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Thread: Is this iris useful?

  1. #1
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    Is this iris useful?

    Now the FWB601 has gone and the endless agonising days to wait for my new LG400 to arrive form the sop, I'm turning my thoughts to a new iris.

    Up until now I have been using my basic Gehmann 510. It has served me well in bell target due to the varying amounts of light we have to deal with.

    Being as the new Walther is a very high end rifle, I have been looking at 'full on' Gehmann iris, this one 'seems' to have all the toys :-

    https://www.intershoot.co.uk/acatalo...Seller-31.html

    I know the hole size is useful, but are the colour filters and twin polarisers? What exactly is a polariser? I did ask a team member if the colours are useful in bell target and he said they very much are due to the varying glair from the lit target face.

    The rifle maybe over kill for bell target, so why not go overkill on the iris

    Any thoughts?
    Last edited by MrChipShoulder; 18-03-2019 at 12:15 AM.
    S400 MPR FT (walnut stock), TX200MkIII, CP88, STEYR EVO 10, Rapid MkI, FWB 300SU.
    http://www.airgunbbs.com/showthread....-range-project

  2. #2
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    MrChipShoulder,

    The idea is to obtain best contrast for your aiming, and to get the light intensity correct for you.

    The 'theoretical correct' aperture is apparently ca. 1.2 mm.

    'Modern' thought is to leave the aperture at its optimum value (1.2 mm), and to adjust light intensity solely by the use of filters in the rear sight and/or in the foresight tunnel.

    WRT the rear sight, the filters can be in the aperture unit, and/or in the glare tube out front of the sight if fited.

    The twin polarisers will allow you to adjust the light from ca. 60% (polarisers in phase) to zero (polarisers are crossed).

    This is mostly useful for use with the modern Sius etc. targets, which are very brightly illuminated, though can be useful on very bright days outdoors.

    For me, filter colours such as yellow & vermillion are best used outdoors.

    Have fun

    Best regards

    Russ

  3. #3
    Join Date
    Jun 2009
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    Taunton
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    In a word no, it's not ideal for 10m air IMO.

    Polariser do reduce glare, but I'd be surprised if you need one indoors. Smallbore and full-bore shooters use these in very bright sunlight. But indoors you'll just darken your sight picture.

    Colour filters are more useful, to enhance the contrast between the target and background. Yellow is ideal for artificial light as it cuts out UV, and blocks less visible light than other colours. I like yellow enough that I have a yellow prescription lens, as this is easy to keep clean.

  4. #4
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    Iris

    I agree with Tim, in fact, I'd be even stronger!

    Indoors, for air, a basic 0.8 to 1.8 iris is all you need, any thing else is an unnecessary complication.

    "Most of the kit in a fishing tackle shop is to catch fishermen not fish", a lot of shooting kit is the same!

    I know a lot of top class shooters, who even in out door full and small bore, who see any thing other than a basic iris as some thing else to get wrong or complicate a simple operation, and I'm married to one of them, her philosophy is KISS, "Keep It Simple Stupid."

    If you want to spend your money though, our favourite iris is the Centra Crystal, small, and great light gathering.

    Have Fun
    Robin
    Walther KK300 Alutec - Barnard 7.62 mm in Dolphin stock & now also with a .223 "Wilde" action, (but with Walther grip and wood!). - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?

  5. #5
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    As said above I would not bother with the polarisers but I would suggest you consider the filters as these can increase contrast and there is always the option of not using one as they normally have a clear/ straight through hole option. Itís better to have it and not need it than need it and not have it.
    ATB
    James

  6. #6
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    Thank you for the replies

    I have two problems I have to work around for my bell target shooting. One is how bright the lit target is, it can vary quite a bit, as a team we shoot on about 10 different targets (maybe more), all differing internal light and with differing lighting in the rooms as well. The other problem I'm still trying to work around is the white or black backgrounds they use.

    My own team use a target with a white background and that s fine as the outer ring of light in the sight picture is fine on the white background. But quite a few others use a black backgrounds including my 10M target club. I really struggle on the black backgrounds as the outer ring of what should be white light is not there , so you only get the inner sight picture with the black target dot.

    The way I've dealt with the black bell target background thus far is to wind rear iris all the way to the smallest aperture. When like this, as luck would have it, the iris is the same size as the fore sight so that when the sights are perfectly lined up, you only see the centre. If the sights are not lined up, you get portion of light breaking through, so you know that when there is no outer light, the sight is lined up correctly. I'm sure this can't be right, but it's the only thing I've found so far that kinda works.

    The problem is even worse at my 10m club as the whole target back stop is black with all sorts of deflection plates and rubbish around each target card. The outer ring of light in the sight picture is all broken up with differing shades of blacks and greys. Personally I'd say this situation is unshootable as I can't use my smallest iris trick as there is no light around the card to brake through, it's just blacks and shadows.

    I have got around the above situation with my daughters comp cards at the 10m club by making a removable white cloth background for her. Once the white sheet is behind the target, the problem goes away and she can get a normal outer ring of light in the sight.

    In the case of the bell target, I could simply open the iris right up to get a very large outer ring, but then I'm looking at all sorts of lighting and shadows, plus the inner dot can get fuzzy (due to too much light I assume?) and it would be hard to centre accurately. At the 10m club, you cannot do anything as the whole backstop is black regardless.

    I have been thinking one fix for the bell target would be a much smaller fore sight tunnel, maybe 10mm rather than the standard 18mm? This would stop the fore sight taking up all of the lit target aperture and then allow the outer light ring to brake through, thus giving a 'standard' sight picture??? Or perhaps one of these with a custom made smaller outer ring to close the outer black ring (I can make then with no problems).

    https://ibb.co/7nXMnzz

    Here is a picture I took a few weeks ago of the black faced bell targets I shoot on at comps.

    https://ibb.co/W32VkLB

    Here is a picture of our 10m clubs black backstop.

    https://ibb.co/kab77q

    Any thoughts would be very much appreciated as I have no idea what is best or expected?

    Sorry for the long post.
    S400 MPR FT (walnut stock), TX200MkIII, CP88, STEYR EVO 10, Rapid MkI, FWB 300SU.
    http://www.airgunbbs.com/showthread....-range-project

  7. #7
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    Taunton
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    That's an interesting fix. I'd make two suggestions.

    Don't open the iris to increase your field of view. You adjust that through your eye relief. The iris is there for adjusting the brightness of your sight picture; open it a little for darker ranges.

    A really small foresight tunnel will be dark. 10mm is really small. Even the old pre-war BSA/Parker-Hale tunnels were over 10mm internally.

    The backstop for 10m air shooting should be pale.

  8. #8
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    If you open the iris be aware that it will reduce your depth of field, you'll see the target blurred more in comparison to the foresight. It will give you more light though. Can't have both, and the opposite is true if you stop the iris down.

    Polarisers don't work indoors because incadescent light isn't polarised. Outdoors they reduce glare because the sun sends out polarised light.

    As robin says a 1-1.8 iris should do the trick. A yellow filter is about the only useful additions I can think of.

  9. #9
    Join Date
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    S400 MPR FT (walnut stock), TX200MkIII, CP88, STEYR EVO 10, Rapid MkI, FWB 300SU.
    http://www.airgunbbs.com/showthread....-range-project

  10. #10
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    Jul 2015
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    Hastings
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    MrChipShoulder,

    For me, I would have :

    #1 Centra 1.8 Crystal https://www.intershoot.co.uk/acatalo...-Iris-431.html

    #2 Centra 1.8 Basic https://www.intershoot.co.uk/acatalo...-Iris-644.html

    I doubt whether you would ever need an aperture greater than 1.8 mm.

    Have fun

    Best regards

    Russ

  11. #11
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    I'll go for the Centra 1.8 Crystal, thanks,

    What made you chose the Centra basic over the Gehmann basic iris just out of interest?
    S400 MPR FT (walnut stock), TX200MkIII, CP88, STEYR EVO 10, Rapid MkI, FWB 300SU.
    http://www.airgunbbs.com/showthread....-range-project

  12. #12
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    Hastings
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    MrChipShoulder,

    The Gehmann Basic (Anschutz Basic 9775 is the same iris, made by Gehmann) gives range 0.5 --> 3 mm - I do not need an aperture to open so large.

    The Centra Basic 1.8 gives range 0.5 --> 1.8 mm, which is the range I most need for target shooting.

    I do have the Anschutz Basic 9775 on two (2) of my field rifles, as I sometimes need to use a very large aperture when conditions are gloomy - my field rifles are fitted with 3mm front posts.

    Have fun

    Best regards

    Russ

  13. #13
    Join Date
    Dec 2012
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    Thank you Russ, the Centra 1.8 Crystal was ordered yesterday with the rifle
    S400 MPR FT (walnut stock), TX200MkIII, CP88, STEYR EVO 10, Rapid MkI, FWB 300SU.
    http://www.airgunbbs.com/showthread....-range-project

  14. #14
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    Dec 2012
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    Newport, South Wales
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    Hi,

    The Centra 1,8 Crystal is here now but I can't really see the difference between the Gehmann 0.5-3 iris and this Centra 1,8 Crystal. In my mind I think the Centra 1,8 Crystal is brighter at the smallest setting compared to the Gehmann, but is that just in my mind? Also the Centra is very small so my iris cup no longer fits.

    Am I missing something, or is the Centra just very expensive and very small?
    S400 MPR FT (walnut stock), TX200MkIII, CP88, STEYR EVO 10, Rapid MkI, FWB 300SU.
    http://www.airgunbbs.com/showthread....-range-project

  15. #15
    Join Date
    Jun 2009
    Location
    Taunton
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    To a degree a hole is a hole...

    The advantage of the Centra Crystal is its size. Small means that you can see more of the range around the sight. In recent years there is a thought that this can help with natural alignment, as you settle your head. For 50m Smallbore a small iris lets you see more windflags.

    Eyecups, chuck 'em away. I always found these came loose and blocked the aperture.

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