H Environs , its part of the rifle , it does screw into the receiver at five points , but i thinks its specificly made for the Challenger model. A freind of mine got one from Target Rifles South Australia thats similar but not the same for a Anschutz round action. There is a New member on this site Jeff and i think he might have them in stock , he sold me one for my Square action Annie. He is the guy that does the Tuner stocks. Cheers Ron

Ron, the sight that I use is very similar to this unit from Centra http://www.edinkillie.co.uk/ecatalog/centra-iris-aperture-18-competition-p-152.html?cPath=44_45 and as the specs say it has 2 discs of filters plus polariser of which I have only used the grey and the polariser in anger. I have tried some of the others but didn't really like them at the time so was probably a waste of money getting one with so many filters - ho-hum. Probably all that is required is this unit http://www.edinkillie.co.uk/ecatalog/centra-iris-aperture-30-combi-p-148.html?cPath=44_45 or this unit http://www.edinkillie.co.uk/ecatalog/centra-iris-aperture-30-pol-p-147.html?cPath=44_45 without the coloured filters. For the most part it would appear that the polariser is built in to the rear sight Iris and there doesn't appear to be swappable discs as can be got for the coloured filters
You will have noticed that I have avoided using the Centra UK web sight as its pretty useless a giving details of what you are looking for.

Hi Grumpy , once again thanks for the info mate. I just did some research on my iris which is the AHG 9781-s, which low and behold has a polarising filter inbuilt. Now if i can just work out how to use this bloody thing ? I bought this iris off ebay about 3mths back and still learnning what does what. I usually have it set on 2.0 and thats it no color filters unless its very overcast or foggy. Il have a play with it when we get back to shooting now in the New Year. It just so happens when im on holidays itching for a shoot all the ranges seem to close down until im due back at work. Its enough to give the man the shits ! Cheers Ron

Ron, 2 sounds awfully large, I usually have mine set on 1.0 thru 1.2 but noarmally closer to 1.0.
The Anschutz fixed irises are usually either 1.1 or 1.2, 1.2 being the more common of the two.
To find a start point try shooting a number of groups (5 shots should be good enough) at your usual target, that is a few groups on each sight setting. Start at say 1.5 and get smaller each time, noting the group size. You should see the groups get smaller with each setting until eventually they will start to open up again, at the point where the groups are their smallest is where you should be setting your rear sight. you probably won't feel that it is right and it may seem a little dark but it should work for you. Be sure to keep your eye at a constant distance from the rear sight, somewhere between 50mm and 75mm - whatever you feel comfortable with but don't crowd the sight. Altering the distance from your eye to the sight has the same effect as altering the size of the iris. Understand that the iris is essentially a focusing device and you should get best clarity (focus) on you forsight. With practice you will learn to judge where the best setting for the conditions you are shooting in is.

Now for the Polariser, with mine I can move it to the first click or detent, or all the way. As I said I'm not an expert on these things but I guess you would be looking for the sharpest sight picture particularly on the target. When there is no wind I understand that mirrage tends to make the target appear higher than it actually is so you shots print high, this because the light is being refracted through the different densities of air as it rises, caused by the uneven heating of the air, and the light from the image (target) you are looking at becomes scattered in the process making it look blurred. The polariser tends to block out the scattered light, just like trying to look into water with all those reflections and then put on a set of polaroid sunnys and hey presto, you can see whats actually in the water, the effecs of the scattered light which makes up the reflections is overcome by the polarising effect of the sunnys. As I said I am no expert and that is my understanding of things.

Hope this helps and good luck with you testing.

Hi Grumpy , Thanks for the tips, il be sure to try them out. I use to shoot with it closed up to about 1 to 1.5 i guess i must have opened it up to allow more light in as my practice is done usually on wednesday nights and the firing point is dark and gloomy. Maybe this wasnt the best thing to do so il take your advise and shoot groups and close it up again till im happy with it. Thanks for explainning in words i could understand about the polariser also. Sometimes when i talk with one of my mates he goes into what i like to call engineering language and after about 5mins he has lost me. Thanks again Cheers Ron

No Worries Ron, I try my best to help those who show interest. I think you have guessed that it is probably a mistake to open the rear sight to let more light through in low light conditions but sometimes it is just unavoidable. Its probably better to open the foresight to let more light through for the target, but thats not without its perils too and the effect can be the same as opening your rear sight but not so pronounced cause its easier to center a larger ring on a small dot, or in my case sometimes, a small splodge.