鉄砲道 — teppoudo

Vision is a complicated process. The human brain is constantly taking the images from each eye and combining them to render a single image that we see.

The disparity in the images comes from the fact that the eyes are almost never aligned parallel to each other. If you draw a straight line from each eye, based on the direction it’s looking, the lines will intersect at some point. This point typically aligns with the object that you’re looking at. The position of the eyes is commonly referred to as eye alignment. I’ve also heard some people refer to this as brain focus.

The second thing that happens when you “look” at an object is that the muscles in the eye adjust the lens to focus and produce a clear image. This is commonly referred to as eye focus or lens focus. This is analogous to how a camera lens focuses.

When we’re normally seeing, the brain is constantly adjusting the eye focus to make the object we’re looking at clear and adjusting the eye alignment so that the eyes intersect at the object of interest. Some aspects of this image are in focus and others are not in focus and there are double images in the scene, however we tend not to notice this since we’re generally paying attention to a small part of the scene being rendered in our brain.

The fun starts when we try to align multiple objects such as the iron sights on a pistol and a target with both eyes open. Please refer to the post on stereo vision for details of the issues.

As discussed in the stereo vision post, I’ve finally managed to figure out how to shoot with both eyes open. However given the issues I’ve been studying the reason why I’ve been able to get this to work.

It occurred to me that if the eye alignment intersected at the target and the eye focus for the “sighting” eye was on the front sight, I’d have the ideal setup.

I’m not completely sure that this is what I’m doing, but I suspect a subconscious change in eye alignment, is what has given me the ability to get rid of the ghost image of the target and shoot comfortably with both eyes open.

The sights are clear to me and the target is still blurry, so I suspect that my focus distance for both eye lenses is at the front sight distance. I don’t know if it’s even humanly possible to focus each lens at a different distance (right eye on the front sight and left eye on the target), nor am I sure that it’s even a good thing.