Iron sights and How to Use Them (Is there an eye doctor in t

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NCST8
Posts: 74
Joined: Sun Mar 14, 2004 1:31 am
Location: Morrisville, NC

Iron sights and How to Use Them (Is there an eye doctor in t

Post by NCST8 »

Iron sights are very simple. But, most people struggle with them.

We know that the focus should be on the front sight. While keeping the sights aligned, break the shot smoothly in the aiming area. If you do that correctly, you get a good result and generally a good score.

If you don't have perfect vision or conditions, this gets a lot more challenging.

To help, we have corrective lenses that more easily allow focus on the front sight. Tints can help maximize contrast between the white of the target and the bull. Then, we have irises.

What is the proper use for an iris?

I have access to an indoor range that has pistol bays to 50 yards and a rifle bay up to 100M. The lighting is really challenging. Some targets are really bright and others dark. Some points have a spotlight directly over the pistol, and others are much more dimly lit. Some days, I wind up with brightly lit sights and a dark target. Other days, I wind up with a brightly lit target and really dimly lit sights.

What is the correct way to compensate for too much light from the target bending around the front sight?
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Gerard
Posts: 947
Joined: Thu Mar 10, 2011 2:39 am
Location: Vancouver, Canada

Post by Gerard »

Not an expert, but I'd guess that a shading lens in front of a reasonably small aperture would help. Not a coloured filter, but a sunglass type lens to reduce the total light being admitted without having to stop the iris down so small that distortive effects start appearing because of the small hole.

And if ambient lights are sometimes in your eyes, consider a baseball cap type brim and/or side shields.
Rover
Posts: 7004
Joined: Sat Nov 15, 2008 4:20 pm
Location: Idaho panhandle

Post by Rover »

I was told by Don Nygord when I bought Champion shooting glasses from him, that the purpose of the iris was to maintain a uniform "pupil" diameter, NOT to increase depth of field (making sights and bull sharper).

Because eyes vary in shape your vision changes with larger and smaller pupil diameter. The iris creates a single, unchanging pupil under different lighting conditions.

The iris can make the bull and sights sharper, but I see no advantage in that since it takes your mental focus away from sight alignment. Changing the iris diameter while shooting can also change your zero since it changes the apparent size of the bull.

BTW I just had a new prescription lens installed in my glasses. I'm glad I did. It removed some astigmatism and sharpened the front sight.
Gwhite
Posts: 3296
Joined: Sat Sep 04, 2004 6:04 pm
Location: Massachusetts

Post by Gwhite »

As my eyes have gotten older, I am constantly struggling to maintain the sight picture I used to get with ease. I'm almost 60 now, pretty nearsighted, have astigmatism, floaters, presbyopia, and the beginnings of cataracts. You young guys should enjoy it while you can. First, let me describe what the (for me) ideal visual set up is:

You have to be able to focus on the front sight, preferably without having to tax the muscles in your eye very much. Depending on the lighting, your depth of field will vary as your pupil changes size. Ideally, the rear sight should be reasonably sharp. If the depth of field is too great, and the target is too clear, it makes it harder to concentrate on the front sight.

Here are my thoughts on shooting glasses:

Corrective Lens: This is used to set the eyes relaxed focus. I find it useful to make sure that I can't fully focus on the target, but without making it too blurry. NOTE: the tolerances of most optical shops are pretty coarse. Getting lenses that are REALLY accurate to less than +/- a quarter diopter is difficult. I've measured a lot of my lenses, and they are not at all consistent. If you shoot with an aperture, it's only the center that matters. A full lens focal length measurement doesn't really tell you what you need to know. My eye doctor has let me use a machine that use a small light so you can measure at different points on a lens. However, the smallest increment it can measure is 1/4 diopter. You can buy shooting glasses lenses in 1/8th diopter increments. That is almost meaningless unless you can verify it independently, or are willing to spend a lot of time swapping lenses in & out to see what difference it makes.

Aperture: If this is smaller than your pupil for the lighting conditions, it will control your depth of field. If it's bigger, it can adjust the light hitting your eye, which will affect your pupil size, so it can work two ways. I find it much simpler to operate with it small enough that the aperture is running the show. I like to adjust mine so the front sight is crisp, the rear sight is reasonably sharp, and the target is slightly blurry. Depending on the light & target distance, that can be a tricky balance to find. If you have to crank it down to the point that the target is in focus before your rear sight is, you need to adjust the corrective lens to bring the overall focus in closer. This year I occasionally have problems with a double-image of the target, where I get a blurry target, with a slightly fainter blurry target offset to one side. I think this may mean my astigmatism is no longer properly corrected. Cranking down on the aperture can reduce this. Call me silly, but I really prefer to shoot at only ONE black.

Filters: I use "neutral density" (grey) filters. I have an ND20, ND40, ND60 and ND80, with 80 being the darkest. If there is a lot of light (outdoors on a sunny day, especially), my pupil will crank down to the point where my aperture is no longer controlling my depth of field. I've also had problems recently with getting glare off brightly lit targets that tends to wash out the edges of the sight. This may be from my contact lenses or cataracts, but whatever it is, a darker filter can help. I've found that I get the best sight picture (and the best scores) when I use a filter that is a little darker than what I would want for normal vision. Any darker than that, and I just can't see anything clearly.

The best setup for me is quite different for shooting indoor air pistol & outdoor free pistol. Each indoor range is different, and the lighting outdoors depends on the range, time of day & the weather. I rarely shoot indoors where I feel I need to add any filtering. Outdoors, I hardly ever shoot without at least the weakest filter. Being able to adjust for rapidly changing light when clouds move in & out makes the difference between a decent sight picture and being absolutely unable to focus on my front sight.
NCST8
Posts: 74
Joined: Sun Mar 14, 2004 1:31 am
Location: Morrisville, NC

Post by NCST8 »

Thanks for the responses. These are by far the best I have received. I posted this question in a number of places.

Evidently, everyone has really good eyes, they never shoot irons, or no one else knows either.
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