Eyewear confusion

[richard66]

I'm confused by the use of devices such as the EyePal or an aperture mounted on eyeglass frames. My understanding is that a lager aperture on a camera or an eyeball results in LESS depth of field. So wouldn't limiting the light entering the eyeball by putting an aperture in front of it result is less depth of field, and an even fuzzier target when focusing on the front sight? There's something I'm not getting.

BTW, this isn't the low-hanging fruit when it comes to where I should be looking for improvements ...

[Gwhite]

A small aperture INCREASES depth of field. The extreme case is a pin-hole, where there will be very little light getting through, but everything is in focus. Once an aperture is larger than your pupil, it will have no effect on depth of field. The stick on apertures are small enough that they can increase depth of field significantly, but that can cause problems.

The most important thing in pistol shooting as far as the vision side of things is concerned is maintaining sight alignment. Many shooters find that using a small aperture that makes the target sharper is detrimental to good shooting because it makes it too tempting to focus on the target and their sight alignment suffers. An aperture can help adjust for varying light levels, and it can help to get both the front & rear sights in focus. In general, it should NOT be used to make the target image sharp. In additional to making it easier to ignore the front sight & sight alignment, making it that small can also cause eye strain because you are losing too much light.

I use a combination of a moderate corrective lens (+1.0 to +1.25 diopter) and an aperture, but I don't crank it down very small.

[richard66]

Thanks, that clears it up for me. I was thinking of the effect that the aperture in front of the eye would have on the aperture in the eye, or the iris. I figured -- pinhole in front of the eye equals large opening of the iris equals small depth of field. I guess it is the aperture in front of the eye alone that is determining depth of field.

I tend to wear nonprescription +2 reading glasses much of the day: I'd say they improve my view of anything out to a couple of yards. I wear them for shooting because the front sight wouldn't be sharp without, but it has been suggested in another forum thread that the readers one uses in daily activities are too strong for shooting. Should I visit the reading glasses display in my local drug store and try everything from .25, working my way up until I find the lowest power that brings the front sight into focus? Note: I won't actually take my pistol into the drug store ... I'll find a stand-in.

Actually, I think bricks-and-mortal reader selections tend to start around 1.25.

[Rover]

Two things: Yes, you can change depth of field by varying the aperture. Don Nygord told me when I bought my shooting glasses from him, that the REAL purpose of the aperture was to maintain a UNIFORM "pupil" size, therefore avoiding changes caused by defects in the eye.

Don't bother with the "99 cent store" glasses. Get the real thing, correcting things like astigmatism. Don't even THINK about vari-focals.

[ihasagun]

I use an iris cranked as small as possible because it corrects my astigmatism. But at the match I attended to observe. I did not see anyone using an iris. My guess is that they either had lasik and were just using a diopter lens, or else had an astigmatism prescription in the lens along with the diopter. I plan to get lasik at some point.

[Gwhite]

Thanks, that clears it up for me. I was thinking of the effect that the aperture in front of the eye would have on the aperture in the eye, or the iris. I figured -- pinhole in front of the eye equals large opening of the iris equals small depth of field. I guess it is the aperture in front of the eye alone that is determining depth of field.

I tend to wear nonprescription +2 reading glasses much of the day: I'd say they improve my view of anything out to a couple of yards. I wear them for shooting because the front sight wouldn't be sharp without, but it has been suggested in another forum thread that the readers one uses in daily activities are too strong for shooting. Should I visit the reading glasses display in my local drug store and try everything from .25, working my way up until I find the lowest power that brings the front sight into focus? Note: I won't actually take my pistol into the drug store ... I'll find a stand-in.

Actually, I think bricks-and-mortal reader selections tend to start around 1.25.

That's true. Some "computer glasses" come in lower power. The general recommendation for shooting is to start at +0.75 diopter. They also make safety glasses with the appropriate correction. This is what I would recommend:

https://www.safetyglassesusa.com/elvex- ... magnifier/

For the price, you could get +0.5D, +0.75D and +1.0D and experiment.

[cuslog]

My daily prescription reading glasses are ~2.75. At this strength, the focal length is only about 16", fine for reading the paper or computer work but too "short" for pistol shooting. For that, I use the Elvex +1.5 safety glasses -- the focal length at this strength gives me a nice sharp focus on the front sight. The bonus is that these are "ballistic rated" safety glasses.

[David M]

The general recommendation for shooting is to start at +0.75 diopter. They also make safety glasses with the appropriate correction.

To expand this a bit, use +0.5 to +0.75 diopter de-focus increase on top of your normal distance script.
Get your eyes checked to find out your script (every 2-3 years).

[ShootingSight]

The relaxed human eye will focus at infinity. Also, if you have distance correction glasses, the corrected eye will focus at infinity.

Adding positive diopters, either as a separate lens, or by adding the power to your prescription, will bring your focal point closer, and the formula is that diopter is the inverse of focal length - in meters. So adding a +2.00 diopter lens will make you focus at 1/2 meter. +3.00 will focus at 1/3 meter. Inverse works: adding 1/2 diopter will focus you at 2 meters.

For shooting rifle, you want to see your front sight and the target together, so you calculate the diopter to see the front sight perfectly, and the diopter to see the target perfectly (this usually rounds to zero for anything over 10 meters), and you average the two. So for a rifle with a 1 meter sight radius, and a 100 meter target, you would calculate a 1 diopter to see the sight, and a 0.01 diopter to see the target, so you would shoot with a +0.505 diopter (rounds to +0.50).

For pistol, run the math based off your rear sight and it comes to +0.75 diopters for most people to balance your focus. THis is a good starting point, however in pistol, sight alignment is more important than sight/target alignment, so many people prefer to use slightly more power, to bias their focus towards the sights, so maybe a +1.00.

On top of lens power, which determines where the center point of your depth of field falls, aperture size determines how big your depth of field is. A smaller aperture makes a bigger depth of field, but lets in less light, so it is not a free lunch. If you use no aperture, it is your pupil that determines depth of field. If you use a peep sight, the peep determines. In outdoor shooting, there is enough light that you definitely get a benefit from a reduced aperture, in indoor shooting, it depends on how good the lighting is. Your minimum pupil size is about 1/8". For my eyes, I can usually get away with a 0.070 or even 1/16" aperture indoors. Outdoors I can go as low as 0.040 (1mm).

EyePal is an expensive solution so you can stick a static plastic patch on. Get a piece of black electrical tape and punch a hole in it. You can buy steel hypodermic tubing from McMaster for a few dollars for a 12" piece. Roll it on a belt sander to chamfer the end, and it makes a great little core drill to cut clean holes of whatever the ID of the tubing is.

[218bee]

My reading glasses are 1.50 strength. I simply cut the power in half, to .75 and it made a world of difference. Front sight is much clearer than before. These safety-rated glasses are cheap, and a 3-pack can be had for $24 shipped.

[Azmodan]

hi
i read some of the threads on optics, but i am still confused. maybe because i don;t know much about glasses or maybe here we have different terminology:
for my understanding, there are 2 types of lenses: for close distance (reading) and far distance (normal wear)
for reading glasses, the diopters are marked with + sign and the distance glasses, the diopters are marked with - sign

i've read that for shooting clarity one would need a +0.75 diopter added to the distance prescription.
i have a -0.50 prescription (distance glasses) and nothing for close (no reading glasses).

so my question is, how should my prescription be changed for shooting?
* +0.25 (mathematical adding)
* -1.25 (adding 0.75 to my 0.50 distance prescription)
* +0.75 (ignore distance prescription, use reading diopter only)
* other value?

[David Levene]

For pistol shooting the starting point would be a lens strength of +.25. Do you know whether your have any correction for astigmatism?

[Azmodan]

no idea... this is the result of the eye exam...

so a +0.25 : that's almost like the naked eye. the thing is, with the -0.50 diopter, the front sight is more clear than with the naked eye, so the glasses do work...

[David Levene]

From my reading of that prescription you have a distance prescription of +0.25. If you add +0.75 you will get +1.00.

Assuming that you are right eyed you need a -1.25 astigmatism correction at 88 degrees.

But hey, I'm not an optician.

[Gwhite]

The "cylinder" numbers indicate that you have significant astigmatism. A plain +0.25D lens is going to produce some distortion. You need to add +0.75D to the "SPH" numbers, and get a lens ground to include the astigmatism correction. At least I think that is right...

Art Neergaard at: http://www.shootingsight.com/ is an expert at this stuff. He recently fixed up most of the team I help coach with shooting glasses.

[Azmodan]

the doctor prescribed a -0.25 (left) and -0.50(right) glasses. the sight improved for both eyes, but i still aim with my left eye (i am right handed) because the right eye image is still too blurry (the glasses were done for work/computer, not shooting)

guess i have to go back to the doctor for another prescription for shooting glasses. but i;m afraid she will not know anything about shooting - i don;t think there is a person that knows anything about 10m pistol shooting in a 200 km radius, optics or anything else :) - so i'd like to know as much as possible myself before, so i can get a good prescription

[Rover]

It's simple: First, get your astigmatism corrected, then have your eye(s) focus on the front sight, whatever correction that is. Bring your AP with you for fitting. Cover the back of the lens of your non-shooting eye with matte cellophane tape.

[Azmodan]

It's simple: First, get your astigmatism corrected, then have your eye(s) focus on the front sight, whatever correction that is. Bring your AP with you for fitting. Cover the back of the lens of your non-shooting eye with matte cellophane tape.

that is exactly what i intend to do (and i'm sure the doctor will freak out when she'll see the gun) but i want to understand the whole "add 0.75 to your prescription" business

[-TT-]

You don't really need to bring in the gun, the important thing is the distance from your shooting eye to the spot you want it to focus on, when you're in your normal stance. It's farther than reading or computer use, but she'll figure it out if you pose with a pencil or something in your hand. Ok, maybe bring a tape measure. :-)

[Gwhite]

Having a prescription that pulls your distance (relaxed) focus all the way in to the front sight may make the target blurrier than you would like. The diopter strength is 1/f, where "f" is the focal length in meters. The recommended starting point of 0.75D has a focal length of 1.33 meters, which is well past your front sight. The team I help coach has many students that prefer only +0.5D (2 meter focal length) added correction because the target is less blurry that way. A lot will also depend on the typical range lighting where you shoot. Bright lighting will help to increase your depth of field, and make the target less blurry.

Another approach is to experiment at the range with something like this:

https://shootingsight.com/product/test-lens-frame/

along with your regular glasses to see how much correction you like.

Depending on what sort of glasses frame you are using, you may want to start out with +0.5D added to your prescription, and then try clip-on lenses to test additional correction. I've done that with my Champion Brillen frames.