Please educate me on this subject.
If the light is bright, one can use +0.5 or even less diopter. That is because in bright light, pupil constricts, the depth of field is wide.
But as the light diminished in outdoor, the eye pupil will dilate, the depth of field is narrowed. So to focus on front sight in darker lighting, diopter has to be more precise on the front sight. So the diopter will go up to +0.75 or even +1.0 (if you still can see the target).
So darker the light, higher the +diopter (+0.75 or +1.0); brighter the light, less stringent the requirement due to pupil constriction, wide field of depth, +0.25, +0.5, +0.75 will all do perfectly fine.
Please add or detract from my understanding.
Darker lighting, more plus diopter?
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Rob,
You shoot with NO diopter under bright/ dark, all lighting condition?
You must have a vision of a 10 year old, able to zoom in , zoom out at will?
You said "proper prescription" made, do you mean "proper lens with +0.75 diopter" made? I can't imagine you can shoot under all lighting condition with just the distance vision.
You shoot with NO diopter under bright/ dark, all lighting condition?
You must have a vision of a 10 year old, able to zoom in , zoom out at will?
You said "proper prescription" made, do you mean "proper lens with +0.75 diopter" made? I can't imagine you can shoot under all lighting condition with just the distance vision.
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bpscCheney
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If you have the correct diopter, it will remain the same under all lighting conditions; it is focused on the front sight. That is its purpose.
To the surprise of many, the purpose of a diaphragm on shooting glasses is to maintain a uniform "pupil" size, not to manipulate depth of focus, though it can have that effect. (Or at least that's what Don Nygord told me when I bought my glasses from him.)
At that time, I bought three different diopters to play with. Now I use a single prescription lens to correct astigmatism and to focus on the front sight (with a diaphragm).
To the surprise of many, the purpose of a diaphragm on shooting glasses is to maintain a uniform "pupil" size, not to manipulate depth of focus, though it can have that effect. (Or at least that's what Don Nygord told me when I bought my glasses from him.)
At that time, I bought three different diopters to play with. Now I use a single prescription lens to correct astigmatism and to focus on the front sight (with a diaphragm).
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ShootingSight
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- Location: Cincinnati, OH
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There is an ideal place to focus, such that your depth of field is centralized between the target and the sight, which gives you the greatest benefit of whatever depth of field you have, large or small. In photography, this distance is known as the 'hyperfocal' distance.
If your focus shifts closer, the front sight will improve, but the loss of focus on the target is greater than the improvement on the front sight. If you shift your focus further out, you lose more on the sight than you gain on the target.
For pistol, the correct diopter to put your eye's relaxed focus at this hyperfocal distance is typically +0.75 diopters over your distance prescription.
This focal distance, and the associated diopter, is constant for all light conditions and depths of field. As your pupil constricts or dilates the total depth of field will increase, but the optical 'midpoint' in order to best distribute the depth of field between the sight and the target remains unchanged.
This optical math is valid for all shooters, of any age. The difference is that when you are young, you can use your eye muscle to pull your focal point in, whereas older people cannot, so they have to resort to a lens.
If you want the math, for the simplified case where the target is at optical infinity (which is true for any target over about 25 feet away), the hyperfocal distance is 2x the distance from your eye to the sights. I've done experimenting and taken measurements with pistol shooters, and the math works best when you base it on the distance from your eye to the rear sight. This will produce a very slight bias of sharper focus on the front sight.
Example, in my case, the distance from my eye to the rear sight is about 25", so my hyperfocal distance is 50".
Lens diopters are simply the focal length of the lens inverted (in meters). So a 2 diopter lens will focus at 1/2 meters, a 3 diopter will focus at 1/3 meters, and a 0.5 diopter = 1/2, will focus at 2 meters.
So, to focus at 50", which is 1.27 meters, I would want a 1/1.27, or +0.79 diopter lens. Lenses are available typically in 1/4 steps, and you always want to round down, so the 0.79 rounds down to a +0.75 diopter lens.
If your focus shifts closer, the front sight will improve, but the loss of focus on the target is greater than the improvement on the front sight. If you shift your focus further out, you lose more on the sight than you gain on the target.
For pistol, the correct diopter to put your eye's relaxed focus at this hyperfocal distance is typically +0.75 diopters over your distance prescription.
This focal distance, and the associated diopter, is constant for all light conditions and depths of field. As your pupil constricts or dilates the total depth of field will increase, but the optical 'midpoint' in order to best distribute the depth of field between the sight and the target remains unchanged.
This optical math is valid for all shooters, of any age. The difference is that when you are young, you can use your eye muscle to pull your focal point in, whereas older people cannot, so they have to resort to a lens.
If you want the math, for the simplified case where the target is at optical infinity (which is true for any target over about 25 feet away), the hyperfocal distance is 2x the distance from your eye to the sights. I've done experimenting and taken measurements with pistol shooters, and the math works best when you base it on the distance from your eye to the rear sight. This will produce a very slight bias of sharper focus on the front sight.
Example, in my case, the distance from my eye to the rear sight is about 25", so my hyperfocal distance is 50".
Lens diopters are simply the focal length of the lens inverted (in meters). So a 2 diopter lens will focus at 1/2 meters, a 3 diopter will focus at 1/3 meters, and a 0.5 diopter = 1/2, will focus at 2 meters.
So, to focus at 50", which is 1.27 meters, I would want a 1/1.27, or +0.79 diopter lens. Lenses are available typically in 1/4 steps, and you always want to round down, so the 0.79 rounds down to a +0.75 diopter lens.
Interesting subject.
ShootingSight - I think I follow your advice - applicable to a normal barrel length pistol ??
But for a long barrel pistol or, in my case a prone rifle where the emphasis is on maximum clarity of foresight
a) how does your advice work and
b) how do you maximise rearsight/diaphragm clarity whilst retaining principal focus on foresight then target image
Hope I made this clear :-(
John
ShootingSight - I think I follow your advice - applicable to a normal barrel length pistol ??
But for a long barrel pistol or, in my case a prone rifle where the emphasis is on maximum clarity of foresight
a) how does your advice work and
b) how do you maximise rearsight/diaphragm clarity whilst retaining principal focus on foresight then target image
Hope I made this clear :-(
John
If you use the hyperfocal distance, you must be assuming the shooter has functional ciliary muscle function to bring the focus to front sight.
What happen when you no longer have the ability to bring your focus from hyperfocal distance (1.3 meter +0.75) to 95cm front sight at all? There are people who are old enough (70's) who have no accomodating ability at all. For them your assumed hyperfocal distance is beyond their front sight distance.
For them, they can shoot well with +0.75 lens if light is bright enough. If lighting is poor, they will need +1.0 diopter lens ( focus 1M/1 = 1meter). No?
What happen when you no longer have the ability to bring your focus from hyperfocal distance (1.3 meter +0.75) to 95cm front sight at all? There are people who are old enough (70's) who have no accomodating ability at all. For them your assumed hyperfocal distance is beyond their front sight distance.
For them, they can shoot well with +0.75 lens if light is bright enough. If lighting is poor, they will need +1.0 diopter lens ( focus 1M/1 = 1meter). No?
Confused
I'm a little confused, because you've posted the question in the pistol forum, then start talking about prone rifle. Simply put you should be focusing on the foresight, no matter what discipline we're discussing. It is therefore irrelevant what the light levels are as the lens prescription you have works independant of the light. In very bright light use a filter to cut the light levels and/or glare.
Rob.
Rob.
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ShootingSight
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GNR, You can repeat the math example I gave, measuring distance from your eye to your rear sight. As stated, I have tested this with pistol shooters, and I get general agreement that the clarity of the front sight and target are about optimal.
For a rifle, the principle also works, but in this case, just base the math off the front sight. Usually it works out to +0.50 for a rifle (AR and carbine are +0.75, just about all rifles are +0.50).
Seamaster. My premise is that you want the lens to get your focus to the desired spot with your ciliary muscle doing zero work. This leaves the muscle relaxed, so you do not get drifting focus as it fatigues. The hyperfocal calculation is based on the notion that if you focus at the hyperfocal distance, the front sight is sufficiently in your depth of field that you do not need to shift your focus in closer. The idea of hyperfocal is that by centralizing your depth of field, you can get the front sight in the near edge of the depth of field at the same time as the target is in the far edge of the depth of field, and you can see both in focus at the same time.
I think some of the confusion is that I appear to be departing from conventional wisdom. It is typically taught that you want to focus on the front sight. I disagree with this on a technicality. I agree that you want to concentrate of the front sight, but in the optical sense, your focus needs to be out in front of the front sight, otherwise you lose too much target.
Conceptually, if you focus ON the front sight, all of your depth of field which falls closer than your focal point is simply wasted. If you shift your focal point out in front of the front sight, the post can still be comfortably inside your depth of field, so you don't give up anything, but you pick up a lot of clarity on the target.
If you want to do a cheap experiment, your 95cm front sight is just about 1 meter, so that would be a +1.00 diopter added to your distance vision.
Look on Amazon, you can buy cheap reading glasses. Most drug stores sell them down to 1.25 diopters, but on-line you can get a pair of 1.0. Note, these are not safety rated for impact, so I do not recommend actually shooting with them, but if you try tham on, you will get a fantastic front sight, but find that your target is too fuzzy.
For a rifle, the principle also works, but in this case, just base the math off the front sight. Usually it works out to +0.50 for a rifle (AR and carbine are +0.75, just about all rifles are +0.50).
Seamaster. My premise is that you want the lens to get your focus to the desired spot with your ciliary muscle doing zero work. This leaves the muscle relaxed, so you do not get drifting focus as it fatigues. The hyperfocal calculation is based on the notion that if you focus at the hyperfocal distance, the front sight is sufficiently in your depth of field that you do not need to shift your focus in closer. The idea of hyperfocal is that by centralizing your depth of field, you can get the front sight in the near edge of the depth of field at the same time as the target is in the far edge of the depth of field, and you can see both in focus at the same time.
I think some of the confusion is that I appear to be departing from conventional wisdom. It is typically taught that you want to focus on the front sight. I disagree with this on a technicality. I agree that you want to concentrate of the front sight, but in the optical sense, your focus needs to be out in front of the front sight, otherwise you lose too much target.
Conceptually, if you focus ON the front sight, all of your depth of field which falls closer than your focal point is simply wasted. If you shift your focal point out in front of the front sight, the post can still be comfortably inside your depth of field, so you don't give up anything, but you pick up a lot of clarity on the target.
If you want to do a cheap experiment, your 95cm front sight is just about 1 meter, so that would be a +1.00 diopter added to your distance vision.
Look on Amazon, you can buy cheap reading glasses. Most drug stores sell them down to 1.25 diopters, but on-line you can get a pair of 1.0. Note, these are not safety rated for impact, so I do not recommend actually shooting with them, but if you try tham on, you will get a fantastic front sight, but find that your target is too fuzzy.
And I disagree slightly. I don't think you do lose too much target but it has to be something that each person evaluates for themselves. So focus on the foresight and get a lens for that prescription. Then see if it works for you in the real world and you can see the foresight and that the target is not too blurry. There is no textbook setup that will work for all shooters and what all shooters find acceptable in terms of when blurriness becomes too much.ShootingSight wrote:I think some of the confusion is that I appear to be departing from conventional wisdom. It is typically taught that you want to focus on the front sight. I disagree with this on a technicality. I agree that you want to concentrate of the front sight, but in the optical sense, your focus needs to be out in front of the front sight, otherwise you lose too much target..
Rob.