Eli5: Rangefinder science

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Playing golf yesterday. I played a hole, which distance was very deceiving. I wished I had one of those rangefinders handy and my mind went on this whole tangent of how they work. Some only seem to have one scope, which destroys my only theory of using trigonometry.

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3 Answers

Anonymous 0 Comments

> Some only seem to have one scope, which destroys my only theory of using trigonometry.

The scope is just used for pointing the rangefinder precisely. It actually uses a laser to determine the range.

Light does not move instantaneously, it has a speed (a very high speed). A laser rangefinder will emit a narrow pulse of light and measure the time it takes for the laser to bounce off the targeted object and return, calculating the distance based on the travel time.

Anonymous 0 Comments

They shine a laser at the target and examine the light that comes back. They look for how long it took the pulse to come back (time of flight) to calculate the round trip distance.

Anonymous 0 Comments

Most common modern rangefinders are laser rangefinders, they’re just shooting an invisible laser at something and seeing how long it takes to return and doing the math to determine distance.

The absolute cheapest golf rangefinders are simple monoculars with a reticle (marked lines) that you hold over the flag stick on the green. How tall the flag stick is compared to your reticle tells you the rough distance.

But for pre-laser (or radar) rangefinding, they did use optical rangefinders. Stereoscopic and coincidence rangefinders work a little differently, but they both have two lenses (usually spread pretty far apart), and the user basically adjusts the angle of the lenses until the target is properly in view. Once that’s done, you know the range based on a rangescale on the device. So yeah, probably a lot of math by smart people pre-computers to figure that out.