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The "right" pair of glasses can do wonders. BTDT.

I typically adjust my scopes for use with no glasses. I figure having my glasses on my face when I need the rifle for serious purposes is something I shouldn't count on. Same for binoculars.

An illuminated scope with a red dot in the center is a nice crisp red dot. Even with no glasses.

A red dot optic, such as an Aimpoint or a Lucid or others, is an ugly diagonal smear that runs from upper left to lower right in the image. I had tried wearing my reading glasses (hey, the optic is closer to my eye than a book I'd read) and that didn't work. The other day I'd accidently worn my driving glasses (clear things up from about 30 feet in front of the car to as far as I can see down the road) when I carried my stuff to the range.

When I got the AR15 with the Aimpoint out of the case, loaded it up and aimed at the target I was surprised to see the dot was about as clear and round as I would see on a computer screen/image.

I can get a pair of $10 to $12 glasses of the rack at Walmart that do the same thing for me. I checked. No need to risk my expensive glasses for shooting (I seem to drop stuff, lay things on other stuff, scratch the lenses, etc.)
 

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Discussion Starter · #22 ·
In January, I was pursuing the astig angle because multiple eye exams over two years yielded different prescriptions for my right eye. In March, I finally used my best corrective lens (for that day) while seeking optimal head/eye position, which improved my sight picture considerably: target and dot reticle were sharp, and parallax was close to 100 yards. It truly was a "Eureka" moment. I can't overstate how much effort I finally put into altering my cheek piece and head position to get a sharp sight picture.

As I have described in other threads, I can attach my round corrective lens to my scope's eyepiece. It is much better than trying to look thru the upper left corner of my right lens or trying to position my Knobloch lens in a good position.
 

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If you have an astigmatism, it means the cornea of your eye has a slight bulge, so the surface is shaped more like the surface of a football, rather than a basketball. So instead of having the same radius of curvature in all directions, you have a slightly smaller radius in one direction, and a slightly larger radius in the other. Conceptually, this is taking a sphere, and stretching it in one direction.

To correct this, you need a lens that is also football shaped.

This means there are two additional values that determine an astigmatism lens, versus a 'regular' lens. First is the degree of difference between the two radii of curvature, the other is the direction in which the lens is stretched.

When you are setting up your shooting lens, it is thus important to have the right power and also to orient the lens relative to your eye. Depending on the strength of your correction, it is also important to look through the lens in a perpendicular fashion, which can be difficult to do when shooting prone.

Attaching the lens to the back of the scope will fix the perpendicular issue, however as you tip the lens to form a cheek weld, the lens will not tip with you, so you need to account for the 10-20 degrees of head tilt when you orient the lens on your scope.

Bottom line, if you are having trouble with cheek rest to get good focus, try first just rotating the lens slightly to tune it while you are in the shooting position - that might clear up your image.
 
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