Tag: rangefinders

The Technology Behind Your Rangefinder

Laser rangefinders all work along those same lines, there is a lot of room for innovation around the implementation details. I recently reviewed 8 of the top laser rangefinders used for hunting and long-range shooting and was shocked by how much variance there was in their performance.

Ranging performance depends on many factors, but here are the biggest differentiators between rangefinders when using them for long range shooting or hunting. I’ll touch on most of these in more detail throughout the article. Special thanks to Mike at Range Finder Now for talking through this with me and putting so much thought into this list.

Ability to spot the target– This means good quality optics with proper magnification. You can’t range the target if you can’t find it. Most shooters opt for an 8x or 10x magnification. While doing field tests on rangefinders we searched a field for targets using 5x magnification, and we thought we ‘d found all the targets. However, after searching again with 10x magnification we immediately saw one more target that we ‘d completely missed with the 5x unit. Like I’ve mentioned in other posts, really good glass can sometimes make up for magnification. I can see more detail on a 2000 yard target using a 45x Leica spotting scope than a 60x Bushnell spotting scope. The point is quality glass and appropriate magnification both matter, and you can’t totally ignore one or the other.
Ability to get laser energy on the target– This has a lot to do with beam divergence, which is a description of how “focused” the beam is. There are a few trade-offs between a very tight or larger beam divergence, which we’ll talk about later in this article. There can also be a difference in the quality of the laser pulses transmitted, in terms of the type, wavelength, and sharpness … although those things can be very difficult to quantify.

Receiver aperture size– This is the size of the opening on the receiver optic that captures the return readings and sends it to the actual sensor. A larger aperture can have a huge impact on how much return data the unit is able to collect, which can allow the unit to perform at greater distances and can help the resolution/accuracy of measurements at a shorter distance as well.
How the unit analyzes results– There are a lot of differences between how rangefinders interpret the readings once they receive them, and some are much smarter than others. Older models simply displayed the first reading that returned to the unit, but many modern rangefinders use “multi-pulse technology.” This approach emits a burst of hundreds or even thousands of small laser pulses over an extremely short period of time. It then collects a large sample size of readings, then analyzes those results to identify/ignore outliers (like brush, fog, rain) and determine the reading you are intending to range with more certainty. More beams emitted can also help the odds that you’ll get a reading on a small and/or non-reflective target. The logic and algorithms used to determine what to display to the user can have a major impact on how well a rangefinder performs.

Beam Divergence– The Ability to Get Laser Energy on Target
Beam divergence, also referred to as beam dispersion, is an angular measurement (typically in mils) of how “focused” the laser beam is. Smaller beam divergence provides greater ranging precision and greater max distance in most situations. With rangefinders of similar quality, beam divergence can be a major indicator of ranging performance. If you can focus 100% of the laser energy on the intended target, you have a much better chance of getting multiple readings off of it. If a rangefinder is smart in how it analyzes the readings, it can make up for less than ideal beam divergence … so contrary to popular belief, beam divergence is not the only factor to consider.

Rangefinder Beam Divergence Diagram

To understand beam divergence, think of shooting two rifles at a target 1000 yards away. One of those rifles averages 2.5″ groups at 100 yards, and the other averages 1/2″ groups. Which of those would give you the better chance of hitting your intended target at 1000 yards? Now if you are trying to hit a 12″ target at 300 yards, either rifle should work. But as you stretch out the distance (or shrink the target size), the smaller divergence becomes critical. This is the same for beam divergence on laser rangefinders. If you are ranging relatively large (deer size) targets at ranges under 500 yards … there is probably no need to worry about beam divergence. As the targets get further or smaller, beam divergence quickly becomes critical to accurate ranging.

I’ve heard of beam divergence as large as 4 x 2 mils, and one military-grade model I’ve tested was under 0.3 mils … so there is a lot of variance out there. Here is a diagram that illustrates how big of a difference beam divergence can be at 1000 yards.

Rangefinder-Beam-Divergence-at-1000-Yards

One scenario where a very tight beam divergence may be a drawback is if you are trying to range a distant target offhand (i.e. not supported by a tripod). In that case, the motion caused by the unsupported position may make it difficult to hit the target precisely with a tightly focused beam. On the other hand, if you had a beam with more divergence you could more easily hit the target even with some wobble and then rely on the rangefinder’s “smarts” to determine what you were intending to range within that larger window.

Example-Where-Tight-Beam-Divergence-Could-Hurt

I was talking to a representative from Vectronix, and we both agree that a beam divergence around 1.5 x 0.5 mils is probably ideal for targets in the range of 500 to 2000 yards, although that isn’t a hard and fast rule.

Factors Affecting Measurement Range
There are a number of factors that influence how well a rangefinder is able to perform, including target properties, atmospheric conditions and rangefinder support, and those all play into the maximum effective range of the unit in a given scenario. Here is a very helpful diagram provided by Vectronix that illustrates what those are:

Vectronix – Factors Affecting Measurement Range

When manufacturers advertise a rangefinder to have a max range of 1000 yards or 1 mile, you can usually translate that to meaning there is a chance you might get a reading at that distance, but only under absolutely ideal conditions (e.g. low light, off a tripod, on a very large, reflective target). In my experience, you will usually only be able to get readings out to 70-80% of that advertised max distance under most daytime conditions (bright light) on a 2 MOA reflective targets.

Understanding What the Rangefinder “Sees”.
The easiest way to understand how rangefinders work is through a quick example. The diagram below shows a couple tough ranging situations, with each of the yellow targets highlighted by a red box meant to indicate the related beam divergence when trying to range that target. You can see in each situation there will likely be readings returned for the tree, the target, the near hill, and the far hill.

Long-Range Rangefinder Beam Divergence.

The next few illustrations show what the rangefinder might “see” when it tries to range one of our tough scenarios. The first diagram has a grid of just under 200 boxes. You can think of that as all of the beams emitted by the rangefinder. The blue boxes indicate beams that were reflected back to the rangefinder that it was able to record as readings. Boxes that aren’t marked blue mean the rangefinder didn’t get a reading back from that beam, which may be due to things like poor reflectivity (e.g. the tree doesn’t reflect as well as a metal target) and angled objects (e.g. the hills are at a shallow angle away from the user, instead of directly perpendicular like the target).