Shooting Glass Iris - how does it work?

[Furballxl6]

I have been using a pair of Knobloch glasses for pistol shooting with an adjustable iris to increase the depth of field. This obviously works, and although I cannot see both the target and the sights it is better than using nothing; however I hate using something that I do not understand. Can anyone tell me how reducing the aperture of the iris can increase the depth of field?

[20series]

My understanding is that it restricts the amount of light being let through which enables you to get a better focus on the foresight. On my Anschutz I use approx 1.1mm, however in differing light conditions this may change.

Alan

[Vic Thompson]

Long winded, and geared up to Photography, but it might help : http://en.wikipedia.org/wiki/Depth_of_field

Vic T

[RobF]

easy way to think about it...

if the aperture is wide, it can let in light from all angles that bounce off the subject, so you see a scattered (blurred) image if it's not focused right... but it's bright.

if the aperture is small, it only lets light in directly from the subject, mostly in straight lines, so the image is sharp, but because there's not a lot of scattered light, it's dark.

any help?

in low light you need to open the aperture, but that reduces the depth of field, so reducing the aperture too much to get a better depth of field in low light can tire your eyes too much. It's a trade off.

If you watch a cat, even when there's sufficient light, they eyes get wide when they are targeting before pouncing... this is because they are doing the opposite, they are opening their eyes to shallow the depth of field so that they can determine the distance accurately.

[Furballxl6]

Yes makes it much clearer, this is why you need to know - I will ensure that there is sufficient light to allow a smaller diameter iris.

p.s. are iris's permitted in competitive pistol shooting?

[RobinC]

Shooting glasses and iris's are permitted in ISSF 10 mt competitive pistol shooting. The principle is to get the sights sharp in focus particularly the foresight, the target will be blurred which is also advantagous as it stops your vision being drawn to the target, this is the most common fault that will cause a flyer. Just concentrate on the sight picture and area aim just below the blurred aiming mark.
For any one with other than perfect vision shooting glasses with a specific shooting prescription and an iris are a massive help for pistol shooting, and even with perfect 20/20 a lens and iris can help.
For the best guidance on shooting glasses, prescription lens's, and iris's look on www.knobloch-schiessbrillen.de and go to the sections called refraction and prospeckt. They have an English translation.
Best regards
Robin

[jonyb]

i can't remember the last time i saw a competitive pistol shooter,wether it be county,national or international level, using an iris.?
if they were the answer why are they not used.
i would say spend your money on the right prescriptive lens,and remember the foresight needs to be sharp and the target blurred. as mentioned in an earlier post;area aim.
it's easy to do but do not get hung up on all the shooting paraphinalia .
just practise and get some coaching if needed.