New member here, and I can solve your problems.
I am an engineer, studied optics some, I am a highpower shooter, and a photography enthusiast, so I know lens equations, I know shooters needs, and I make custom lenses. I can make astigmatic lenses. Turnaround time is usually under a week. My lenses are $40 delivered, and 23mm Knobloch is no problem - I cut them on a lathe, so I can actually do any diameter you want, down to about 3/16". All my lenses are impact resistant polycarbonate, and are Anti-Reflective coated.
I spec lenses based on math and photography formulas, calculated using your actual sight radius. None of this try 3 lenses and send 2 back nonsense.
So, with that introduction, here is how optical physics works:
KennyB hit the nail on the head. You do want to focus beyond the front sight. Most shooters and eye docs don't get this, and prescribe wrong because of it.
Any lens/aperture system (ie your eye and pupil) have a natural depth of field. If that depth of field is small, you are kind of screwed, because you can focus on either the target or the sight, but not both. However, if you make that depth of field big, and you adjust your focus so the depth of field is centered between your sights and the target, you can actually create a situation where the target and the sights are is sharp focus at the same time, because the sights are at the near edge of the depth of field at the same time as the target is at the far edge of the depth of field. You see photographers doing this all the time - a pretty girl is in sharp focus, and the mountains behind her are in sharp focus as well. The way this is done requires two things: using a small aperture to create a big depth of field, and adjusting the lens in your camera to balance your depth of field between the girl and the mountain.
So, let's address focus first. Where do you want to focus? To split your depth of field between two objects requires some math which I will not go into here, but when one of the objects is effectively at optical infinity, as your target is, the math simplifies. TO split your focus between a near object and infinity you want to focus at 2x the distance to the near object. This is called your hyperfocal distance. So, aim your pistol, have a laboratory assistant take out a ruler, and without poking you in the eye, measure the distance from your eye to the rear sight.
Example: let's pretend that distance is 24". Your hyperfocal distance that you want to focus at would be 48".
Next question is how you do that. The relaxed eye focuses at infinity, and to focus up close you have to exert the eye muscle, the cilary. Natural point of aim principles say that you would rather not exert a muscle, and further, as you get old and presbiopic you might not be able to pull your focus back to 48", and especially not to hold it there for a minute as you aim and shoot. So, the other way to move your focal point is to add a lens, which shifts your focus while leaving your eye muscle relaxed. How much lens? Lens power in diopter is simply the inverse of a lens focal length, in metric. A 2 diopter lens will focus you at 1/2 meter. A 3 diopter focuses you at 1/3 meter, etc.
So, if your hyperfocal distance is 48", convert this to metric, that is 1.22 meters. THe lens you would want is the inverse of 1.22, or 1/1.22 = 0.82. You would want a 0.82 diopter lens. Lenses actually come in 0.25 steps, and you always want to round down (I won't go into why here), so 0.82 becomes 0.75 diopters is your shooting lens if you do not wear glasses for distance vision correction.
Now, if you cannot see distance clearly, but need distance glasses (reading glasses do not count), and/or if you have an astigmatism, what you need to do is see an eye doc, and get a distance vision correction. You would then take that prescription, and add the +0.75 to the first (spherical) number, and that revised prescription is your ideal shooting lens.
That gets your focus centralized. Next step is making your depth of field as big as possible. To do this, you want a small aperture. In cameras, apertures are adjustable, so the photographer simply sets it. In your eye, the pupil is the aperture, and it varies with light, and it also has a minimum size of around 1/8". You can decrease your aperture size further by using a peep sight. THe smaller you go, the better your depth of field and the better your focus. Minimum size is dictated by brightness - small apertures limit light coming through, so at some point the image dims.
Solution is to get a small aperture on your glasses. Again, I have just started experimenting with making self-adhesive apertures for lenses. With one of these, the front sight and the target will be in perfect simultaneous focus. I'll set you up with a set.
Please feel free to respond to
shootingsight@nuvox.net
or call me at 513-702-4879
if you want to discuss further, but I can make this work, and if you are trying out for the olympics, I will jump through hoops to get you what you need in the fastest possible timing.
Regards,
Art Neergaard
PS, first step you can take ASAP is to go to an optometrist and get measured. WalMart optometrist is fine, it'll probably cost $40 and take 15 minutes. With that prescription, I can do all the math necessary to get you the lens you need. I can mark the orientation for astigmatism, though usually I prefer to give you a special target to look at, and instructions on how to twist the lens till you see the focus get the best possible.