eye sight correction

[pcw]

I am near sighted and have astigmatism. I currently play at biathlon wearing contacts with my aiming eye having a +.5 diopter correction ( I believe that's correct). The front sight is wonderfully clear, too clear, and as expected the target is quite fuzzy and the "check gap" is not well defined. At times my contacts don't settle well and the astigmatism is very pronounced. I have been rereading the extensive section on aiming in Air Rifle Training and I have also followed many threads here on aiming. From what I can tell, the best solution is a lens and from what I've read here it seems that a lens can be applied directly to the rear sight. However, in spite of my searches, I can't find any info about how this works. I am also interested if anyone has alterative solutions to my eyesight problem. Just to be clear this is for biathlon, shooting glasses won't work. Regular prescription glasses would get too smeared with sweat and snow to see through.

[Martin H]

You need a Anschutz Monoframe. It attaches to the rear sight and holds a 25mm lens.
https://ahg.anschuetz-sport.com/index.p ... duktID=419

Sounds like you need to re-visit your lens prescription if the target is that blurry. But having a stable lens might just be the help your vision needs.
Cheers Martin

[Tim S]

PCW,

Where did you get your +.5 lens? Was it prescribed by an optician?

A + .5 lens gives a focal length of 2 metres. This gives a comfortable sight picture for many shooters (with a typical 26-28in match barrel). 2 metres is ahead of the foresight, the hyperfocal distance in technical speak; practically, thus means the foresight is still clear and the target is less blurry than if the lens is focused directly on the foresight.

However, that +.5 is normally added to your distance prescription. Say your distance prescription is -1.0; your shooting a prescription would be -0.5 (-1.0 + 0.5 = -0.5). Just a +.5 lens is perfect if your prescription is 0, no correction. If you are short sighted +.5 might be too strong; from your description, that sounds possible.

The astigmatism may be a factor too. Do your contacts correct for this? If not, are you mistaking the distortion for blur? If the contacts do correct for astigmatism, are these slipping on your eye?

EDIT: if I've misunderstood, and you mean your prescription is -0.5, in theory that's optimum for a Match rifle; no distance correction needed. However if the target is too blurred, yes a lens could help to define it a bit. Your Biathlon rifle may be a bit shoter than a Prone/3P, and this affects the lens you need.Remember the target should not be in sharp focus; the target is stable, but the rifle wobbles, so watch the rifle! US service rifle shooters seem to use +.75 (similar to pistol) which may suit you; -0.5 + .75 = +0.25.

[pcw]

Thanks Martin, that's the kind of thing I was thinking of. Would it be robust enough for biathlon is now the question.

Tim, a +0.5 correction was discussed during a visit to my optometrist, but there were limits to the correction based on what is available as a contact. I'm not completely sure that it is +0.5. So I think you are correct in that there is too much magnification. The contacts are intended to correct for the astigmatism, but often they don't settle well on my eyes, float around a bit and at those times the astigmatism is quite pronounced. Needless to say I am not getting a consistent sight picture. If I can move away from the contacts, I could wear my normal glasses while sking, remove them for shooting and have the lens provide the needed correction.

Thanks for your thoughts, pcw

[rpm]

Have you looked into the Gehmann Iris with 0x Diopter with correction. It allows you to correct your vision and improve your target image by reducing the iris. It has changed my whole shooting life.

[Tim S]

Have you looked into the Gehmann Iris with 0x Diopter with correction. It allows you to correct your vision and improve your target image by reducing the iris. It has changed my whole shooting life.

That's not really the best way to use a combined lens system + iris eyepiece (aka "diopter" or "optik"). The lens and the iris have two separate functions. Reducing the diameter of the aperture can sharpen your sight picture (that's what an aperture does anyway), but take it down too much, and the sight picture becomes too dark and strains your eye. Anecdotally a very small aperture will be more sensitive to head/eye position. Instead it's better to use the iris to control the relative brightness. Use the lenses to tweak your focal length for the desired balance of sharpness/blurriness of the foresight and target.

Also is the non-magnifying dioptre legal for Biathlon? It's not ISSF legal as there are two lenses; the rules allow one.

[rpm]

Thank you, you understand this far better than I ever will. At my age vision is a major problem. The Gehmann unit has helped me improve my sight picture and allowed me to enjoy shooting again. It’s not perfect and I suffer from eye fatigue mostly in prone.

I shoot 10m air rifle in my basement range and I have tried several lens without much success. The unit has made a difference.

Best of luck,

[pcw]

RPM, I've seen the Gehmann irises in the Champions Choice catalog, but I don't really understand them. I see that you can get diopter correction with or without magnification, but I don't know what that means. My understanding is that a diopter is a unit of measurement, how does that get corrected? There is also some huge iris that is supposed to correct for astigmatism, so I guess that is not what diopter correction.

[Tim S]

RPM, I've seen the Gehmann irises in the Champions Choice catalog, but I don't really understand them. I see that you can get diopter correction with or without magnification, but I don't know what that means. My understanding is that a diopter is a unit of measurement, how does that get corrected? There is also some huge iris that is supposed to correct for astigmatism, so I guess that is not what diopter correction.

PCW,

dioptres are what your lens prescription is measured in: ie -2.0 or +.75. A dioptre eyepiece has two lenses, that can change from about -4.5 (fairly short sighted) to +4.5 (fairly long sighted). Traditionally the two lenses magnified the image, effectively forming a 1.5X telescope. More recently Gehmann created a non-magnifying version.

There is indeed a huge iris that offers cylindrical correction for astigmatism. I think this is measured in degrees. The lens has to be distorted to match the angle of the astigmatism. No idea how Gehmann do this; an optician has the lens ground asymmetrically.

[pcw]

I think I’m starting to understand the idea. The one lens adjusts the focal point, while the other provides the magnification? I’m guessing that the lenses work in tandem for each change in focal point.

[Tim S]

I think I’m starting to understand the idea. The one lens adjusts the focal point, while the other provides the magnification? I’m guessing that the lenses work in tandem for each change in focal point.

Roughly; think of a very small telescope. The magnifying effect is small, although helpful to some shooters.

If you are shooting shooting in competition, do check the rulebook first. Dioptre eyepieces are not allowed in ISSF matches, even the non-magnifying one; for years the rules forbade lenses attached to the rifle, and since 2017 have allowed a single lens.