Eye problem? Rear peep changes diameter.

[Simonpie]

So, a new question for me.

Lately, when I hunker down to shoot, right as I'm breathing and steadying out, the rear aperture diameter appears to shrink, then grow just a touch, then stabilize. From the timing, it seems just like my iris (in my eye, not the sight) is adjusting. It isn't necessarily a problem, but it seems odd my iris is controlling the diameter of the apparent hole. I'm worried my eye could also be controlling the location of the apparent rear sight, making my eye the true sight. Make sense? Is this an eye relief issue?

I shoot a league that hits a different 50 ft range each week. Lighting conditions vary quite a bit, if it matters.

I recently had a different problem caused by new glasses frames, but this is happening with my old glasses and setup.

[Tim S]

Could it be that you are moving your head fractionally along the cheekpiece? Back a bit (making the aperture appear smaller), then forwards (a bit too much as the aperture looks too big), then backwards into the right place.

[KennyB]

I found that my rear sight iris varied in apparent size too - outdoors it seemed quite tight to the foresight but indoors it seemed much bigger. I put it down to the different light levels and my eye's iris opening up.
I now use a slightly longer eye relief for shooting indoors to compensate.

I also sometimes train with a mirror in the rearsight to ensure that I'm looking through the peephole in the same way each time.
I subscribe to the idea that the rearsight is there to assist you to line up your eye, the foresight and the target - so yes, I think the eye is the true sight.
Adjust the rearsight and you also have to adjust your eye/head position.

I don't think it's a problem but it's good to be aware of it.

Ken.

[Simonpie]

I also sometimes train with a mirror in the rearsight to ensure that I'm looking through the peephole in the same way each time.
I subscribe to the idea that the rearsight is there to assist you to line up your eye, the foresight and the target - so yes, I think the eye is the true sight.

Ken.

Interesting. Can you describe your mirror setup? It has to allow light in between the sight and the mirror right?

[KennyB]

It's one of these:
http://www.edinkillie.co.uk/ecatalog/ce ... Path=44_46

Ken.

[RossM]

You are right about it being your iris. As you look around the eye responds to the light conditions by opening and closing the iris. More light iris closes. The iris is in front of the lens in your eye. As the iris (which is the pupil as well) closes, the effect of the lens becomes less and less. What in effect happens is the focal length of the eye moves out towards the iris. This has the effect of restricting the field of view through your eye and it manifests itself by also making the aperture appear smaller. It is a bit like a telephoto lens but on a smaller scale.

I see this difference exaggerated between shooting indoor and outdoor. Outdoor the iris is lots smaller and the field of view through the aperture really shrinks.

[ShootingSight]

Your eye's iris does not influence your vision when shooting. The rear aperture is about 1mm, and your eye's pupil can only go down to 3-4mm on a bright day, so the rear iris is so small that what your eye does is not relevant to your target image.

Now, there is a presumption that when you get in position, the projected image coming through the aperture falls entirely within the part of your eye that is inside the pupil. If you move your head out of alignment so that the image is bounded partly by your aperture, and partly by your pupil, this will make the entrance pupil to the optical path smaller than you had intended.

The other thing to consider is what your eyebrows are doing. If you squint as you shoot, it is easy for your eyebrow, or your eyebrow hairs to dip into your optical path. Consider trimming your eyebrows if they are very bushy.

[timinder]

If you say the eye's iris has no effect on your vision - try this:
look through the sights (both eyes open) towards a relatively bright wall and note how much of the front sight is within your field of vision.
Now cover the non-aiming eye with something opaque and see what happens to your field of view...
How do you explain that effect?

[ShootingSight]

Your two eyes do react together to brightness. If one is looking throught he sight,nad the other looking around the sight, if you change the lighting level on the non-aiming eye, it will cause the pupil of the aiming eye to react.

However, the depth of field of the aiming eye is driven by the entrance pupil to that eye, which is the projection of the smallest diameter aperture onto the cornea surface. And that will not change as your pupil changes, since the pupil is not the smallest diameter aperture in the optical system.

[tiggerfinger]

Whilst we can debate the exact cause, the problem is real. I really struggle when shooting outdoors, it takes a lot of concentration with an apparently tiny rear aperture. So can anyone suggest a way of alleviating the problem.

[Martin Catley]

Maybe if you could tell the group what size rear peep you are using and roughly what your eye relief is? As has been already stated does your eye relief vary it is possibly better to cover your basic position before going into the makeup of your individual eye.

[tiggerfinger]

I use a 1.0 rear iris both indoors and outdoors and generally keep a yellow filter on for both. I've tried using a polarising filter but it made no difference. I wear shooting glasses so my eye relief is as close as I can get the lens to the rear of the iris without actually touching.

[3P-Walther]

I believe ShootingSight is correct. The eyes work together and try to have same-size pupils. In indoor shooting, the light is usually dimmer than outdoor, so the pupils are large to start with. When you look through the sight you will see the aiming eye change in response to the non-aiming eye being suddenly blocked by the blinder. That is normal. It does so out doors too, but less and so not noticed, generally. Changing the blinder color for the non-aiming eye can help equalize the eye pupils, which helps prevent eye fatigue.