Rear Iris

[kbean]

I’m thinking about trying an adjustable iris on a centra rear sight.
It would be used for 50ft and maybe 50m smallbore 3P.
Any suggestions on which iris to try?

[Th.]

https://gehmann.com/en/Sighting-Equipme ... ht-Irises/

[Tim S]

I’m thinking about trying an adjustable iris on a centra rear sight.
It would be used for 50ft and maybe 50m smallbore 3P.
Any suggestions on which iris to try?

For mostly indoor shooting, look for something simple; both Gehmann and Centra make a iris eyepiece for a Centra sight*. If your budget allows, built-in colour filters are handy outdoors; click in a grey or polariser to tone down glare, or a yellow to make the target pop when it's overcast. But filters aren't essential for indoor shooting. Yellow will cut out glare from fluorescent lights, hut most other colours will darken the sight picture too much. Don't bother with polarisers for indoors, as these work on natural light.

[Frank in Fairfield]

I have rear iris on three air rifles.
I had one on my M16 and my Garand too.
I grew up with one on my Daisy Model 25 (I am 77 very soon).
The one on my FWB601 is a Gehman but someone had to tell me about it.
I have always ignored the rear iris regardless of the size as your eye will automatically find the center, regardless of the size of the hole.
A simple test is in order and all you need is a piece of electrical tape.
Tape over the iris and stick a pin in the hole.
Shoot..
Too small?
Use a thumb tac.
Larger?
A nail.
Try and shoot your best with each hole.
When you are finished you will have your answer.

[Tim S]

I have rear iris on three air rifles.
I had one on my M16 and my Garand too.
I grew up with one on my Daisy Model 25 (I am 77 very soon).
The one on my FWB601 is a Gehman but someone had to tell me about it.
I have always ignored the rear iris regardless of the size as your eye will automatically find the center, regardless of the size of the hole.
A simple test is in order and all you need is a piece of electrical tape.
Tape over the iris and stick a pin in the hole.
Shoot..
Too small?
Use a thumb tac.
Larger?
A nail.
Try and shoot your best with each hole.
When you are finished you will have your answer.

Frank,

Do you mean to say that your rifles have an aperture rearsight? An iris is an aperture, but one where the diameter is adjustable, like on a camera, or the human eye. Would the M16 and M1 not have a simple aperture?

The human brain (not the eye) is very good at recognising patterns, like concentric circles. But it won't automatically centre the eye and head behind the rearsight aperture. The small apertures used in target shooting may limit parallax error to a degree, but don't totally eliminate it. Sometimes, centring the eye is not physically possible due to the shape of the stock. I once coached a beginner who spent several sessions aiming through a gap in the side of the rearsight: spoiler, their groups were terrible.

There are much better and easier ways to use an iris than messing about with tape and sharp points. The iris is there to tweak the aperture to control how much light reaches your eye, compensating for a different range or changes in natural light. 10M and 50M target shooters typically want a fairly small aperture to increase their depth of field, allowing a clearer (but not totally clear) target. A nail hole would be ginormous. In contrast military apertures are often quite large, just to provide a quicker aim*.

After setting eye relief to get the desired space around the foresight tunnel**, close down the iris. Gradually open it until the sight picture is nice and bright, then back off a touch. With an eye relief of 1-3in, most shooters seem to want an aperture between 1.0 and 1.5mm depending on the conditions. Add a +.5 lens (on top of any distance prescription) so you don't rely totally on the aperture for focal length, and you may be able to use a slightly larger aperture.

*Not universally, as a target shooting element has often had the clout to dictate a very small aperture. Ans some designers just get things wrong.

**This forum is intended for Olympic style shooting, where a tunnel foresight dominates.

[Frank in Fairfield]

Yes aperture.
Two of my air rifles have the aforementioned front tunnel sights.
FWB601 and HW35.

Don’t preach to me about for what this forum is intended.
You can all kiss my rosey red ass!

[Tim S]

Yes aperture.
Two of my air rifles have the aforementioned front tunnel sights.
FWB601 and HW35.

Don’t preach to me about for what this forum is intended.
You can all kiss my rosey red ass!

Well perhaps folks are right who say growing old is inevitable, but growing up is optional. I'm sure we'll all remember your insightful comments.

My apologies to the OP, who wanted advice on purchasing an iris.

[m1963]

Well said, Tim S!

[rgibson]

Mr. Bean,
I use 2 Gehmann 510s. One on my Smallbore and one on my Palma rifle. They are simple and robust. I originally bought one for the Palma rifle that had polarizing filters and the recoil shook it apart. I like the KISS Principle. I know the SBR rifle would not beat the irises with colors and filters apart; just saying they are not as robust.
You are a Class Act, Tim S. HUZZAH!

[kbean]

Thanks for the help. I'm thinking I may try one of the Gehmanns without filters to start and see what we think about it.
I appreciate it!