Rear sight 0.8-1.8

[NickyT]

Hi,
I've got a brand new rear iris sight for my FWB 800. MEC twin 0.8/1.8.
I'm always used the original but now, with the new one, I've the impression that nothing has really changed.
I mean that by varying the iris aperture I do not perceive a real improvement on the target (10 mt).
It almost seems that the image is less sharp. Is it normal or it's just a wrong feeling with the new sight?
Thanks for your support.

[Tim S]

Nick,

An adjustable rear aperture is used to maintain a comfortable brightness in your sight picture; from a typical standard of 1.1 or 1.2mm you could enlarge the aperture on a dark range. An adjustable aperture doesn't really affect the sharpness, assuming you mean the clarity and sharpness of the foresight (and target). Decreasing the aperture a lot will marginally improve your depth of focus, but usually makes the sight picture too dark.

Increasing your eye relief (moving the sight away from your eye) can also improve depth of focus. But, this restricts how much you see around the foresight.

If you need a sharper sight picture, see an optician for a lens. Typically your distance prescription +0.5 dioptres gives a good sight picture.

[NickyT]

thanks Tim, yes you are right. I'm near to 50, and my eyesight begins to weaken...

[tenring]

An adjustable iris works the same way as on a camera. It affects depth of field. The smaller the hole the most DOF, the larger the less DOF. As you age your eye loses its ability to focus near and far. The adjustable iris will help you get a little better sharpness either near or far but not both. That is still limited by “your” eyes ability to focus. Next time you are out adjust it just to get the most sharpness on the front aperture and take what you get on the bull. Then try it getting the best sharpness on the bull and take what you get on the front aperture. I believe most people like seeing the front aperture best and accepting a fuzzy bull. In any case it’s all subtle.

Hope that helps.

Chad

[Tim S]

An adjustable iris works the same way as on a camera. It affects depth of field. The smaller the hole the most DOF, the larger the less DOF. As you age your eye loses its ability to focus near and far. The adjustable iris will help you get a little better sharpness either near or far but not both. That is still limited by “your” eyes ability to focus. Next time you are out adjust it just to get the most sharpness on the front aperture and take what you get on the bull. Then try it getting the best sharpness on the bull and take what you get on the front aperture. I believe most people like seeing the front aperture best and accepting a fuzzy bull. In any case it’s all subtle.

Hope that helps.

Chad

A lens prescribed for shooting (i.e. distance +0.50) is a better way to achieve focal length that cranking down the aperture. A really small aperture makes for a dark sight picture which can strain the eye.