Lenses and apertures

[Jason]

This has gotten me to thinking about getting more serious about my sights on my cowboy silhouette rifles. Before we spend the money and time, does anyone know of any reason that a rear sight with a lens in it wouldn't be legal for NRA cowboy silhouette matches?

[Innocent]

Jason,
Robert Massey shot the 2010 Nationals with a lens.
Mary

[Bob259]

However Mary.... last year Fiber Optic sights were considered legal also. I'm sure someone will bring this up to the NRA and they will ban them as well using the same flawed reasoning they did with the Fiber Optics. Before I go spend money on lens for each of my lever rifles I'm with Jason, to error on the side of caution on this one.

[Jason]

Yeah.. I just picked up a couple new sights and am probably going to get a Merit adjustable aperture or two for them. My decision is buying the model that can't take a lens from Brownells, where I get discounts for my C&R FFL, or the model that can take a lens straight from Merit for twice the price plus the cost of a lens from Art or someone else. If I go with the model with the lens, I'll probably only buy one and just move it from gun to gun since it will cost so much counting the disk itself and the lens.

[ppkny]

If everyone would stop talking about this as if.....we are doing something illegal it will be. Don't you think it's just like a bi-focal in a pair of glasses. Are they going to outlaw eyeglasses next.
ppkny

[Innocent]

All, Robert had Greg's blessing at the nationals....but that doesn't mean that he will not change his mind when someone looks at him crosseyed. And yes Glen Ring, that includes you! I feel that this is nothing more than a pair of shooting glasses...how it is worn is irrelevant, but then I have been known to take Greg to the mat on more than one challenge and will probably do more before he is gone.

Mary

[Bob259]

........... but then I have been known to take Greg to the mat on more than one challenge and will probably do more before he is gone. Mary

Naw, don't believe it... remember your INNOCENT

[boats]

I don't see a word in the rule book about corrective lens. There is 13.1 Disabled shooters, were you can petition the silhouette committee to allow devices that overcome handicaps. My eyesight is a handicap for sure. Might mention it to a friend of mine on the Silhouette committee, it may have come up before.

On the Merrit with a diopter not a big risk for me since I shoot other iron sight matches were they are specifically allowed. However on my Schuetzen rifle have a diopter and don't use it. I suspect it's not a good one or the + is not correct for my eyes.

Boats

[cslcAl]

Boats, The wording for corrective lens is not in the current rule book. There was a addendum distributed to the match directors last year or the year before stating that corrective lens are legal in the rear sight only. The same wording is listed on page 69 of the 2010 Cowboy Nationals program under other items pertaining to Cowboy Lever Action Silhouette Rifles item D. IT IS RIGHT UNDER ITEM C. FIBER OPTIC SIGHTS ARE ACCEPTABLE !!!!!!!!! Al

[Jason]

After thinking on this a bit more, I have more questions if you have time to answer them. First, is the "power" measured in diopters on a lens the same as magnification power that I'm accustomed to with spotting scopes and binoculars or is it how much it adjusts the focus like focusing a camera lens? The descriptions here and logic seem to suggest that it isn't actually magnification but only focus adjustment. If that's true, are the "computer reader" glasses that are advertised as low-power computer reading glasses actually adjusting focus or do they actually magnify also? I tried a pair out today and they looked like they magnified the image more than changing the focus of it. I hope it was just in my head but it definitely confused me.

[RBriscoe]

Merit makes a version of the rear aperture sight which will take a lens carrier manufactured by BJ Jones. He has a page that discusses the lens strength as a function of distance & etc. http://bjonessights.com/power.html

I do not think his web site has much detail about the lens carrier for the Merit disk, but you can get the lens of your choice from him to go in it and screw it on to the merit...it is a longer version so you have to order the right Merit in the first place. I am told that the lens carriers are easily changed at the range, but the lenses themselves are not easily change in the carrier while at the firing line so you may want to have two if you find that you need a different correction in different lighting conditions.

I need to go ahead and order one of these for myself. You may also find that you need a little stronger correction than suggested as the match progresses because the eye will tire and not be able to stay in focus as well as it did at the start of the match. Remember, this is permissible on the rear sight only in CLA, unlike some other disciplines which allow it on the front sight.

There are a lot of different opinions about where the eye should focus between the front sight and the target. You simply have to find out what works best for you, but do not let the optometrist talk you into getting a correction which makes the front sight "perfectly sharp".

Rick

[ShootingSight]

Jason,

Diopter is a measure of how far a lens will adjust your focus, like a camera. It is not a measure of magnification. That said, positive power lenses will magnify, but the amount of magnification is a function of both the diopter, and also the distance from your eye (called the vertex distance - if youwant to google it). This is why long range shooters put the lens in the front sight. If you get reading glasses, you can move them away from your face and see the image grow, though with the powers you use for shooting, and the relative proximity of the rear sight, the magnification will only be a few percent.

A plus diopter lens is exactly like drug store, or computer reading glasses, the issue is just finding the right power. Reading glasses usually are much too strong to shoot with, as they start at minimum 1.25 diopters. This is so your focal point comes in to arm's length for reading. However, I was once at Staples, and they had some +0.5 glasses in a funky orange tint. For $20 it is a cheap experiment you can try if you can find them.

Art

[ShootingSight]

Rick,

You are exactly right. You do not want to focus 'on' the front sight, and I've run into more than a few cases where an optometrist who does not understand the needs of a shooter has gotten them a lens that gives a great front sight, but no target. Your depth of field ranges from some distance on the close side of your focal point, to some distance on the far side of your focal point. If you set your focus 'on' the front sight, the part of your depth of field that is on the close side of the focal point is wasted, and the range of DOF that is beyond the focal point won't go as far toward the target as you would like. You want to set your focal point so the front sight falls on the near edge of your depth of field, which means you want to focus beyond the front sight.

The question as to where to balance the focus between the front sight and the target is obviously open to personal preference, but I can say that for Service Rifle, I've used test lenses with a lot of shooters, and by far the lens that they end up selecting to get their best sight picture is the one that the hyperfocal calculations predicted. That is for a round bull though. With odd shaped silhouettes it remains to be seen if people want to keep a little more focus on the target.

When you go through the optical math, focal point is not affected by the brightness, so you should not need a different lens for bright/cloudy days. You should also not have to change lens because of eye fatigue. If you are getting eye fatigue, it means ou were not using enough lens in the first place, so your eye had to make up the difference that the lens was not providing. If you get the right power lens, your eye will stay relaxed, and you will not get eye fatigue. The mistake I see people making is assuming that since I'm young, I don't need a high power lens, a slight lens will do. This is not the case. There is an ideal focal point you need to get to, which is driven by barrel length. If you are young, you can get away with a mild lens, and your eye muscle makes up the difference. As you get older and the eye can no longer make up the difference, you graduate to a stronger lens. The real answer is that your ideal focal point has not moved,so you want to get the lens that gives you that focal point, regardless of if your eye is capable of making up the difference. Even for a young shooter, this will save eye exertion and keep your sight picture more consistent.



Art

[Tlee]

Fwiw, I've had some luck (with some assistance from my optometrist) using a "half or 1/4 script" that gives me the focus I need on the front site while still being able to see the targets somewhat clearly.

Being a bit of a skinflint I was concerned with costs of doing such an experiment and found zennioptical.com to be a great source for prescription polycarbonate lens glasses relatively cheap (couple/3 weeks turnaround). The couple I ordered as an experiment were $20-25/pair. They're not quite the $100+ quality of frames, but for "shooting glasses" they are a good deal.

- Tim

[JohnHenry]

I am the shooter Art Neergaard mentioned as asking for one of his rectangular rear sight apertures. I called Greg Connor's office about the permissibility of using this sight in the national competition. Their reply is they cannot allow them in competition without approval of the silhouette committee, which meets just once a year in November. Greg ask that I send a letter and all pertinent information about the sight to the committee so they can rule on it at the Fall meeting.

I'm still going to try the sight at a local match to see how much improvement in sight picture it affords. I will report back to the forum when I have done that. One aside: Jonathan, who works with Greg, commented that $80 for the sight smacks of an "equipment race." This is comical in light of the fact that I just saw a Marlin Cowboy in .357 sell for over $1,100 on Gunbroker.

Jim Luke