TargetTalk

read the " Hitchhikers" on shooting glasses but did not see any mention of cataract surgery/multi-focal replacement lens after surgery. Is there anything written on the effect of focus on the front sight in 10 meter AP if a person has multi focal implant lens after cataract surgery. I had cataract surgery with multifocal lens implants and seem to be able to clearly see the target , front sight and rear sight all clearly at the same time no matter that I am trying to focus on the front sight only. The concentric rings in the lens seems to turn the job of focus into something that is involuntary.
Any thoughts or am I just a crazy 70 year old?

I am looking to buy shooting glasses but am unsure if that will allow focus on the front sight while slightly blurring the rear sight and target?
If you are aware of anything that has been written on this I would love to look it up and research

You need a good optometrist to test your eye(s), make any corrections, and add enough magnification to pull the focus to the front sight. You can have all this in one lens for a specialized shooting glass setup.

OR You can go to the 99 cent store and buy two or three pairs of reading glasses (+0.25 to +0.75 for a start) and play with it yourself. Put a strip of matte cellophane tape on the glass of the non-shooting eye.

OR you may be a barmy old fart like myself.

Risking life, limb and reputation by contradicting ol' Rover, but I'll take the chance. DON'T go to the dollar store and try out reading glasses. Cataract patients have special requirements.

Ask your eye doc if you can bring your AP into his office (cased of course). Once he gives you approval, tell him exactly what you're looking for - sharp focus at front sight and inability to focus at 10M. He'll do the rest as long as you've made it clear what you want. If he won't let you bring your pistol, which I think unlikely, ask him to refer you to an optometrist with no such objections.

Good luck & give us a progress report.

I may have to risk reputation, although not life or limb, to stand with Rover on this. I had cataract surgery, both eyes, some years ago. I don't think that there are any special needs involved.

Your ophthalmologist probably replaced the natural lens with a plastic one that gives you clear distance focus. This allows you to see anything from about 20 feet out to infinity in focus. In optical terms, you have a depth of field from 20' to infinity. Reading glasses bring the zone of sharpness much closer but the depth of field becomes much smaller. If you get a lens that brings the front sight into sharp focus, there is no way the rear sight or the target will also be in focus.

From my own experience, the narrow depth of field adds a couple of considerations that others shooters don't have to deal with. Since standard lenses only come in .25 diopter steps. the precise prescription that you need may not be readily available. There are a couple of ways around this. If the shooting glasses have an adjustable bridge, it can be used to change the distance between the lens and the eye and this changes the effective strength of the lens. Also, the distance from your eye to the front sight is shorter for a face-on stance than for an oblique stance so that can be adjusted a bit for clarity. Changing between guns with different sight radii can also be an issue - I usually shoot a TOZ 35M, Morini AP and S&W Model 52. The first two have a much longer sight radius than the Smith and I have to adjust the bridge on my Knoblochs to switch between them.

But if you are just shooting one gun, drug store readers might fill the bill and are cheap enough to be worth a try. I might go with something stronger than Rover suggested, maybe +1.0 to +1.5. It might be a bit tricky finding a drug store where no one will freak when you whip out an AP ...

Roger

You are not crazy ... well, maybe you are, but not on this subject.

Seeing the sight clearly and blurring the target is an old wives tale. It is based on shooting with the naked eye, where the depth of field is relatively poor, so you need to choose to look at either the sight or the target, but not both. Looking at the sight is the better option of those two lousy choices.

However once you start adding a lens and/or a small aperture, the game changes, and you can see both clearly at the same time.

Your cateract surgery put in multifocal lenses which use the same technology as the microsight. If it allows you to see both at the same time, dont fight it.

Now, if you want to go stronger front sight, I sell safety glasses with +0.50 lenses built in, so that would do it.

Art Neergaard
ShootingSight LLC
www.shootingsight.com
513-702-4879

william wrote: Ask your eye doc if you can bring your AP into his office (cased of course

Last month I finally received my back-ordered Olympic Champion frame with lens holder and iris, so I went to an eye doctor to have a thorough check-up (first ever, at 50 years old) and to be measured for a shooting lens. I'd read in a search online that the particular office (Pacific Eye Doctors in Richmond, BC) had an excellent reputation for dealing with shooters in various disciplines. The exam took me through a bunch of sophisticated machinery and loads of lens tests and questions before settling on a general prescription (got variable-focus 'office' glasses, finally getting away from awful drugstore glasses) and on a couple of lenses for my shooting frame. I asked for both a 10metre focused and a front sight focused lens, in hardened but un-coated glass, as I've pretty well settled into focus on the target, centre-aim, but wanted the option to check on front sight focus in case it ever feels more comfortable for me. Checked for a couple of days... nah, it was awful and I happily returned to target focus.

I found out a few good things about my general health and eye health and really felt it was a worth-while thing I shouldn't have put off so long. The multi-layer retinal imaging stuff was fascinating, and it was good to learn that my blood pressure is normal, retinas healthy, no trace of glaucoma etc, and that my vision is 20/15 making me especially good at seeing things far away - something I knew already but nice to have it confirmed. I highly recommend a visit to a reputable eye doctor. A very positive experience. And I'm thrilled with my shooting lens, makes a significant difference compared to the somewhat wobbly quality of the previous dollar store lens I'd cut round for my previous Varga glasses.

But the main reason for my posting here was something the doctor told me about a previous shooting customer. He was very clear on the phone about keeping the pistol in a proper case when bringing it in, and about shutting his office door (there were several doctors sharing the office along with various receptionists and optometrists, and lots of clients) before I got out the pistol. This one fellow was a rifle competitor, a few years back, and they'd had the rifle out by the front window pointing it across the street at a parking sign to find the right lens... A bit of an error in judgment it turned out, as the police were called and arrived quite soon afterwards, though after the rifle had been put away. So no guns-drawn stuff, just a few uncomfortable minutes of questions. So yeah, be very sure the procedure is spelled out clearly with your doctor before the visit.

There are far better shooters than I on this forum who can comment on the "old wives tale" of not being able to hold the sight and target in focus at the same time, but I'll toss my tuppence in for what their worth.

There are two definitions of "focus" involved here. One is the visual definition of sharpness of image. The other is the focus of attention.

When you are shooting your attention must be focused on maintaining ideal sight alignment. If your attention is shifted to the target, then the sight alignment will quickly drift away from ideal. When the sight alignment is ideal, then the gun is always pointed directly at the plane of the target and the area in which the shot will land is determined by the the movement of the gun away from the aim point. This movement and the corresponding error is surprisingly small and improves with practice. If the sight alignment deteriorates, i.e., the front sight drifts away from its level and centered position in the rear sight notch, then the barrel of the gun is no longer pointed directly at the target but at some angle to it. The angular deviation causes a much larger shift in the point of impact than the lateral deviation of perfectly aligned sights.

A bifocal designed to put the front sight in visual focus below the line and the target in visual focus above it will still not put the sight and target in visual focus simultaneously. Switching focus means the time it takes to get the shot off will be longer than necessary and this will not improve the steadiness of hold either. My guess is that you will likely hit a large number of small numbers and probably be unable to call your shots with any consistency.

As far as an aperture is concerned, I have one and found it unhelpful. Stopping down to a small aperture will greatly increase the depth of field and may even bring the front and rear sights and target in focus simultaneously. Stopping down also decreases the amount of light reaching the eye and having the target in visual focus increases the temptation to shift attention to the target. Neither effect helped my scores, but YMMV.

My experience is with slow fire only - I'm sure there are other considerations for other disciplines. However, if you are shooting 10M AP then a sub-six hold with visual and attentive focus on the front sight will probably give you the most satisfying results.


Roger

Sorry for the possibly too brief and provocative answer - I did not want to derail the thread, which was started asking about multi-focus cateract inserts. These use a diffractive focus technology which is well beyond the scope of ordinary diffractive lens discussions.

However, to avoid starting contraversy, let me clarify my comments.

Background. My name is Art Neergaard, owner of ShootingSight LLC, I am a Highpower shooter - Service Rifle mostly. I am a mechanical engineer, but also studied some optics. I am a technical photographer, which means I suck at the artistic part, but I understand lens settings. I am NOT an eye doctor. So while I understand the physics of lenses and imaging, I cannot comment on eye diseases beyond the basic near sighted/far sighted/presbiopic conditions. I founded a small company, and I make and sell corrective lenses for shooters.

Shooting is a game of depth of field. You are trying to juxtapose a nearby front sight and a distant target, so you want to see both clearly at the same time. THis is especially true if you are shooting a 6 o'clock hold. As a photographer, I know that if I want to take a picture of a person, and have the mountains behind them also be in focus, there are two things I want the camera lens to do: first is to focus at what is called the hyperfocal distance of my subject. THis will centralize my depth of field so the subject is at the near end, while the mountains are at the far end. THe second thing I want to do is to use as small an aperture as possible, to maximize that depth of field. Regrettably, small apertures cut out light, so the practical limitation is that you want to use as small an aperture as possible without dimming the image.

Lens power is what drives where the human eye will focus. Normally, the cilary muscle in your eye is relaxed, and your lens will be big and flat and you focus at infinity. As you exert the eye muscle, it squeezes your lens to be small and fat, and you focus up close. Either due to presbiopia, or just to avoid muscle fatigue in your eye, a better solution is to add an eyeglass lens which will shift your focus closer, so the eye muscle does not have to exert itself. We can actually apply photography formulas to determine what lens you want.

Hyperfocal distance, assuming the target is at optical infinity (and anything 50 ft and over is effectively at optical infinity) works out simply to be 2X the distance to the near object. So, if you have a 30 inch barrel, your hyperfocal distance is 60 inches. If your eye is focused at 60 inches, whatever depth of field you have will be balanced between the front sight and the target.

Now, what lens do you want? Lens focal length is simply the inverse of the diopter power. A +2 diopter lens will focus at 1/2 meters. A 3 diopter lens will focus at 1/3 meter, and so on. If I want to focus at 60 inches, which is 1.5 meters, I would want a 1/1.5 diopter lens, which is a 2/3 or 0.66 diopter lens.

Now, lenses typically come in steps of 0.25 diopters, and for anatomical reasons I won't go into, you always want to round down, so for your 30 inch barrel, you want a +0.5 diopter lens. If you have a much shorter sight radius, as in for pistol or an AR-15, the optimal lens typically works out to +0.75. If you shoot pistol and have very short arms (ie women) you might arrive at a +1.0. All of these numbers, if you wear glasses for distance, you would take this calculated number and mathematically add it to the spherical component of your glasses prescription.

So, in summary, there is an optimal focus setup to distribute your depth of field. In addition, using a small aperture will broaden that depth of field, so long as it is not so small that it dims it out.

If these two steps are done correctly, you will arrive at a point where the target and the front sight are in optical focus at the same time, and you will see as well as you did when you were 18.

Art Neergaard
ShootingSight
www.shootingsight.com
shootingsight@nuvox.net
+1-513-702-4879

In my first paragraph, I meant to type:

"These use a diffractive focus technology which is well beyond the scope of ordinary refractive lens discussions. "

I don't see an edit button anywhere.

Art

Upper right corner of your post.

Rover wrote:Upper right corner of your post.

Doesn't work if you're signed in as a guest.

OK, I have signed up as a member, from here on out I can correct brain farts.

AHA! And now I do have an edit button.

I guess since a guest goes in with no password, it is impossible to verify if the person who wants to edit is the same person who wrote the message.

Thanks for an informative thread. Now the hard part is finding an Optometrist who understands my needs.
Anyone in Atlanta recommend a good one who understands shooters needs?

Go to any old optometrist, and get your distance vision checked. Email me the prescription, and I will help you do the conversion for shooting, and I can even make some lenses to fit (I only do round lenses).

Art

At this stage I can vouch for the work done by Art. I have just fitted one of his lenses to my frames and from a casual test it all seems good. I'll be testing it on the range tomorrow night.
Art has been great to deal with from the other side of the world and was able to user the script I emailed.
He's getting two thumbs up from me for service.