So we point these things at our target, push the button, and it gives us a number. We know that there’s a laser involved somehow, but just How Does A Laser Rangefinder Work? Turns out it’s an old idea.
The same idea as sonar and radar
Just like sonar and radar, with a laser range finder you send something out and time how long it takes to bounce back at you. As long as you know how fast the thing you sent out can go, then you can figure out – with a little math – how far away the other thing that bounced it back to you is.
With sonar, you send out a sound wave. Like any kid who was taught how to tell how far lightning is, the sound goes about a mile in five seconds. And just like all those WWII movies taught us, ships use the exact same principle by sending out a sound wave and measuring how long it takes to bounce back to determine the depth of that U-boat they’re hunting. A more mundane common use today is the fish finder. Bats use their own version of sonar to fly and find prey.
Radar is pretty much the exact same thing, using radio waves. Those travel much faster of course, but it’s the same principle – send out the wave, measure how long it takes to be reflected, calculates the distance based on the time it took. Other factors like the strength of the reflection and other characteristics can also give useful information, but that’s another subject.
A range finder is like sonar and radar but using a pulse of light
A laser rangefinder works the exact same way, but using a focused, coded pulse of light in an eye-safe laser to do the reflecting and measuring. Like all light, it can be blocked by heavy rain, smoke, a twig, etc. The better range finders will include logic to let you select whether you want the first reflection or to ignore it if there are branches in the way, etc.
The rangefinder sends out the laser pulse and measures the time it takes to bounce back. All this is pretty much instantaneous to us since light travels at somewhere around 186,000 MILES per second. But the machine can handle it.
Used in a variety of applications
Laser rangefinders are useful in many ways. Beyond the hunting applications for which we’re primarily interested here (and that fun game where you hit the little white ball around), they’re used in foresty, industrial applications, surveying, and of course the military. The M1 Abrams tank that I used to ride on back in the day had a very powerful laser range finder that would go out many kilometers.
Again, any rangefinder you would buy for normal consumer use would be eye-safe. The unit on that Abrams tank and other military applications? Not so much.
For more on laser rangefinders and how they work and what they’re used for – including bonus mathematics! – check out this Wikipedia article on how laser rangefinders work.