, if you had sufficient depth of field, you can get both the target and the front sight in focus at the same time by centralizing your focal point between the target and front sight, thereby limiting your blur on either the target or the front sight, and allowing your brain to best estimate where the true edge lies. If you focus on the front sight, you putt all the blur on the target, and your brain loses the ability to estimate the edge of the target. You can still estimate center of mass, but if you are shooting 6 o clock hold, determining the edge of the target is more accurate.

Question then simply becomes where you focus to centralize your depth of field, and how to maximize your depth of field.

The first is to focus at the front sight hyperfocal distance, and doctors do operate to this level of precision, and the second is to use as small an aperture as possible, because a smaller aperture increases your depth of field.

What I am proposing is not much different than what a lot of pistol shooters preach. It's just that they came to the conclusion empirically, by trying different things, while I came to the conclusion by deriving the formulas and doing the math.

Having your eye focus at 1.5 to 2.0 meters gives you a good front sight and a good target. This is why Knobloch sells stock lenses in the 0.5 to 1.0 range, because that is the greatest demand. My only add here is that the optimal distance can actually be calculated as 2x the distance from your eye to the rear sight, to satisfy the hyperfocal equation .... and the answer usually works out to somewhere between 1.5 to 2 meters, agreeing with the generally accepted answer.

[scerir]

If you set it up right, you can see both in focus at the same time.

Personally I have both the front sight and the target in *perfect* focus at the *same* time. Unfortunately this gives no help to me, because the sharp image of the target is very distracting, and the smooth trigger release (independent of the relative movement between front sight and target) becomes much, much, much more difficult. S.

[Spencer]

Your eye is not going back/forth from the target to the front sight. If you set it up right, you can see both in focus at the same time.

This is the concept behind depth of field.

I often hear people who do not understand optics explaining how the eye can only focus at one distance at a time, and this is simply not true. Yes, there is only one theoretical perfect focal point, however you also have to consider what is defined as 'perfect focus'. Since the photoreceptors on your retina are individual cells, when you look at an image that has a sharp edge, that edge will not fall exactly between cells, such that one call sees black, and the adjacent cell sees white, so the limitation of focus is that unless the width of the blur line for an image exceeds 2 cell diameters, your brain cannot detect any blur. Thus if you take an object that is at your eye's perfect focal point, and displace it either closer or further from that perfect focal point, it is not in theoretical focus, but it's blur is below the detectable threshold of the retina, so it appears in perfect focus. This is the genesis of a depth of field. For the human eye, it is considered that the smallest blur that is detectable is about 1 MOA, and this is the source of the 20/20 vision test. When you look at an eye chart, all the characters are 5MOA x 5 MOA, and when you get something like the letter E, this is 3 black horizontal lines, separated by 2 white lines, each line is 1MOA wide. If your eye can see the individual lines instead of a grey blob, this means the width of the blur is less than 1 MOA, and you have 20/20 vision. 20/15 means you can resolve 0.75MOA.

This range then gets bigger when you consider that even with a slight amount of blur, your brain can still estimate where the edge of a line is. This ability to estimate diminishes as the blur line gets bigger.

So, optically speaking, if you had sufficient depth of field, you can get both the target and the front sight in focus at the same time by centralizing your focal point between the target and front sight, thereby limiting your blur on either the target or the front sight, and allowing your brain to best estimate where the true edge lies. If you focus on the front sight, you putt all the blur on the target, and your brain loses the ability to estimate the edge of the target. You can still estimate center of mass, but if you are shooting 6 o clock hold, determining the edge of the target is more accurate.

Question then simply becomes where you focus to centralize your depth of field, and how to maximize your depth of field.

The first is to focus at the front sight hyperfocal distance, and doctors do operate to this level of precision, and the second is to use as small an aperture as possible, because a smaller aperture increases your depth of field.

What I am proposing is not much different than what a lot of pistol shooters preach. It's just that they came to the conclusion empirically, by trying different things, while I came to the conclusion by deriving the formulas and doing the math.

Having your eye focus at 1.5 to 2.0 meters gives you a good front sight and a good target. This is why Knobloch sells stock lenses in the 0.5 to 1.0 range, because that is the greatest demand. My only add here is that the optimal distance can actually be calculated as 2x the distance from your eye to the rear sight, to satisfy the hyperfocal equation .... and the answer usually works out to somewhere between 1.5 to 2 meters, agreeing with the generally accepted answer.

Sigh!

[David M]

The Pistol sight picture should have a sharp foresight. The target and the rear sight will have a slight blurr.
If you can see both a focused foresight and target your eye is focused too far down range and has a rapid focus change between the foresight and target, it is your brain that is interpreting both images but this leads to eye fatigue during a match. It also gives poor rear sight alignment.
The best lens to try is +0.5 to +0.75 over your normal distance script. It means your relaxed focal length of 1-2 metre in front of your foresight.
When you bring the sight up into your line of vison your eye will focus (without too much strain) on the foresight.
The front sight should be approx. the width of the black. It is a perceived image that also will change with light levels as well as arm lenght, distance, barrel length, glass lens etc.
Try different width sights on each pistol and vary the rear sight width to suit the ambient conditions.