TargetTalk

Hi I was wondering wether someone could explain in layman terms the different strenghts in lenses? I have twenty twenty vision, do I need a lens of a certain strength? I'm in the midst of deciding which brand of shooting glasses to buy, but I want to get the whole story clear before I proceed and do so! Thanks for any advice you can give this newcomer!!

normal vision focuses at infinity with relaxed muscles.

tensing the eye muscles pulls the focus in closer

the range to which you can pull you focus in, is called accomodation. The more flexible the eye lens and eye muscles, the more accomodation

someone very young can focus on their own eyelashes. (I might be exageratting)

about the time you get to be 40 or so your eye lens and muscles get so stiff you no longer have enough accomodation to focus on the book your are trying to read. So you get reading glasses, or large print and hold it further away, until your arms get too short.

We are always told to focus on the front sight.

When your eyes get so stiff with age that you can no longer focus on the front sight (especially with the distraction of the target in the distance) then a helpful trick is to de-correct the vision, so that relaxed-muscle focus is no longer at infinity, but rather somewhat closer. (although perhaps not at the front sight, so that some eye muscle tension is used to focus).

A unit of power of a corrective lens is a "diopter". Starting with vision that is focused at infinity, +1 diopter of correction, will bring the relaxed focus in to 1 meter, you'll see better up close but won't be able to see distance any more. +2 diopter to 1/2 meter, etc. +10 diopter to 10cm. Drug-store reading glasses are positive numbers from about +1.25 to about +3.5. Lenses with a negative number are for near-sighted eyes to focus to infinity.

If you look in the shooting catalogs, you will see lenses at +0.5, +0.75 and +1 diopter, these will bring the relaxed focus in to somewhat in front of the front sight, and the eye muscles won't have to work as hard to focus on the front sight. Many people will try different strengths of lenses and pick the one that works best on that day with that light etc.

There are lens frames that look like bizaar glasses (knobloch, champion and others) that allow the mounting of such a lens or a corrective lens (often offset from the full prescription). They also allow the mounting of a blinder for the unused eye. An iris style aperture, color filters etc. There are ISSF rules on blinder size.

Eye protection is another reason for wearing glasses of some form.

Hope this helps

Poole
http://arizona.rifleshooting.com/

Thanks ! that cleared it all up. Seeing as I'm still on the youger side of stiff eye muscles I will just go on concentrating on the front sight through a non prescription lens until it becomes time to do so.