Rear Aperture Sights and Astigmatism

[TuckerJ]

I've been somewhat bitten by the iron sight bug after doing some shooting with my CMP 40X and Redfield Olympic sights. I'm 39, have quite a bit of astigmatism, and am also near sighted. I wear Standard, single vision glasses to correct my vision. Sometimes I have a good clear sight picture. Other times I really struggle to have the target (A23 at 50 yards) in focus at all. I seem to have no problem getting the front sight in clear focus. I actually wish I could let the front sight be slightly out of focus and allow the target to be in focus better.

At times the target will be in very good, crisp focus, but it seems to be a fleeting image and then blurs out again. I understand the target being slightly out of focus as normal, but I'm talking out of focus to the point of it almost disappearing from view at times.

I'm wondering about an adjustable rear iris to see if it would help with this. Our range is covered and I wonder if I need a larger rear iris to let more light in to help me see.

In researching, I see that Gehmann has rear irises with 1.5x magnification that allow for distance correction. I thought this might be the answer to adjusting the iris, and then correcting where my focus lands to balance the target and front sight focus. Then I read that these will not work at all for those with astigmatism. My question is if I continue to wear my prescription glasses to (mostly) correct my vision, will I still see some benefit from the rear irises with -4.5-+4.5 correction? Or is there something about the 1.5x magnification that will wreak havoc with my astigmatism, even if keeping my glasses on?

My vision changes year to year, so I imagine when I get new glasses my sight picture is pretty good, but as my prescription ages it gradually gets worse. I'm wondering if a sight like this would help me tweak things for a good image.

I don't want the expense of the sights that adjust for astigmatism, or the hassle of dealing with the round lenses that attach to the rear of the sight with a rod.

If the sights with +/- correction are counter productive to those with astigmatism, I'll probably just get an adjustable iris and leave it at that.

Final question - is it worth the slight upgrade to get one with color filters or do they not make a significant difference?

 

[68Hoyt]

Look at the Gehmann 579 , I am not a competitive shooter , I got one because of my astigmatism ( I had corrective surgery several years ago but still not perfect ) and it seems to help

 

[Tim Slater]

Tucker,

That's a lot of questions!

Normally, an astigmatism can be accomodated quite simply with spectacles. The lens can also correct distance vison too; typically a shooting prescription is distance +0.5 (this extra makes the target more visible without being in focus).

However, if your eyesight is changeable, multiple lenses gets expensive. In this case a dioptre eyepiece may work out cheaper. Practically, yes you can use regular specs (with astygmatism correction) with a dioptre eyepiece. If you're shooting in competition check the rules allow this.

As an aside regular glasses may not line up properly when shooting, particularly in Prone; you'll find you're peeking through a corner. You could have a lens made with just cylindrical correction, attach this to the eyepiece with a monoframe (Gehmann, Anschutz, or MEC) and use the focal adjustment in the eyepiece for distance, assuming your distance correction isn't more than +/- 4.5.

Colour filters can be really useful shooting outdoors. Grey will tone down bright light. Yellow enhances contrast in lower light. Polarisers cut glare in very bright light. The idea is to maintain a consistent level of light. Remember light affects how the apparent size of the target and the gap inside the aperture. Adjusting the rear aperture is another tool.

 

[Walt Krafft]

Tim covered a lot. My eyes were very similar to yours before I had cataracts fixed. Your regular eyeglasses will not be very good shooting with irons. You will end up looking through a corner and lose a lot of the correction. A pair of the adjustable shooting glasses will help a lot. When you have the lens made for it, make sure they mark the lens so you can have it rotated correctly. Don't waste any money on colored filters until you get things figured out with clear lenses.

 

[TuckerJ]

Great info guys. I don't shoot competition so I don't need to worry about being legal for various disciplines. At this point I've still been able to get good results shooting, but some days it feels more strained than relaxing to get a good sight picture. I've also noticed a good sight picture tends to give good results and if my sight picture struggles I sometimes get unexplained shots.

I'd rather not go to a dedicated monocle type lens (either as glasses or on the rifle/sight), though it may come to that someday.

As of now, I was wondering if I should just get the basic Gehmann 510 or something like the 530 or 570 with 1.5x and distance correction. It sounds like I wouldn't necessarily be at a disadvantage with more correction adjustment so I might consider springing for that. The 579 would probably be nice but trying to not spend too much on this right now.

At a minimum, I believe I'd be seeing some improvement just from a simple adjustable iris.

Certainly open to more responses if anybody else has their experience to add but appreciate the advice given so far.

Thanks,
Tucker

 

[Bluefink4895]

Tucker, regarding iron sights and focus. It is more important to have a clear front sight vs the bull. It's OK and normal to have a slightly fuzzy bull, as long as you can see your number boards. In fact, you don't want too clear of a bull, as you will bull gaze and lose focus on your front sight. Front sight is paramount when it comes to irons.

Regarding your vision issues, I've been in the same boat...and it hit me all at once when I turned 39. I was at a -6.5 diopter in my right shooty eye at that time. So, I had to get creative and learn.
Some key point:
The human eye cannot focus on 2 separate things at different distances at the same time (front sight and target). When you are younger, your eye muscles are stronger and your lenses are more flexible (eye muscles flex the lens to focus, especially up close). The focus change can be very quick when you are young, giving you the impression that you can focus on both. But....as you get older, this changes - Presbyopia will be your bane. Lens gets harder and muscle weaker. Consequently, your eyes will fatigue quickly, loosing focus on things closer to the eye (near). Get ready to need both distance RX and reader bifocals in your glasses. Being near sighted and having a stigmatism aggravates the situation. An Rx that corrects for sigmatism will reduce the fun houser mirror effect.
Some lessons learned...
For front sight clarity + a "decent" looking bull:
1) Put the front sight out as far as possible.
A) In a normal or corrected vision condition, the muscles that control focus are more at rest/less strained when at distance/infinity setting. It's up close where strain and subsequent strain occurs. This why folks use long sight extension and bloop tubes.
B) Look up Hyperfocal distance for best front sight distance position. Talk to Art Neegard at Shooting Sight.Com
2) Rear aperture size - go smaller to increase depth of field. This will allow easier focus on both front and target. But...go to small and you will loose light...which creates another set of issues. This is where a variable rear iris comes in handy.
3) Rear aperture Rx adjustment:
A) A rear iris that allows +/- adjustment can help. But they are delicate expensive creatures. The rule is + adjustment for better front, - for distance. Same as the Rx in your glasses.
B) Add a lens to your rear sight as mentioned in previous posts. With that in mind, you will need + adjustment, not - for front sight clarity. Normal rules of thumb +0.75 for 20" AR Service Rifle. +0.50 for M1A, Garand, etc, +0.25 for my 24" long match rifle.
4) Magnifier lens in front - this will make the bull bigger. Just like large print books for older folks. It's easier to see big things than itty bitty things. The only downside is that you will have to increase your front aperture size/adjust front sight location. In my case, I use a 0.50+ magnifier in front of an 8.5mm iris setting, all of this dangling on the end of a 12" bloop tube. But that is what works for me.

Hope this helps.

 

[SteveUrban]

Front sight focus is more important than a target in focus. Let the target be blurry.

 

[TuckerJ]

I believe with a monocle type lens on the sight, bloop tube extension, etc I could probably get a very nice, consistent sight picture. With that said I'm not sure if I want to jump into everything it takes to put that setup together yet. I'm mostly shooting OK as is. When I first got my 40x last year I shot some pretty consistent mid .3" groups at 50 yards from the bench and am still able to do that and occasionally better it. I'm doing about as well offhand and prone as I'd expect to do with my skill level, but I know my sight picture could be better, or at least less strained.

I understand letting the black bull go out of focus, but some days (lighting conditions maybe), it fuzzes out to the point of being very light gray and even almost disappearing. I don't shoot as well when this is happening. I can usually see it ok for a bit if I look at the target over the top of my sights, then look through the peep but sometimes I don't have long before I start to lose the target again. Interestingly I don't seem to have a problem keeping the front sight in focus. But if I can't see the bull, it's pretty hard to hit. I have a feeling I'm dealing with some eye strain. Our range is covered and I wonder if I need to open the rear aperture some to let more light in. Bright days tend to be better for me.

Still deciding if I just get a simple 510 that offers an adjustable iris or something like a 530 that gives some correction as well. I think I'm leaning towards the 530, for not a whole lot more money. I have a feeling anything will help and show me a usable improvement.

 

[68Hoyt]

So ,,,,,, an adjustable aperture is nice , but the magnification did not work very well for me , I have astigmatism / correction surgery / then have some uneven topography on the lens of my eye which causes some issues when peering through the peep ,
Some days it’s fine some days it’s frustrating ,
If you can find something that helps your vision all the time or most you will enjoy shooting a lot more

 

[Bottom Fodder]

I’ll take a clear front sight and blurred target over a blurred front sight and clear target and day

 

[danny]

I've been somewhat bitten by the iron sight bug after doing some shooting with my CMP 40X and Redfield Olympic sights. I'm 39, have quite a bit of astigmatism, and am also near sighted. I wear Standard, single vision glasses to correct my vision. Sometimes I have a good clear sight picture. Other times I really struggle to have the target (A23 at 50 yards) in focus at all. I seem to have no problem getting the front sight in clear focus. I actually wish I could let the front sight be slightly out of focus and allow the target to be in focus better.

At times the target will be in very good, crisp focus, but it seems to be a fleeting image and then blurs out again. I understand the target being slightly out of focus as normal, but I'm talking out of focus to the point of it almost disappearing from view at times.

I'm wondering about an adjustable rear iris to see if it would help with this. Our range is covered and I wonder if I need a larger rear iris to let more light in to help me see.

In researching, I see that Gehmann has rear irises with 1.5x magnification that allow for distance correction. I thought this might be the answer to adjusting the iris, and then correcting where my focus lands to balance the target and front sight focus. Then I read that these will not work at all for those with astigmatism. My question is if I continue to wear my prescription glasses to (mostly) correct my vision, will I still see some benefit from the rear irises with -4.5-+4.5 correction? Or is there something about the 1.5x magnification that will wreak havoc with my astigmatism, even if keeping my glasses on?

My vision changes year to year, so I imagine when I get new glasses my sight picture is pretty good, but as my prescription ages it gradually gets worse. I'm wondering if a sight like this would help me tweak things for a good image.

I don't want the expense of the sights that adjust for astigmatism, or the hassle of dealing with the round lenses that attach to the rear of the sight with a rod.

If the sights with +/- correction are counter productive to those with astigmatism, I'll probably just get an adjustable iris and leave it at that.

Final question - is it worth the slight upgrade to get one with color filters or do they not make a significant difference?

You probably can get the target in focus really well....if that's what you want.... You just go to your eye doctor and tell them that you want some super duper high power prescription corrected for infinity, but that's probably what they are already doing. Most guys that shoot irons well don't want that, but if you want that, that's up to you. Just remember, I'm NOT from the government, but I am here to help.

Danny

 

[danny]

Front sight focus is more important than a target in focus. Let the target be blurry.

It's not what he wants, though. lol

Danny

 

[TuckerJ]

You probably can get the target in focus really well....if that's what you want.... You just go to your eye doctor and tell them that you want some super duper high power prescription corrected for infinity, but that's probably what they are already doing. Most guys that shoot irons well don't want that, but if you want that, that's up to you. Just remember, I'm NOT from the government, but I am here to help.

Danny

Looking back at my original post I think I didn't explain this very well. I do understand the target is not supposed to be in sharp focus but the front site should be. I almost can't seem to change my focus to cause the front sight to blur even if I wanted to. It seems to generally be quite sharp. What I was trying to get at is if I could give up a tiny bit of that front sight focus and allow the target to be more visible that would seem better (and yes... I know the front sight should be sharp...).

My main issue is the front sight tends to be in pretty sharp focus but the target is often completely out of focus, sometimes to the point of almost not being able to see it at all. Sometimes the target ends up in crisp focus (probably too crisp), and sometimes it's about right. More often than I'd like though, the bull ends up being quite out of focus, more than I think is preferred. I have a feeling some of this comes down to me straining somewhat and trying to force myself to direct my focus "somewhere" that isn't necessarily natural.

I'm not exactly sure what's causing this, and I realize that an expensive and elaborate setup would probably make things a lot better. Since I don't compete, I'm hoping that there's a somewhat simple solution like an adjustable iris that will at least make things better. As is I'm doing ok, but I think I could probably do better, and feel a little more relaxed while doing it. If I could see a slight to moderate improvement from current state I'd be pretty happy.

 

[TuckerJ]

It's not what he wants, though. lol

Danny

I think if you'd read further posts in this thread you'd understand that what you say I'm looking for is not exactly what I'm looking for...

 

[TuckerJ]

So ,,,,,, an adjustable aperture is nice , but the magnification did not work very well for me , I have astigmatism / correction surgery / then have some uneven topography on the lens of my eye which causes some issues when peering through the peep ,
Some days it’s fine some days it’s frustrating ,
If you can find something that helps your vision all the time or most you will enjoy shooting a lot more

That's interesting. I've heard it both ways which makes deciding confusing. I imagine it's because everyone's eyes are different and unique, and respond differently. Probably need to just pick a direction and go with it and see how it works. An adjustable iris with no magnification or correction might be the safest bet, though I might always be wondering if correction ability would make it better yet.

 

[danny]

I think if you'd read further posts in this thread you'd understand that what you say I'm looking for is not exactly what I'm looking for...

I read further in. My question is this: Which do you want in focus, the target or the front sight?

Danny

 

[TuckerJ]

I read further in. My question is this: Which do you want in focus, the target or the front sight?

Danny

I want the front sight to be in focus. But I still want to be able to SEE the target. Sometimes just SEEING the target is not as easy as it should be. Or it's blurred enough that it's hard to tell when it's centered. Well past "slightly fuzzy."

 

[Bluefink4895]

Looking back at my original post I think I didn't explain this very well. I do understand the target is not supposed to be in sharp focus but the front site should be. I almost can't seem to change my focus to cause the front sight to blur even if I wanted to. It seems to generally be quite sharp. What I was trying to get at is if I could give up a tiny bit of that front sight focus and allow the target to be more visible that would seem better (and yes... I know the front sight should be sharp...).

My main issue is the front sight tends to be in pretty sharp focus but the target is often completely out of focus, sometimes to the point of almost not being able to see it at all. Sometimes the target ends up in crisp focus (probably too crisp), and sometimes it's about right. More often than I'd like though, the bull ends up being quite out of focus, more than I think is preferred. I have a feeling some of this comes down to me straining somewhat and trying to force myself to direct my focus "somewhere" that isn't necessarily natural.

I'm not exactly sure what's causing this, and I realize that an expensive and elaborate setup would probably make things a lot better. Since I don't compete, I'm hoping that there's a somewhat simple solution like an adjustable iris that will at least make things better. As is I'm doing ok, but I think I could probably do better, and feel a little more relaxed while doing it. If I could see a slight to moderate improvement from current state I'd be pretty happy.

An adjustable rear Iris will help (#2). Not sure what you are size you are using now. But try smaller. That would probably be most cost effective solution. An adjustable front iris is also helpful, but more for controlling line of white around bull. So, I didn't add it to previous recommendations.
Next, determining hyperfocal distance and Rx (#1 & #) would be next recommendation, but then cost will increase.
Tackling vision issues & irons is a never-ending challenge. It is both a rabbit hole and a moving target. It will never be perfect...especially after middle age, but you can make it tolerable.

 

[TuckerJ]

An adjustable rear Iris will help (#2). Not sure what you are size you are using now. But try smaller. That would probably be most cost effective solution. An adjustable front iris is also helpful, but more for controlling line of white around bull. So, I didn't add it to previous recommendations.
Next, determining hyperfocal distance and Rx (#1 & #) would be next recommendation, but then cost will increase.
Tackling vision issues & irons is a never-ending challenge. It is both a rabbit hole and a moving target. It will never be perfect...especially after middle age, but you can make it tolerable.

Your last thoughts probably sum it up. I've had glasses since I was 6 years old but when I was shooting open sights as a kid I never even considered focus. Seems like I could see everything fine.

These days I can tell these iron sights are far superior to open sights but my eyes are giving more of a challenge than they used to. Not impossible, but will take a little more work to feel like the system is working well.

I'm not sure what the aperture size of my Redfield sights is. Seems I read most from the factory were probably around 1.1mm?
I do have a handful of front inserts that let me play with the front aperture size. I've messed with them a little and have mostly tried the 3 biggest mm inserts I have. I think I've used the 2nd largest the most but might try seeing if going to the largest to get more white around the bull helps see things a little better and remove some of the target haze.
I'll at a minimum get a 510 sight with basic adjustable iris. I suppose I could get a 530 and the adapter to essentialy turn it into a 510 if the magnification makes things worse.

 

[Tim Slater]

Regarding foresight size, it's the brightness of the gap around the target that's critical rather than the size of the gap. Our brains can "see" light better than distance; if the foresight is off centre the gap is brighter on one side.

Modern thinking is to have a decent gap around inside the aperture; bigger = brighter. And there's less chance of overlapping the target. When the foresight is a very tight fit, less movement us needed to overlap, and this is harder to spot; the inner edge of the aperture isn't sharp, but blurred.

For me shooting prone, a 3.6mm aperture is the minimum on the 50m ISSF target, at a 33in sight base, and 3.8-4.0mm is more comfortable. A thicker foresight ring demands a slightly larger aperture, and a thin ring can go a touch smaller. Currently I think I have a thick-ringed 5.0mm on a 40in sight base.

Back onto the topic of focus, as described above. You can't focus at two distances at once; the rearsight aperture extends your depth of focus, so the target isn't totally blurred, but often it's not enough. A lens (distance + a bit to hit the hyperfocal distance) or lens system (ie a dioptre eyepiece) would work.

Just a small pedantic point, a Gehmann 510 is not a sight. It is a variable aperture eyepiece, or iris eyepiece. The sight is the part that adjusts for elevation and azimuth.