TargetTalk

I'm 71 years old. When I order shooting glasses, should I add the same magnification that I use for reading ?
OR
Just the recommended +.50 ?
Thanks for a reply !

I suppose the rear sight is further away than reading distance? +1 and a diopter might work.

Kent (73)

Have your eyes checked and what ever your distance script is,
add +0.5 to +0.75 to that script.
As you get older your eyes may not adjuct as well you may find you need a little more.
It may take some trial and error testing to get it right.

Put on your reading glasses, and read this:

http://www.nxtbook.com/nxtbooks/nra/ssu ... ex.php#/16

Basically, it's complicated...

I did it the easy way, I went to the dollar store. I dont wear glasses yet, so I bought a 1.0, 1.25 and 1.5.... 3 dollar experiment and then I knew what Knoblock lenses to use......

Are my powers of logic slipping or are those people suggesting making a positive addition to their reading prescription just plain wrong.

The generally accepted norm is to make a positive addition to your distance prescription to bring your focus back on to the front sight.

Surely if you want to move your focus forward from a reading distance to the front sight you would need to make a negative addition to your reading prescription: I'm guessing at about -.25

I would still rather work on the normal (well tested) method of your distance prescription with a +.75 addition.

Increasing the diopter strength moves the focal point closer to the eye.

deadeyedick wrote:Increasing the diopter strength moves the focal point closer to the eye.

That's why I cannot understand people suggesting an increase on a reading prescription.

m1963 wrote:David- you are right, +.5 to the diopter, diopter, not reading, prescriptions.
m1963

I think you are using the word "diopter" when you mean "distance".

Diopter is simply a unit of measurement of the strength of a lens.

Im not suggesting a increase to a reading prescrption. I'm suggesting using inexpensive reading glasses to find the strength of the lens necessary to replace your glasses or improve your sight clarity at the fixed distance we hold a pistol... Being a diabetic, mine moves bit with blood sugar....

Hello- unfortunately, I have worn glasses all of my life. Diopter means something to me because of this. It may not mean something to others, though.

Here is how I understand it: a diopter is used to identify the light bending capacity of a particular lens. A higher diopter means there is a higher light bending capacity, and thus a greater magnification.

Kind regards,
m1963

m1963 wrote:Hello- unfortunately, I have worn glasses all of my life. Diopter means something to me because of this. It may not mean something to others, though.

Here is how I understand it: a diopter is used to identify the light bending capacity of a particular lens. A higher diopter means there is a higher light bending capacity, and thus a greater magnification.

Kind regards,
m1963

That's pretty much right, with the table referring to positive diopter strengths, but I am still confused by your second use of the word diopter in the post I quoted.

Many people will have negative diopter prescriptions for distance (normal) use.

IF you need a lens only for reading it is a + lens. Can you read text at the distance where the front sight is? If so a + lens of 0,5 might work. I used the word diopter wrong, it did not translate well to English :-) I meant a devise to make more or less opening.

From this months Shooting Sports USA

http://www.nxtbook.com/nxtbooks/nra/ssu ... ex.php#/24

I simply took my pistol to the optometrist, held the pistol as if aiming and chose the lens that showed the front sight most clearly... Why complicate a simple solution.

For those who wouldn’t/couldn’t take their pistol to an optometrist...make up a wooden jig with a nail where the sight is and go to the $2 shop and find the correct diopter lens yourself.

Total cost....$2 !

It’s not hard to pick the correct lens....it’s usually the one where the foresight is clearest.

A lens to show the most clear front sight is the wrong answer. The correct answer for pistols with iron sights is typically +0.75 added to your distance prescription. This lens will achieve the hyperfocal distance of your rear sight, centralizing your eye's depth of field between the rear sight and the target, so you can see the rear sight and target with equal clarity, and the front sight is slightly sharper than either the rear or the target.

Diopters are the inverse of a lens focal length, in meters. ie a +2.00 diopter lens will shift your focus from infinity to 1/2 meter. A 3.00 diopter lens will focus you at 1/3 meter. It also works with fractions: a 1/2 diopter lens will focus you at 2 meters.

Inverse focal length is not a rational concept, but is rather a mathematical manipulation of the lensmaker's equation, used to calculate focal points in a lens. The actual formula is not germane to this discussion, but suffice it to say that doing lens math in diopters is much easier, allowing straight addition and linearizing error.

Your eye has a natural depth of field which extends both closer than and further away than your eye's focal point. In order to get the best sight picture, your eye/brain will naturally focus on a point BETWEEN the sight and the target, such that your depth of field is centered between the sight and the target. This way, the sight falls just in the near edge of your depth of field, at the same time as the target falls just int he far edge of your depth of field, and your eye can see both together at the same time. The focal point that distributes your depth of field between a nearby object and optical infinity is referred to in phtography as your hyperfocal distance.

One of the nice thing about diopters linearizing error, is that hyperfocal calculations are easy to do through straight averaging. For me, the rear sight on my pistol is about 24" from my eye. So to see the rear sight perfectly, I would convert 24" to meters (0.61 meters), and then invert that number (1/1.61 = 1.6 diopters). So adding a 1.6 diopter lens to my distance vision prescription (or just using a 1.6 diopter lens by itself if I have perfect distance vision) will give me a perfect rear sight focus. Next, target focus. If my target is at 10 meters, the lens I need to perfectly focus on my target is 1/10 diopters, or 0.1 diopters. Note that since the smallest step a human eye can typically see is 0.125 diopters, the 0.1 could be rounded to zero with little impact on the outcome, but for the purposes of the math here, let's keep it.

If I need a 1.6 diopter to see the rear sight, and a 0.1 diopter to see the target, the lens I need to focus at the hyperfocal distance is exactly half way between the two, or 1.7/2, or 0.85 diopters.

So if I add a 0.85 diopter lens to my distance vision, my depth of field will be centered between the rear sight and the target, so both will be equally clear. The front sight being more solidly inside the depth of field will be slightly more clear than either.

The human eye can exert the ciliary muscle to add diopters internally, so you can focus up close, but there is no opposing muscle to subtract diopters from your eye, once it is fully relaxed. So if the math says you need 0.85 diopters, and lenses only come in 1/4 diopter steps, you want to round DOWN to +0.75 diopters, and your eye will add the extra 0.1 diopters.

You can test this: 1.5 diopters is a standard power of reading glasses that you can buy for $5 at a drug store. Get a pair and try them, or if you have a distance prescription, try them on top of your glasses or contacts, so you are looking through both lenses at the same time .... what you will see is a FANTASTIC rear sight, but your target will be so blurry that it is not useful.

So in conclusion, the answer is to add +0.75 (you can repeat my math above using your own arm length as a basis, but you will likely end up at the same value). This is a derived answer, not a trial/error answer, so in my experience it works for 95% of the people out of the gate without needing anything more than a current distance prescription. Obviously, there are some with long/short arms, or whose eyes are a little out of tune with their prescription, etc so sometimes people end up 1 step above or 1 step below this solution, but in the vast majority of cases - it works.

A few years ago I visited my eye doctor at kaiser, and obtained a perscription for computer distance, which also turned out to be perfect for pistol shooting at arms length. Rather than getting bifocals or trifocals, I purchsed a pair of single vision glasses from Zinnei optical on line for about $20.00.

When shooting my air pistol, at 10 meters both the front & rear sights are razor sharp, and the target is a little fuzzy. This is to be expected, because the eye cannot focus on both close and distance at the same time. You may not be aware of it, but the muscles in the eyes are always flexing your eyes back and forth trying to accommodate the difference in the distance.

In my case I am 80 years old and this has worked well for me.

The same is true in shooting high power rifle matches. Focus on the front sight, and don't worry about the target being a little blurry.

I hope this helps to make it simple.

I have tried the hyperfocal lens thing and it did not work for me at all, a lens which focuses on the front sight is what I needed.

I suspect the hyperfocal lens idea has come from shotgun shooting, where there is no rearsight and its as important to see the foresight as the target.
In pistol shooting its much more important to see the sights as well as possible and the (static) target is much less relevant.

JamesHH wrote:I suspect the hyperfocal lens idea has come from shotgun shooting, where there is no rearsight and its as important to see the foresight as the target.
In pistol shooting its much more important to see the sights as well as possible and the (static) target is much less relevant.

It's the norm for rifle shooting with static targets. However, our aim us steadier, so having a clearer target is no disadvantage.

Here is an even better solution. The Merit iris. They have a tiny suction cup, and can be placed anywhere on your glasses. By adjusting the iris, you can bring the front and rear sight along with the target into sharp vision.

They sell for about $50.00, and as it is not mounted to the pistol, I think it is competition legal.

It works exactly like the rear aperture sight on a rifle, or the lens in a camera. As you close it down, you increase the depth of field.

https://postimg.cc/gallery/1yb7nuxq2/