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Old April 25, 2018, 02:46 PM   #6
Join Date: March 4, 2005
Location: Ohio
Posts: 18,080
The trick is getting the focal length where it needs to be. If you don't want to invest in Olympic style rifle eyeglass frames (see, why Olympic sharpshooters look like cyborgs) and a custom-made prescription lens, the next best things are usually computer glasses and the like. Mine are at 1 diopter and work for pistol shooting. For young eyes, as little as 0.5 diopter works, but either way, you want to measure the distance from your eyeball to the front sight, divide the inches by 39.37 to convert them to meters, then divide the result into 1 to get the maximum diopter. Divide that last result by 2 to get a minimum diopter. That's the range you want to be in.

Example: You get into position with your rifle while your supportive spouse uses a tape measure to get the distance from your eye to the front sight without poking you too hard in the eye (to get even with you for imposing the inconvenience of the exercise). A trick here is to close your eye and allow the poke. Suppose the resulting measurement is 35 inches.

35 inches / 39.37 inches/meter = 0.889 meters

1 diopter/meter / 0.889 meters = 1.125 diopter

1.125 diopter / 2 = .5624 diopter.

So, rounding to practical values, you will want something between 0.56-1.1 diopters, depending on your eyes. That number would be in addition to your normal prescription for distance vision if you don't wear contacts or other correction before using this correction.

If you have good vision or if you wear contacts that correct your vision to normal, you will find a pair of reading glasses may do all you need. In the above example, you could buy a pair that is +0.75 and another that is +1.00 and see which one does better on the front sight at the range.

Part of the advantage of the snazzy Olympic style frames is you can adjust the lens height and position and axis angle to center the lens over and on a plane perpendicular to line of sight, regardless of the angle you are looking at the sights with. For many persons, especially in prone position, conventional glasses need a lot of nose pads or to be worn upside down to raise them to where the top of the frame doesn't interfere with your line of sight. This isn't as good as the custom frames and lens, but it's certainly an awful lot cheaper for just trying things out.
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