Rear Iris

[redschietti]

Everything we read says don't make the rear aperture too small. Especially if your old! LOL My eyes are getting close to 50, the rest of me isn't. I challenged myself to take up shooting 2 years ago and figuring out how to see, and how to see for a whole match has been my biggest problem. Just in case anybody cares my match PB is 1597/1600 NRA prone.

I seem to see best outdoors with rear at 0.7. Match Sunday I closed it to 0.5, and shot my best ever scores, with a great sight picture. It was only a 45 shot match, so I cant say my eyes would have held up for a full 1600.

I don't like bucking what people with more experience and knowledge say, but I know bigger doesn't work for me. What am I missing? Is bigger but further from my eye the answer?

[mtncwru]

Part of that equation has to do with your eye relief, too. I would venture a guess that, if you're doing that well at 0.5mm, your rear iris is likely SUPER close to your eye. Someone with a better knowledge of optical physics can likely weigh in better than I can, though.

Edited To Add: Clearly if it works for you, then run with it. But as others will, no doubt, chime in, eye fatigue over a 1600, and the cumulative eye fatigue over a weekend or a 4-day does matter, and may be accentuated by your narrow iris setting.

[Tim S]

Do you have a lens for shooting?

A very small aperture will narrow your depth of focus, so the foresight and target appear sharper. If you have naked eyes, this would obviously help. However the trade off is a darker sight picture; this may be OK outdoors on a bright day, but if it's overcast or you're indoors the sight picture may be too dark (poor aim and tired eyes).

This is where a shooting lens is really useful. The lens focuses your eye at a point where the foresight is sharp and the target visible enough to aim well, so you don't need a really tiny aperture to achieve a good sight picture. The aperture can then be set a little larger for a brighter picture.

Out of interest what is your eye relief?

[redschietti]

I normally wear contacts. Tried contact with shooting lenses, tried contact with altered prescription. Contact with +50 added to prescription was good but dry eye caused problems over the course of a match. Switching to no contact, with prescription dialed into fancy expensive rear iris seems to be working well this year. Also using eyedrops.

My eye relief must be really close, as when my head position is where I want it, my eyebrow almost is touching.

It was very bright sun, full on the target, when I shot with 0.5.

[KennyB]

with prescription dialed into fancy expensive rear iris seems to be working well this year.

Do you mean that you are using a magnifying diopter (Centra, Gehmann or similar)?

I think different rules apply to them. When I recently shot a friends rifle with one of those, I found I was closing the iris down to well under 0.9 for the sharpest sight picture. With a normal iris I'm always well over 1.1 and sometimes up to 1.5........

K.

[redschietti]

Yes, a magnifying diopter. Maybe that's it!

[KennyB]

When I shot my friends rifle (he wanted to know if it shot or whether it was him - it was him) I initially set the iris to where I would normally have it and dialed in the focus to give a sharpish foresight but the aiming mark was REALLY grey and indistinct. the only way I could get an acceptable sight picture was closing down the iris.

I did used to use one of these irises early on but abandoned it about 4 years ago so I could shoot ISSF. From memory it was usually around 0.9. I also worried that I was flying in the face of received wisdom but didn't have the experience or confidence to go my own way.
If I were to go back to it now, I wouldn't worry about the iris size if the sight picture and results at the target were good.

I often think that much of the received wisdom that we are told comes from a bygone era and as things have evolved over the years, some of the "rules" no longer are relevant.

K.

PS. since ditching the diopter my shooting has gone to a whole new level - not that it's the only reason but it may well be a part of it.

[patriot]

Magnification is not enough if you have an astigmatism. It is better to use shooting frames with a custom lens. Since they are cheap I keep several +/- my current adjusted prescription for verification. I'm at the age were my nearsightedness is improving (don't want to know what comes next). With the shooting frames, you can rotate the lens to double check your astigmatism too. My last eye checkup the doc said my astigmatism had not changed enough to notice. I told him 15 degree clockwise. He said I was not normal... but correct.

Comparing iris openings is meaningless without including the distance from the eye. The iris opening controls the amount of light entering the eye, so isn't it the obvious adjustment for changing light conditions? Filters are all or nothing.

Mark

[skylark]

The iris opening controls the amount of light entering the eye, so isn't it the obvious adjustment for changing light conditions?

Maybe. I mean, yes it does control the amount of light entering the eye but it also affects the sight picture. In extreme cases, you probably don't want a tiny pinprick of a rearsight aperture through which you can't even see the outside of the foresight just because it produces the same amount of light that 1.1mm does in normal conditions.

[efoleyjr]

When I shot my friends rifle (he wanted to know if it shot or whether it was him - it was him) I initially set the iris to where I would normally have it and dialed in the focus to give a sharpish foresight but the aiming mark was REALLY grey and indistinct. the only way I could get an acceptable sight picture was closing down the iris.

I did used to use one of these irises early on but abandoned it about 4 years ago so I could shoot ISSF. From memory it was usually around 0.9. I also worried that I was flying in the face of received wisdom but didn't have the experience or confidence to go my own way.
If I were to go back to it now, I wouldn't worry about the iris size if the sight picture and results at the target were good.

I often think that much of the received wisdom that we are told comes from a bygone era and as things have evolved over the years, some of the "rules" no longer are relevant.

K.

PS. since ditching the diopter my shooting has gone to a whole new level - not that it's the only reason but it may well be a part of it.

Ken,
Are you saying that when you stopped using an "Eagle Eye" that your shooting got better? What power EE were you using? What is the normal state of your Vision? Thanks

Ed

[KennyB]

When I shot my friends rifle (he wanted to know if it shot or whether it was him - it was him) I initially set the iris to where I would normally have it and dialed in the focus to give a sharpish foresight but the aiming mark was REALLY grey and indistinct. the only way I could get an acceptable sight picture was closing down the iris.

I did used to use one of these irises early on but abandoned it about 4 years ago so I could shoot ISSF. From memory it was usually around 0.9. I also worried that I was flying in the face of received wisdom but didn't have the experience or confidence to go my own way.
If I were to go back to it now, I wouldn't worry about the iris size if the sight picture and results at the target were good.

I often think that much of the received wisdom that we are told comes from a bygone era and as things have evolved over the years, some of the "rules" no longer are relevant.

K.

PS. since ditching the diopter my shooting has gone to a whole new level - not that it's the only reason but it may well be a part of it.

Ken,
Are you saying that when you stopped using an "Eagle Eye" that your shooting got better? What power EE were you using? What is the normal state of your Vision? Thanks

Ed

Hi Ed,
not an eagle eye (lens in the foresight), a magnifying diopter type iris rearsight (I have 2 Centra ones sitting in a box somewhere).
I did experiment with 1.3x and 1.5x eagle eye lenses but found no real improvement over no eagle eye at all and since I wanted to shoot ISSF it was a bit pointless. Maybe at some time in the future I'll give them another try.

My distance vision is better than 20/20 (?) with only a small -0.25 astigmatism but at 56 I now need +1.5 reading glasses.

Coming off the diopter was scary at first as everything looked so SMALL - but SCATT showed I was aiming more consistently so I persevered and now everything looks huge. Surprising how our brains adapt...

Ken.

[efoleyjr]

When I shot my friends rifle (he wanted to know if it shot or whether it was him - it was him) I initially set the iris to where I would normally have it and dialed in the focus to give a sharpish foresight but the aiming mark was REALLY grey and indistinct. the only way I could get an acceptable sight picture was closing down the iris.

I did used to use one of these irises early on but abandoned it about 4 years ago so I could shoot ISSF. From memory it was usually around 0.9. I also worried that I was flying in the face of received wisdom but didn't have the experience or confidence to go my own way.
If I were to go back to it now, I wouldn't worry about the iris size if the sight picture and results at the target were good.

I often think that much of the received wisdom that we are told comes from a bygone era and as things have evolved over the years, some of the "rules" no longer are relevant.

K.

PS. since ditching the diopter my shooting has gone to a whole new level - not that it's the only reason but it may well be a part of it.

Ken,
Are you saying that when you stopped using an "Eagle Eye" that your shooting got better? What power EE were you using? What is the normal state of your Vision? Thanks

Ed

Hi Ed,
not an eagle eye (lens in the foresight), a magnifying diopter type iris rearsight (I have 2 Centra ones sitting in a box somewhere).
I did experiment with 1.3x and 1.5x eagle eye lenses but found no real improvement over no eagle eye at all and since I wanted to shoot ISSF it was a bit pointless. Maybe at some time in the future I'll give them another try.

My distance vision is better than 20/20 (?) with only a small -0.25 astigmatism but at 56 I now need +1.5 reading glasses.

Coming off the diopter was scary at first as everything looked so SMALL - but SCATT showed I was aiming more consistently so I persevered and now everything looks huge. Surprising how our brains adapt...

Ken.

Ken,
Thanks for the info. I myself at 72 and eye sight of -2.75/+1.75@51* constantly fight to get a good sight picture using a 0.5d eagle eye in the front. I seem to have an acceptable sight picture for the first 3 or 4 minutes of each string but the sight picture gives out quicker and is blurrier much faster than early in the string. My reason for the original question was I was thinking that I may get a clearer sight picture if I did not use an eagle eye and your post sounded like that was your experience. You are right about the bull being VERY small without the eagle eye, it is hard to believe that the bull looked that small when I was young. I would be interested in your opinion on of it would make since to shoot without an EE and expect to benefit from the change. Thanks
Ed

[ShootingSight]

Unfortunately, optical physics and old wives tales are difficult to tell apart.

Old eyes needing more light is plain wrong. There are a few medical conditions where it is true, but they are rare. The true answer is that a smaller aperture will give you a better depth of field, so you want as small as you can. The limitation is when the image starts to go dim because of inadequate light. You judge focus both based on blur, and on contrast difference, so if you start to get the image dim, it might be in focus, but without the contrast it is difficult to see. THe myth about old eyes needing more light comes from reading menus in dim restaurants. Your brain learns that if you turn up the lights, you can read better, and so you believe more light is better focus. In reality, what is happening is that more light makes your pupil constrict, thereby giving your eye a greater depth of field. In shooting, you don't have the biological reaction of aperture size varying based on light, so you can manually set the aperture smaller.

Optically, there are two elements you want: a big depth of field, which you get with a small aperture, and you also want a relaxed focal point which centers that depth of field between the front sight and the target. This is accomplished by adding +0.50 diopters to any distance correction you have. If you have perfect 20/20 vision, all you need is a +0.50 lens. If you have a distance correction, even a slight one, you take that lens value and add +0.50 to it.

Gehmann and Centra both make rear iris with adjustable focus. I'm on the fence about these. I love them, because you can just dial them in while looking through them, however it is not an adjustment that should change frequently, and once you know the optical math to calculate what you need, you may as well just buy the correct lens and be done with it. So I see them as an added complexity and cost that often is not needed. Also, they typically only correct spherical errors in your eye, not astigmatism errors (I think Gehmann made one that did astigmatic corrections, but it was a beast with 4 lenses that you needed to dial and orient .... you needed a degree in optics just to follow the instructions).

All lenses will both shift your focal point, and will magnify somewhat, so trying to define a lens as a magnifying lens, versus a focal adjustment lens is really one and the same thing. How much of each a lens does is driven by lens power, and distance of the lens from your eye. Eagle eyes are +0.25 diopter and +0.50 diopter lenses that are put in the front sight. From a focus perspective, they are a poor solution - they are too close to the front sight to help you see it any better, and they will blur the target, so you see that worse as well, however their distance from the eye means they magnify about 150%, and a lot of people find this makes it easier to see the number boards.

How you execute the lens has options. Adding it to the contact should work, but if it causes dry eye, that's not good. I make a lens holder that can add the lens into the rear sight, or you can get shooting glasses with the prescription dialled in. Glasses are the least favorite, as you need to look through the lens at a strong diagonal in prone, and that introduces astigmatic errors in the lens.

Aperture distance to your eye does not really make much difference so I would not worry about that - much better to get it so you are comfortable with a consistent cheek weld.

Art Neergaard
ShootingSight llc