Iron sights: Explanation of lenses?

[DRNewcomb]

I recently tried (as in held the rifle) a Rightsight from Stallings Machine that included a .5 diopter lens. I certainly noticed that I was able to see both the target and front aperture much better, even without my shooting glasses. I've been looking at the use of lenses in front sights and I'm a bit confused. As I recall, the Rightsight had the lens after the aperture. I thought that the idea was that for all us presbyopic shooters, that your shooting glasses had about a +.5 diopter correction, so that you could see the front aperture, then beyond that you would want a -.5 diopter correction to bring you back into distant vision.

Most of the lenses I see for various front sights are described as "magnifiers" that go in front of (before) the aperture. That does not seem to make sense to me. I think maybe I don't understand something. What I am trying to to is to find a lens I can try in my Tompkins sight before I decide to drop ~$400 on the Rightsight.

Can anyone provide (or point to) a good explanation of the use of lenses in front sights?

 

[NateG]

The lens is usually placed on the far side of the iris (so it's shooter's eye, rear sight, front iris, front lens, target)--but that doesn't really matter much with the iris and lens so close--but it does avoid having something between your and the iris that could get gunk on it.

The +.5 correction in your shooting glasses or rear sight brings the front sight into (more) relaxed focus. The +.5 lens in the front sight magnifies the target--at the expense of some additional blur. However, since you can close down the rear aperture, you can increase the depth of field and get back most (or all) of what you lost to the blur.

I usually run a rear aperture of about .7mm on an overcast day, .5-.6mm on a bright day. With the aperture that closed down, I can readily see the target rings at 300 yards--and they can be a bit distracting at 200 at times. Many people will open the rear aperture too much; in every day life, bright light usually means better vision since your pupil constricts and that acts like a pinhole camera. So, your brain thinks that a brighter image is a better one, so if only that sight picture could be brighter, I'd see better. However, the rear aperture is the pinhole camera. Closing it down gets the benefit--at least until you close it down too much. Getting as close to the aperture as possible without getting hit will allow you to close the aperture down more and still have the same amount of light hitting your eyeball.

Definitely get a lens for the sight you have... unless you also want the elevation adjustment and the adjustable aperture anyway. Then you'll have to find the size range you want. I prefer a wide open aperture, but there are lots of good shooters who use a small one.

 

[dblinden]

To add to the above.....

The plus diopter lens (likely a 0.5 in your Rightsight) magnifies the target black and the number board. it is not placed to change the visual image of the aperture itself. That is the reason you will need a much larger aperture opening when a front lens is used than without. If the lens was placed in front of the aperture, the magnification would then be proportional for the aperture and the images down range. However, the quality of the aperture image may be much degraded depending on your vision correction. Keep it in front where it belongs.

Dennis L

 

[Pres100]

There's not a lot of information that I could find on this subject and I struggled at first getting set up. I have the Stallings 30 mm Rightsight and mostly shot at 200 yds. I had to remove the .5 lens for 200 yds to get a good sight picture, but struggled With the aperture settings front and rear.
I recently shot a 1000 yd match and struggled some more until I realized I didn't have the front lens in. Without it I could barely see the black, when I put it in it made all the difference in the world - I could see the target. I got a lot of help from some experienced match gun shooters (thanks Chris and Phil) and got some feedback similar to what NateG said in terms of front and rear aperture settings - I set the rear ap @ 0.8mm and had the front at 3.7mm with overcast conditions. Chris, who helped me, suggested opening up the front to at least 4.0mm and that helped even more. He was explaining that there will be a point where you will see an effect on having at least 50% of the white around the amount of black (if I remember correctly, based on having the front aperture closed down too far) your shots will be inside your call rather than outside.
Not sure if I articulated that correctly, but there is a lot to learn with these sights and not a ton of info around to refer to. Any more guidance you guys are willing to share or point us to would be appreciated.

 

[DRNewcomb]

I'm just amazed that it's actually a +0.5 diopter lens, vice -0.5. I would have thought thought that the idea was to get the target back into focus, not magnify it. It's a difficult idea to get my head around. I've already got a +0.5 diopter correction in my glasses, so I can see the front sight. But I do see that all the lenses sold for front sights are plus, so there must be some reason for it.

 

[watercam]

The black target at 1000 yds. does become very small without some magnification as the LR target does not increase in size beyond the 800 yd. stage. Focus on the target does not matter as much as the ability to put the black 'blob' in the middle of the sharply focused front aperture. On a day where the targets are in full sun and your rear iris is closed down a bit one can see a fairly focused target - usually one can make out the marking and scoring discs through the sights. Nancy Tompkins book on Long Range shooting is a good resource for all of this and much more. Well worth the asking price.

 

[Pres100]

I'm just amazed that it's actually a +0.5 diopter lens, vice -0.5. I would have thought thought that the idea was to get the target back into focus, not magnify it. It's a difficult idea to get my head around. I've already got a +0.5 diopter correction in my glasses, so I can see the front sight. But I do see that all the lenses sold for front sights are plus, so there must be some reason for it.

I believe the .5 diopter is actually a +1.5 but they call it a .5

Thanks for the Nancy Thomkins reference, watercam. I will check it out.