A little bit of mental illness can make you professionally successful. It is generally recognized that Elon Musk, for example, likely falls someplace on the autism spectrum. He seems to be doing fairly well. A whole lot of mental illness, by contrast, can make you intolerable to be around. In my case, I have just a smidgeon of OCD.

Shooting 101: Understanding How Red Dots Work

A tiny bit of obsessive compulsive disorder ensures you remain attentive to details. That makes you a good physician and a diligent writer. It can also make it tough to let things go. Such was the case for me when I first met a red dot sight.

Just in case you’ve been living underneath a rock someplace, electronic optics are absolutely everywhere these days. They ride atop everything from tiny pocket pistols to helicopter-mounted Gatling guns with everything in between. Red dots draw power from either a compact battery, artificial room light or the sun. They make typical target engagements faster, easier, and more accurate. However, there was always one particular aspect of their operation that I never could quite get my head around. My persistent failure to understand the fundamentals of how red dots work was like walking around with a rock in my shoe. It just ate at me, like, for years. I think I finally figured it out.

Pathophysiology

Most humans past about 40 begin to suffer from presbyopia. When we are young, the lenses in our eyes are soft and pliable. Working in concert with the ciliary muscles, the lens allows us to focus on detail work up close and then instantly shift to distance when we see a pretty girl or an oncoming train. Over time, however, the lens gets stiff and will no longer accommodate. The practical result is that most people of a certain age can focus on distant objects but lose the ability to see clearly up close. That’s the reason guys like me wander about with reading glasses perched jauntily atop our heads. Older people often describe it as their arms getting shorter, because they can no longer hold reading material far enough away to digest comfortably.

What ate at me so badly was the observation that a red dot sight was crisp and clear in my own field of vision without my readers. Sans reading glasses I can no longer focus on a front pistol sight to literally save my life. However, that tiny little red dot floating right at arm’s reach was inexplicably crisp and clear. It was as though the dot was not on the pistol but was rather hovering out over the target. Holographic gunsights exhibited similar curious behavior. I Googled my brains out and never could figure out why that was. Then one of my rocket scientist relatives built a red dot sight from scratch, and I got to see what the entrails looked like up close. That’s when I think I figured it out.

Technical Details

I’m nothing special myself, but I do come from a really smart family. One of my tribe built his own DIY red dot optic using a 3D printer and stuff he sourced on the Internet simply as an intellectual exercise. Seeing what went into one of these things was indeed illuminating.

In 1862, an English scientist named John Henry Pepper debuted a clever theatrical trick now known as Pepper’s Ghost. In this case, an actor out of the immediate sight of the audience, brightly illuminated so that his reflection appears on a large pane of glass on the stage. With the glass kept really clean, the subsequent spectral image seem to float above the viewing space. This technique continues delighting viewers on the Peter Pan and Haunted Mansion rides at Disney. Red dot sights employ a variation on that theme.

A red dot sight includes a light-emitting diode that shines at an angle against a spherical reflector and then bounces back toward your eye. The reflector has a special coating that only reflects red light. The red dot is clearly visible, while your view of  the world remains unimpeded through the optic. As light rays are vectors that travel in a perfectly straight line, by adjusting the geometry of this LED you can zero your optic and have it shoot straight to point of aim. All that was pretty easy to understand, but it still did not explain the focus thing.

The Epiphany

Red dots operate like a laser sight in reverse. A traditional laser sight obviously projects a laser dot onto a target. By contrast, a red dot only operates between the sight and the shooter’s eye. As a result, there should be no evidence of the dot that is visible to the target. Outside light can reflect off of the glass, but the red dot itself does not project downrange. It rather shines directly onto the back of your eyeball. That was the key to understanding the curious physics involved.

The human eye is one of literally countless miraculous contrivances God designed into this magnificent human machine of ours. The image of stuff that you see is projected inverted onto your retinas much like the sensor plate of a digital camera. Your brain then flips this image upright and processes it quickly enough to allow a combat helicopter pilot to safely fly his machine nap of the earth at 150 knots and five feet off of the ground. The wiring for those images actually gets split and jumbled in a simply breathtaking way in a place called the optic chiasm before being reassembled and processed in the occipital lobe of the brain. It really is miraculous in its complexity.

Projecting the Dot

In the case of a red dot sight, the dot actually projects not onto the target but rather back onto that inverted image already present on your retina. Red dots are always built around eye-safe emitters because the light is fired directly back into your eyeball. Additionally, because the dot is essentially a single point, the image is not subject to much of the refraction error that my reading glasses are there to repair. An analog might be looking at a near object through a pinhole. Doing so will typically produce a small but crisp image despite the up close nature of the target.

That is the reason the dot seems crisp and clear to my aged eyes despite originating a mere eighteen inches or so from my face. The geometry of the thing will keep your firearm on target no matter what angle you look through the sight, even if the glass is cracked. If you can perceive the dot over the target and the reflector’s geometry is intact, the gun is lined up properly.

Your dominant eye receives the dot, and your brain superimposes it over your field of view with both eyes open. The end result offers the same quick reaction time and superlative situational awareness as might the heads up display in a fighter plane. And to think all that actually occurs inside your skull. That was my eureka moment.

Ruminations: How Red Dots Work

There is actually still way more to how red dots work than that. The vagaries of refraction errors and astigmatism are beyond the scope of this project. However, the epiphany that the pinpoint dot actually designated not the target but rather the image of the target inside my eyeball solved the quandary for me. I couldn’t wait to share that revelation with you, my shooting buddies.

Both my home defense rifle and handgun sport top-quality electro-optical sights. I now hit the range secure in the knowledge that I understand the physics behind the way my eyes process the data from my gunsight. That makes me a better shooter.