I normally shoot aperture sights with a correction factor of .5 added to my prescription for my right eye and have been fairly successful with that. Recently I wanted to try a fun match with an open sighted rifle and discovered that what I used before was not even close to anything that works. Then I tried my normal (trifocal) glasses skewed around so that I could see the sights through my bottom (reading) correction of +2.50 and both the rear leaf at 12.25 inches from my eye and the front post at 34 inches were both in focus but the bull at 50yds was pretty fuzzy.
Anybody have any better corrective lens ideas or do I give up this open sight idea?
Thanks, Mike
Question on open sight eyeglass lens correction
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ShootingSight
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Normally, a +0.50 correction for a long rifle, or a +0.75 correction for carbine/AR/pistol is the correct answer.
However, the assumption is that these corrections are added in additions to any corrections your eye needs to see infinity correctly (aka your 'distance' prescription). Eyes can change with time, so if you are working off a year old prescription, I'd say get yourself rechecked, and add the corrections to a recent prescription.
However, if you are seeing day to day variation, there are a few other factors to think about. Degree of hydration can influence focus. If your eye diameter swells or shrinks by 1/100th of an inch, it will throw your focus by 0.50 diopters, which is significant.
Also, the sugar level in your ocular fluid, which will follow blood sugar level with some time delay, will influence the index of refraction in your eye. I have not gone through the math to figure out what expected swings are, and how much it will drive your focus shift, but I recall that hyperglycemic attacks by diabetics involve blurred vision, so it can be a factor. If you don't eat all day during a match, that could contribute.
I'm an engineer, so I can calculate lens equations. I am not a doctor, so I do not understand all the underlying anatomical stuff. Keep hydrated, and keep your blood sugar at a reasonable level. But if you have continued bouts of focal shift, do talk to a doctor and let them know. Older overweight people are candidates for diabetes Type II, and you'd rather catch this stuff early than late.
However, the assumption is that these corrections are added in additions to any corrections your eye needs to see infinity correctly (aka your 'distance' prescription). Eyes can change with time, so if you are working off a year old prescription, I'd say get yourself rechecked, and add the corrections to a recent prescription.
However, if you are seeing day to day variation, there are a few other factors to think about. Degree of hydration can influence focus. If your eye diameter swells or shrinks by 1/100th of an inch, it will throw your focus by 0.50 diopters, which is significant.
Also, the sugar level in your ocular fluid, which will follow blood sugar level with some time delay, will influence the index of refraction in your eye. I have not gone through the math to figure out what expected swings are, and how much it will drive your focus shift, but I recall that hyperglycemic attacks by diabetics involve blurred vision, so it can be a factor. If you don't eat all day during a match, that could contribute.
I'm an engineer, so I can calculate lens equations. I am not a doctor, so I do not understand all the underlying anatomical stuff. Keep hydrated, and keep your blood sugar at a reasonable level. But if you have continued bouts of focal shift, do talk to a doctor and let them know. Older overweight people are candidates for diabetes Type II, and you'd rather catch this stuff early than late.
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Martin Catley
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Sighting
I think some are missing the point, you are needing more power to see the rear sight accurately if you have shooting Glasses can you try different powers to help?
With the "open" sight you will have to lose somewhere to see that rear accurately as well as the front, it will result in degradation of the Target to some extent and will need a lot of experamenting!
With the "open" sight you will have to lose somewhere to see that rear accurately as well as the front, it will result in degradation of the Target to some extent and will need a lot of experamenting!
Thanks, Martin, that was my feeling as well. I normally shoot aperture sights and have for 60+ years so "open" sights are a new experience. My Dad was a lifelong target shooter, so his kids got Redfield peeps on their kiddie rifle from the start. Heck, they were only about $4 back then.
Peeps put me into a class where I compete with guys (and gals) with telescopic sights.
Mike
Peeps put me into a class where I compete with guys (and gals) with telescopic sights.
Mike