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 Post subject: Rear iris questions
PostPosted: Sun Oct 15, 2017 12:43 pm 
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I'm looking to get my son a new rear iris for competitive smallbore. He shoots mostly 50ft indoor but also shoots 50yd and 50m outdoor.
Can someone give me the Cliff Notes version of what the color and polarization settings do? i'm assuming the polarization removes glare much like polarized sunglasses? Seems good for outdoor and bright indoor ranges. Is there a difference between the Centra/MEC, Gehmann and Anschutz irises besides cost?

Thanks for any and all replies and advice!


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 Post subject: Re: Rear iris questions
PostPosted: Sun Oct 15, 2017 1:20 pm 
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Location: Taunton, Somerset
Yep, polarisers cut down glare. Gehmann used to advertise polarisers as combating mirage, but that's hokum. I rarely use one, but I shoot outdoors mostly on a well shaded range.

Colour filters change the contrast between the aiming mark and the target background. This can be to tone down the background in bright light, or to make the mark stand out in overcast conditions. I use a yellow filter under most conditions as it cuts UV light, and doesn't darken the sight picture too much.

US Olympian Eric Uptagrafft gave a very good description on this forum of his use of filters to maintain a good and constant sight picture. If you search, I think it was 2011-ish.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Oct 15, 2017 3:40 pm 
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Keep it simple.. One of those things they will forget to adjust in the heat of battle. Id suggest apature size is most important followed by a handful of colors. If theres enough light my eyes prefer an amber color. Yellow seems to hurt. I guess thats why they make more than one color.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Oct 15, 2017 4:23 pm 
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Joined: Wed Apr 11, 2012 8:35 am
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Location: United States
Get a Gehman 510. Leave about 1.0-1.2 and forget about colors, polarization. Especially for a JR shooter. Keep it simple.


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 Post subject: Re: Rear iris questions
PostPosted: Thu Nov 02, 2017 4:07 pm 
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Joined: Wed Feb 07, 2007 11:29 am
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I absolutely second Morgen’s statement. KISS!

MarkTrew


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 Post subject: Re: Rear iris questions
PostPosted: Sat Jan 27, 2018 6:42 pm 
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Joined: Sun Oct 08, 2017 10:22 pm
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At risk of hijacking/resurrecting an old thread...
I recently picked up a 'new to me' rifle for my son, and he used it for the first time today. He complained that the sight picture was weird/dark/foggy/blurry (he's 9, so some interpretation is necessary). I tried adjusting the distance of the sight to his eye, but he said that didn't help. He's shooting on a poorly-lit indoor range at 50ft.

I pulled the rear aperture (non-adjustable) and it measures 1.0mm (as best I can judge without gauge pins).

So my first instinct is to pick up a basic adjustable rear aperture to see if getting more light will help. Is there any functional/quality difference between the Anschutz, Centra, and Gehmann to justify the price difference?

Any other suggestions for clearing up the site picture?

Is there an 'ideal' distance between the rear aperture and the shooter's eye?

Thanks,
mark


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 2:48 am 
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Location: Taunton, Somerset
Mark,

I'll start with eye relief. Normally this between 1in and 3in. The exact distance depends on sharpness and field of view: more eye relief gives a sharper sight picture, but it's darker, and there is less space around the foresight.

Regarding the rear aperture, 1mm isn't large and I don't think helps on a dark range. A larger aperture, say 1.2mm, would let in more light. Some shooters go larger in low light, but that's with a prescription lens for focal length. Increasing light on the range would be a benefit for everyone. In a dark range, your son's pupil is trying to expand to let in light, but that messes with his focus. Brighter ambient light makes the pupil tighten, which improves focus.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 3:36 am 
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Joined: Sun Sep 04, 2016 10:59 am
Posts: 550
Location: A new global Great Britain
marky-d wrote:

So my first instinct is to pick up a basic adjustable rear aperture to see if getting more light will help. Is there any functional/quality difference between the Anschutz, Centra, and Gehmann to justify the price difference?


A hole is a hole.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 6:26 am 
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Joined: Wed Feb 07, 2007 11:29 am
Posts: 127
The person stating a hole is a hole is doing a disservice to the 9 year old trying to learn to shoot, in my opinion. Concurring would be every entry earlier in the thread.

To provide some basic information might help in the formulation of a solution.

What front and rear sights were on the previous rifle that the 9 year old used? Were the front and rear aperture adjustable on the previous rifle? What was the hole size, front and back, on the previous rifle? What was approximate sight radius on the old rifle?

Can you answer the same questions for the new rifle?

What target is being used at 50’? This might seem to be a frivolous question to “a hole is a hole” but, as an example, a NRA A-17 Target has a bigger black than the USAS-50 target. So, if the front aperture is too small, “the hole” might be too small on the front sight.

With more data a better answer might occur. However, I agree, the rear aperture might be smaller than normal, specially for darker ranges.

MarkTrew


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 7:04 am 
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Location: Taunton, Somerset
MarkTrew wrote:
The person stating a hole is a hole is doing a disservice to the 9 year old trying to learn to shoot, in my opinion.
MarkTrew


Mark,

I think Peter meant that there was little to chose between an Anschutz, Centra, or Gehmann iris. Centra make Anschutz branded irises anyway.

I read no opinion on aperture size, rear or front, in Peter's response.

Foresight aperture size is very important for a reliable aim, but it doesn't normally affect the brightness or clarity of the whole sight picture. Rear aperture size, and ambient light certainly do.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 10:40 am 
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Posts: 17
Thanks guys. I do suspect that the range lighting is probably the easiest fix here, but I wasn't able to check to see if it could be adjusted. I'll give that a shot next time we're at the range.

I don't know the exact details of the previous rifle sights, but it was a Savage Mark I FVT (21" barrel). The sights were not adjustable, and the front used a metallic insert of unknown size.

The 'new' rifle is a 1970 Anschutz Modell 54 (26" barrel). The sights are not adjustable, and the front uses a "clear aperture" plastic insert with a 3.8mm diameter.

We are using the A-17 targets, but when I ask him about the front 'ring size', my son says it looks about the same as the Savage.

The funny thing is that despite the sight picture complaint, he still shot as well, or better, than with the Savage after he settled into it (after 7-8 bulls). But I am trying to encourage him to give me more feedback -- to make the rifle fit HIM, rather than forcing him to fit the rifle -- and so I want to be responsive to his comments.

Thanks again for the feedback. Unfortunately it's going to be a month before we can get back to the range, but I thought that would be a good time to buy and try out an adjustable iris.

marky-d


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 11:06 am 
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Posts: 1350
Location: Taunton, Somerset
Mark,

A 3.8mm is entirely suitable for a 26in Anschutz barrel prone. You'd want to go larger for standing/Kneeling so the bull stays inside the aperture, even with the larger wobble area.

When you say the rearsight is not adjustable, you do mean the eyepiece for aperture size? All Anschutz target rearsight are adjustable for elevation and windage, and eye relief. At 9yo your son may want the sight quite far back; older Anschutz sights with two retaining thumbscrews will hold steady with only one thumbscrew tight on the dovetail. This gives plenty of scope to fit. As an aside, at 9yo, I'm impressed that he can hold a Match 54. With the 26in barrel, that's a 10lb rifle.

Back to the rear aperture, a simple iris (no filters or doodads) isn't expensive, and will do no harm. Anschutz do make fixed-aperture eyepieces in varied sizes, so you could find a 1.2mm. With a spare eyepiece you could drill out the first to a larger size, if you want.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 3:22 pm 
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Joined: Sun Oct 08, 2017 10:22 pm
Posts: 17
Thanks Tim.

Yes, when I said "not adjustable", I was just referring to the iris/aperture sizes.
I've moved the rear sight back, such that the rearmost thumb screw is still on the receiver, but it's good to know that I could go further if I need to.

As far as the weight of the rifle, heh-heh, yeah, it's too heavy for him to hold right now, but so far he's just working on prone (supported), so it's okay. I thought finding one with a shortened stock would help (and it does to some degree), but the long heavy barrel combined with short arms is a tough situation. To support the rifle, his left hand is RIGHT in front of the trigger guard, which leaves a lot of weight cantilevered out front! I am hoping the heavy rifle will force him to develop good habits (i.e. support with bones, not muscles), but I may have over estimated a little....

marky-d


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 3:42 pm 
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Joined: Mon Jan 03, 2011 11:33 am
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Location: Taunton, Somerset
Mark,

Even with the stock cut down, it's hard for short arms to balance a 26in barrel. Adding weight to the butt would alter the point of balance, but makes the rifle too heavy.

Lopping a few inches off the barrel, would improve the balance (and overall weight), although some folks are leery of cutting the muzzle, as it's choked.

A Match 64 would be a better size.


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 Post subject: Re: Rear iris questions
PostPosted: Sun Jan 28, 2018 11:07 pm 
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Joined: Fri May 18, 2012 9:37 pm
Posts: 263
Location: Cincinnati, OH
Typically, filters are a waste. You want as small an aperture as you can, without the image starting to dim. To accomplish this, you want a variable aperture.

Filters cut out visible light, so if you have light to spare, my thought is that you should deal with it by reducing your aperture, so at least you get a depth of field benefit from reducing lighting, rather than just filtering out excess light. The single exception is a pale yellow, which will filter out UV. I have never found any scientific evidence as to why other colors of filter would help a target shooter, so while I do not discount personal preference, there is no rule as to what you should use. So given that pale yellow is the only one, and only if there is a lot of UV, I'd recommend a screw in pale yellow it you think you need it, but paying extra to get multi colored wheels in the sight is a waste.

Theoretically, a +0.50 diopter lens will remove strain from the eye muscle, but at 9 yrs old, with excellent accommodation, and smaller eyeballs than an adult, I would skip it, as the complexity of one more item likely outweighs the benefit.

Bottom line, get a variable aperture, don't bother with filters.

Polarization is also often a waste. When light strikes a surface and is reflected, it is polarized differently from direct light. So getting polarized lenses that are oriented to let direct light pass, and screen out reflected light can reduce glare off of water, or other cars windscreen, or even pavement. In shooting however, your sights are viewed in silhouette, so there is not really any reflective surface to be seen, and typically targets are matt, so there is not much reflection there. Occasionally, with a strong setting sun right behind you, you might get reflection off the ink of the bull, though I've never shot in those conditions.

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 Post subject: Re: Rear iris questions
PostPosted: Mon Jan 29, 2018 5:40 pm 
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Joined: Mon Mar 22, 2004 6:03 pm
Posts: 265
Location: ...ain't in Texas no more....
Gehman 510. Simple and does the job that it is needed for.....and simple for a jr shooter.
ken


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 Post subject: Re: Rear iris questions
PostPosted: Tue Jan 30, 2018 3:59 am 
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Location: A new global Great Britain
@Mark. I try not to do disservice to anyone.
The question was is there a functional difference between the 3 makes of basic iris mentioned. If they contained lenses or filters then optical resolution and distortion might be a factor. But they simply are variable holes, so there is nothing to choose between them optically.


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 Post subject: Re: Rear iris questions
PostPosted: Tue Feb 06, 2018 11:15 pm 
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Posts: 127
I stand corrected. I focused on the first sentence and ignored the second, regarding a “ hole is a hole “

Sorry.

I agree a simple adjustable rear iris may be of benefit, like the 510 Gehmann. Take a look to insure the front sight does have a generous ring of white around the bull.

MarkTrew


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 Post subject: Re: Rear iris questions
PostPosted: Wed Feb 07, 2018 7:43 am 
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Location: A new global Great Britain
No problem.
The rear iris size will have minimal impact on white round the bull. Need to change front aperture for that.
Rear aperture affects depth of focus and brightness mostly.


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 Post subject: Re: Rear iris questions
PostPosted: Fri Feb 09, 2018 1:54 am 
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Get a Gehman 510. Leave about 1.0-1.2 and forget about colors, polarization. Especially for a JR shooter. Keep it simple here


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