Service Rifle Front Post Refraction

[FrankNatoli]

Am 61 year old hipower M-14 service rifle competitor having progressively increasing vision problems. When looking through rear aperture, front post aligned, but not yet with sight picture, aiming black well above front post, I can see everything reasonably well, including the aiming black. But as I move into sight picture, as the front post nears the aiming black, the aiming black begins to gray or white out. First saw this problem only at 600 yards prone slow, but over the years the problem has moved closer, and at a match this past weekend saw the problem at 200 yards. My guess is that light rays coming from the target white are being refracted by the front post, and my eyes are seeing target white rays where the aiming black really is. The problem isn't 100% consistent. Two weeks earlier, at a full 600 yard range, with a light and dark day, I had reasonably good vision for prone slow. But last weekend, at a 300 yard range, intense clear sky, I had terrible vision for prone slow. Same rifle. Same carbide lamp blacking. Same efforts to oxygenate and minimize time looking through the sights. I'm guessing a possible solution is to replace the standard width front post with a custom made front blade,the theory being the narrower the front sight, the less the refraction. Any suggestions?

 

[taliv]

hey welcome to THR

interesting question. I've never even considered how light might refract off the post. given that "black" absorbs the rays from all wavelengths and is really the absence of light, i am at a loss to explain how refraction is possible there.

i wonder if it's possible that there's some little bit of mirage right on top of the post due to the sun heating it different. i wonder what would happen if you carbide blacked the FRONT of the post and then put a white mark of some sort on TOP of the post. maybe use a paint pen or something

(I don't actually think that makes sense... as it would be the same for everyone and not depend on aging eyes for an explanation)

 

[FrankNatoli]

Taliv: thanks for your reply. I haven't had a physics class in many, many decades, but absorption and refraction are very different things. The latter has to do with bending light, and my theory is that is what is happening, and the front post is the culprit, though somebody expert on optics and refraction would have the last word on this subject. I'll try your suggestion of marking the top of the post. I've already heard of marking the rear of the post, facing the shooter, to give the shooter something fine to focus upon [haven't done that]. I intend to take an 03 to the range and use its front blade sight and rear ladder aperture sight to test my theory. If I get graying out with the M-14 and not with the 03, I have my answer.

 

[MistWolf]

Frank, the problem is due to your eye problems. your having glare in your eyes. I'm starting to have the same problem

 

[rcmodel]

Might be time for this:
http://www.meritcorporation.com/index-2.html

rc

 

[FrankNatoli]

rcmodel: thanks. I have something similar from my days in Conventional Pistol competition. It's an adjustable iris that clips onto your eyeglass lens. I'll give it a try.

 

[hps1]

Consider yourself lucky that your eyes held up as long as they have. Many of us experienced this problem earlier in life.

The first manifestation, as you have discovered, is the inability to get a clear 6 o'clock sight picture, which results in a vertical stringing group. As you mentioned, scores improve on overcast days, or at least they did for me.

In 1983, or thereabouts, lenses (other than corrective shooting glasses) were prohibited in NRA "iron sight only" matches. The rules committee finally allowed the use of one lens in either the front or rear sight in the match rifle category. Today, you can extend your ability to shoot "irons" by adding a corrective lens to your rear sight, or you can wear corrective shooting glasses.

I believe that CMP has also made rule changes that allow this in service rifle competitions as well. There is an outfit that makes a set of lenses that fit in the rear sight hood on M1/M1a.....not sure what is available for the AR platform.

After much experimenting, I found that a +.5 lens did wonders in sharpening up the front sight on most days, and had a set of three lenses ground to fit in the rear sight of my bolt gun (+ .25, +.50 and +.75). Too much strength and your target blurs excessively, too little and front sight is a bit fuzzy. Light changes govern correct power.

You can determine your own strength by trying out a few of the "over the counter" reading glasses, but some of them are not the best lenses out there, so best to find an optometrist that will work with you. Mine let me bring my rifle, and a reduced target and he would insert lens blanks between my eye and rear sight allowing me to pick the strength that did most good. Be aware, however, that since the target is much closer, the lens that looks best in the office, will likely be too strong on the range.

One humorous incident occurred when the lens fell out of my rear sight in the middle of a sitting rapid fire string. Took a couple of rounds to realize what had happened; needless to say, score suffered considerably.

Regards,
hps

 

[Howard Roark]

Bob Jones has lenses for M1As and AR15s. He is very good with his customer service and a call to him would be very worth while.

Another option is a multifocal lense. These lenses allow the eye to focus on two planes at once, front sight and the target. Creedmoor Sports has a MISO M1A Lens Kit that could be a better fix for you than the lens from Bob Jones.

Stallings Machine created the origional MicroSight for the AR15 rifles.

 

[FrankNatoli]

Howard: thanks. I'll drop a line to Bob Jones and see what they say.

 

[hps1]

WOW!

Howard, have you used the MISO lens? If it works as advertised, it would surely be the answer to aging eyes! Sure wish something like that had been available 20 years ago; wouldn't have had to give up service rifle competition and switch to bolt gun.

Not sure I understand how one lens can focus at multiple distances, especially front sight, target and "all distances in between" or something like that??

By the way, here's a link to Creedmore's listing:

http://www.creedmoorsports.com/shop/Miso-M1A-Lens-Kit.html

Regards,
hps

 

[Edarnold]

My suggestion, based on my own hi-power competition experience, is to stop blaming your sights, and get thee to an ophthalmologist. Your problem sounds like either a cataract, which will gradually over the years make objects close together blend together (like highway street signs at night) or deterioration of the high resolution portion of the retina. I thought I could see the sights on my M1A just fine, but kept getting cross-fired rounds on neighboring targets. Seems like that cataract allowed me to keep a useable sight picture, but I couldn't resolve the target frame numbers. Better to deal with eye problems earlier than later.

 

[Howard Roark]

hps1,

I have a MicroSight on my service rifle. Here is a link to an article at Accurate Shooter about the zone plate lenses:
http://bulletin.accurateshooter.com/2010/05/breakthrough-microsight-technology-improves-iron-sights/

I'm not sure what kind of lense that MISO is using that allows the range of movement that a M1A sight needs.

I do know that the MicroSight has to be perfectly aligned in order to work correctly. The problem with a LOT of AR15 sight leafs is that they are not perfectly square to the front sight. The manufacturer of the MicroSight makes an alignment tool and has a laser that he can screw into the sight leaf and align it to the front sight. Another local guy who is into M1As has been selling the MicroSight for them for some time, I don't know how he got around the alignment issue.

It's amazing to be able to literally see the machine marks on the front sight post as well as a clear 600 yard target. However, this system doesn't work for everyone. I don't know if they didn't have a square sight or what but I do know people that don't like it.

For disclosure I worked with the development of the MicroSight and have no vested interest in the product.

 

[hps1]

Fascinating stuff, Howard. Unfortunately too late to do me any good but I would have loved to have had that kind of vision while still able to shoot competition.

Thanks so much for sharing!

Regards,
hps

 

[FrankNatoli]

Edarnold: approximately ten years ago, I began to have some nasty intraocular floater problems, followed by flashing lights indicative of a retina in the process of detaching. Made a bee line for a retina specialist, who confirmed a loose [but not detached] retina, which he ably repaired with a laser, some 240 rivet bursts. Since that time, no more flashing lights, but floaters remain an annoyance. Since then, I have annual visits to the retina guy, including one earlier this year. I would like to think that in addition to micro examination of the retina, he also was looking at the cornea, and said nothing about a cataract. I'll give his office a ring tomorrow to check.

I would like someone, preferably an optical/ophthalmologist expert, to explain the visual phenomena that I am experiencing. The worst frustration is, when I can see the target, I can shoot pretty damn good, Master class. But I haven't shot a Master score in almost a year, all because I can't see the target.

 

[Ignition Override]

A friend who retired from a military rifle team gave me a spare can of Sight Black.

 

[AlexanderA]

Sounds like early symptoms of cataracts.

 

[FrankNatoli]

Thinking more about the symptoms, my suggestion of refraction cannot be correct, because that requires light going through [not bent around] different density mediums. But perhaps glare, as one poster suggested, is the problem. Distant point sources of intense light, e.g., car headlights at night, are obvious sources of glare. Perhaps so are distant target whites, which act like headlights, with glare interference from the front post saturating the aiming black. Anybody have any positive experience with polarized lenses to eliminate this kind of glare?

To those posters who have warned about cataracts, you may be correct, I will drop a letter to my retina guy, who checks me annually, after having had a repaired loose retina [asymptomatic after repair].

 

[Nathan Detroit]

Frank,

I think the phenomenon you are thinking about is diffraction, rather than refraction as you pointed out. Light will bend when going around sharp corners and that is known as diffraction, IIRC.

 

[FrankNatoli]

Nathan: after reading your post, I have read up on diffraction ad nauseum. Unfortunately, most of the literature talks about diffraction effects of apertures, though also mentioning that obstacles [e.g., front sight post] also cause diffraction. The only "help" I could find is that in photography, the wider you can open a lens [the aperture], the less the diffraction. Perhaps the obstacle corollary is that the smaller you make the obstacle [front sight post width], the less the diffraction. So I'm back to giving my 03 Springfield with its thin blade sight a try. Not that I would compete with an 03, but the 03 will prove whether minimizing the front sight width is helpful in reducing diffraction.

 

[AlexanderA]

Try this test: Look through a spotting scope at high power (30-40X or higher, with a small exit pupil). If you see a black spot or area in the center of the field of vision, you most likely have a cataract. If the cataract is bad enough, you'll see the black spot when looking through any pinhole, such as a receiver peep sight. (I had exactly this symptom, and it disappeared after I had my cataract surgery.)

 

[taliv]

Very interesting info. Thanks guys. I'll have to remember this thread in 20 years.