One technique that is sometimes taught about using a nonmagnifying optical sight is the use of our binocular vision if the front lens of the sight is blocked or occluded in some way. The method depends on the fact that if we keep both eyes open when engaging a target, our primary aiming eye will see the illuminated reticle (usually a red dot) in the sight while our other eye will see the target. Our brain will normally converge the two images into the perception of being one, and therefore superimposing the image of the red dot onto the target will permit accurate hits.

At least that’s the theory, and it may work properly for most shooters. But not for everyone. A few years ago I conducted a test using an Aimpoint CompML3 sight mounted on an AR-15 rifle, and with the front lens of the sight covered. At the time I reported the results in a thread here:

https://sigforum.com/eve/forum...330003505#4330003505

Because of the increased popularity of optical “red dot” sights on handguns, the binocular convergence method of using a sight if the front lens is occluded has been discussed more recently again. I therefore decided to conduct a similar experiment with an Aimpoint ACRO sight mounted on a SIG model P320 pistol. The test involved firing test groups from 15 and 25 yards with the pistol firmly rested on a support bag. One group was fired with the sight used normally, and then another group fired with the front lens of the sight covered while using the binocular convergence technique to aim the pistol.

These are the two groups fired from 15 yards. The upper 10-shot group was with the sight used normally, the lower with the front lens covered with tape. Note that I didn’t adjust the zero for the second group, so the divergence was the total distance between the first and second group.





The two “groups” fired from 25 yards, upper sighted normally, lower with the front lens blocked. Again the zero of the sight was not adjusted, and that’s why the upper group’s point of impact was left of the aiming point. The second, occluded lens group consisted of 10 shots, only eight of which hit the target backer at all.





Finally I decided to try a more practical test of the sort that an “operator” might use when faced with the need to rescue a woman hostage from a deadly situation. The two faces were about life size and the test consisted of shooting from a rested position at 15 yards after the ACRO sight had been zeroed so that when aiming normally the point of impact was at the point of aim. The final zeroing group isn’t shown, but it measured about 2 inches center to center.

The point of aim at the hostage taker target was between the man’s eyes and marked with the X. The impacts of the five shots fired are marked with the circles.





As I discussed in the previous thread, the large point of impact shifts I experience when shooting using an optical sight with the front lens blocked are evidently due to one or both vision defects that many people are subject to: phoria and binocular convergence insufficiency (BCI). The two defects are not the same, but either can cause the sort of issue I demonstrated above. One or both of the defects are, according to my research, very common in the population.

And therefore the point of all this? If someone tells you that you can achieve accurate hits with your nonmagnifying optical sight even if the front lens is occluded by keeping both eyes open and allowing your brain to superimpose the reticle and target for aiming, it’s something you should confirm for yourself with a test similar to what I conducted.

I mean you almost saved that nice man from that evil bitch.

quote:

Originally posted by cslinger:
I mean you almost saved that nice man from that evil bitch.

Yeah. Lessee now, how can we spin this?
His was but a flesh wound?

Couple of observations (I’m sure by your reputation you are just fine and you know this already)

In my experience, people that struggle the most using this technique are not completely target focused. Despite the occluded lens, they are still trying to “aim” the dot instead of staring at the spot, superimposing the dot in the line of sight, and break the shot.

While most MRDS are somewhat parallax free, when you “aim” the dot instead of staring at the point and sending it, you tend to see the same group dispersion. Drove me crazy for the longest of time.

The other thing is personal vision problems. I can shoot target focused really well out to about 20 yards with irons. After that, I have to lean into the sights a little more. At 50, I have to have that hard front sight focus. My groups fall apart without the proper vision. And it gets me every time. People with vision problems suffer the same problems with dots in my problem.

That’s the two biggest problems I’ve seen.

I took a Ben Stoeger class recently. We discussed training occluded and it was said about half of your dry fire and live fire should be occluded. Me and the boys hit the range on Monday and shot the majority of the day occluded out to about 20 yards at speed.

Thanks for all that.
Some things to consider and explore (when the fire ban is lifted and we can shoot again ).

When I took the Sig Sauer Pistol mounted Optics Instructor course, the first 25% of the class was shot with blue tape over the front of the lens. Logic presented was that all of the cheat codes for the proper operation of the optic (trying to find the front sight to index the dot, looking at the dot instead of the target, closing one eye, etc) are all defeated by a piece of tape, while shooters properly interfacing their eyes to the sihght and the target dont care that the tape is there.

It was sound logic and works pretty well.

I believe that what you are seeing is a form of parallax. I have noticed a similar occurrence in long guns with people who zero with one eye closed and then shoot with both eyes open.

My discussion about phoria and BCI isn’t just something I dreamed up on my own. In particular, if the images from both eyes don’t converge as is considered “normal,” then the technique may not work, or at least not all the time, and that should be obvious from what the technique is based on. If the technique works with no problem for someone, great, but as should be clear from the test I discussed in this and the previous thread, it doesn’t work for me. I carefully controlled both sessions to ensure I got valid results.

I have pointed out that phoria and BCI are not the same thing. As I understand it, phoria is the tendency of the vision convergence to drift the longer one focuses on a spot. If I’m correct, that would explain why a quick shot when using the two eyes open and focusing on the target might be more accurate than if we’re taking more time for precise accuracy. The BCI defect, though, is evidently not focus time dependent.

It’s interesting to learn that some trainers have shooters practice extensively with the sight occluded. That’s something I’ll have to ponder for my own purposes. In my own experience I discovered that the “find the dot” bogy wasn’t fearsome as I anticipated, but maybe that’s because I cheat somehow.

In any case, for anyone who anticipates that they may find themselves in a gunfight and for some bizarre reason only the front lens of their optical sight is blocked, determining how well the binocular convergence technique will permit them to deliver accurate shots is simple and easy. That’s what this thread is about.

quote:

Originally posted by DaBigBR:
I believe that what you are seeing is a form of parallax.

I also believe that parallax error does have an effect at the longer distances. I think that may have been part of the reason why the 25 yard occluded pattern was so large, and is something else trainers who blithely say, “Just shoot with both eyes open,” should be aware of. It’s commonly claimed that optical sights like the ACRO and others are “parallax free,” but that’s simply not true, and is something else that anyone who understands the phenomenon can confirm for themselves. Under normal circumstances parallax errors with such sights are very minor, but using the sights with the front lens blocked isn’t normal.