How Do Laser Rangefinders Work? (Everything You Need To Know)


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How Do Laser Rangefinders Work

Do you remember the day when laser rangefinders were the new thing?

Now, they’ve evolved into these smart, Bluetooth, do-it-all devices.

Do they really do it all?  

It’s time to get deep into the details about how rangefinders work and how to understand their capabilities and limitations.

With this information under your belt, you will know how to choose the right rangefinder and how to maximize it for your intended application.

Let’s lase under the rubber armor and metal housing to see the magic underneath.  

What is a Laser Rangefinder (LRF)?

Holding Bushnell Prime Rangefinder in palm of hand

A laser rangefinder is a handheld monocular that uses a laser beam to acquire a distance on a target.

That is the gist of it in the sports optics industry. Physically, there are expected features of a rangefinder that will be consistent across various models and manufacturers.

  • Magnification: 4-10x
  • Objective lens size: 15 - 24mm
  • Compact: 3.8 - 7” (L)
  • Lightweight: 5 - 16 oz
  • LOS (Line of Sight) distance

There will be variations and exceptions beyond these standard specs. Take for example, the other type of laser rangefinder, a rangefinding binocular. Obviously, these specs will largely differ to that of the monocular. This brings us into categorizing rangefinders according to how they perform and appeal to those in the market.

Thanks to advancements in technology and the ever-increasing affordability of gadgets, laser rangefinders have quickly found their place in the sports optics realm.

With well-known, trusted, and world-class manufacturers putting their stamp on the measuring-savvy units, it's no wonder that more consumers are getting their hands on them.

How do Laser Rangefinders Work?

Why is this need-to-know info?

Isn’t it enough to know that when you push the button you get a distance?

For those who are not appeased with staying ignorant, knowing the science behind its function helps to determine what LRFs are better than others. With this knowledge, you can determine if a Leica is worth paying more for or if you can get away with an average unit for average hunting conditions and distances.

Let’s break it down.

  • LRF emits a laser beam that travels at the speed of light.
  • Beam reaches target, scatters in various directions, and a portion of reflected beams return to the rangefinder.
  • Internal circuitry is timing the laser beam from emittance to reception (time-of-flight measurement).
  • Ranging engine provides a linear distance to the operator.
How Laser Rangefinders Work

As you can see, it’s a straightforward process. But what about when it’s not?

There are many factors that can determine a successful scan return. Some are within your control and others are not. This obligates us to get more in-depth about the workings of an LRF.

Laser Rangefinder Performance Factors

We call the primary aspects that affect LRF quality and function “performance factors.” Knowing about such performance factors can help you determine what to look for in a rangefinder be it for rifle hunting with ballistics, precision shooting, or bow hunting with angle compensation.

Optical Quality

When you buy any optic, binocular, spotter, or riflescope, you depend on the glass to see, spot, and make out details of a target. The same is expected of a rangefinder. Glass matters!

Magnification also matters.

  • Low power LRFs are nice for handheld use and shorter ranges.
  • High power LRFs are better for longer ranging and better seeing – at least you expect them to be. They should be tripod mountable to achieve stability for precision aiming of the reticle and laser.

However, high quality glass with quality coatings can make up for low magnification. There’s a balancing act to consider, and ultimately, if you can’t see your target, you can’t range it.

Receiver Aperture

Knowing that the LRF receives reflected wavelengths of emitted laser energy, it makes sense that the receiver aperture size is an important factor. Although essential to optical resolution and brightness, it also allows for how much return data can be acquired for sensor processing.

Generally, the larger the aperture, the more return data and light can be “collected.” This can improve ranging distance performance and overall accuracy.

Reflective Targets

Bushnells LRF 850 Bone Collector rangefinder review
Image Credit - Bushnell

When you see the advertised range of an LRF, it’s usually always the max distance the LRF can acquire on reflective targets. Generally, manufacturers will break this down even further.

  1. Reflective targets are objects like steel or where there is a lot of reflected light on a surface like a shining rooftop or wet rocks that have better reflectivity for the laser beam to bounce off. This equates to target that can be lased at max range.
  • Medium reflective targets could be considered trees and rocks. This equates to targets that can be lased at usually half or around 75% of max range.
  • Soft reflective targets are things like animals. The color of the target also affects return scan data. Black targets like black cows have been said to be hard to range in the same way that it’s difficult to range targets in shaded areas. The ranging distance for soft targets could be as low as 45% or as high as 75-80% of max range.

The medium and soft ranging distances will always be less than the advertised, maximum distance. We provide insight about reflective vs non-reflective targets here.

Target Size & Position

Besides reflectivity, the target size, position, and shape must be considered. Obviously, a deer standing broadside at 300 yards is going to be easier to range than an 8” steel plate at 1000 yards. Yes, the plate is reflective, but it’s significantly smaller and beam divergence will rule in this case. What if that plate was on its side? Goodluck getting a return scan.

Atmospherics

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It’s your drawn week and it’s snowing. You’ll get your Merino wool gear on and head out anyway. It’s too bad that tagging out may be prevented by your optics.

Rain, snow, sleet, fog, bright sun, time of day – you name it, they all affect LRF performance. If you take rain as an example, the laser is interrupted or reflects off raindrops and provides a return scan that is much closer than the actual target. Keep ranging and you’ll probably get multiple, different readings. This amounts to complaints about inaccuracy and false returns.

When manufacturers test out their rangefinders, it’s usually under ideal conditions, i.e. sunny with a little cloud coverage, tripod mounted, and on large, highly-reflective targets!

To help the user overcome such annoyances, LRFs will provide various target modes. These programmed algorithms allow the LRF to focus laser beam emittance at what it thinks you want to target. The most familiar target mode terms are Best, First, and Last. Remember, they’re not foolproof but may help in certain conditions.

Some manufacturers will claim Fog modes, Brush modes, and Golf modes. They’re really just named for the application or condition you’ll be using it in. Behind the fancy mode name, they are really just programmed approaches of how a rangefinder analyzes the return scan data, i.e. target modes.

Vibrations

Rangefinders are primarily used freehand. High magnification can make it difficult to hold steady without tremors, shakes, and vibrations. Leaning against a solid platform is the fastest way to acquire stability to get the reticle still and on the target. In turn, it allows the laser to hit the target you are trying to range with improved accuracy and precision.

For very long ranging LRFs, especially ones with high power (above 7x) and over 3000-yard performance, tripod mounting the unit is the better option.

Not all rangefinders, monocular and binocular alike, come with thread-in screw points for mounting to a field tripod. Manufacturers may have their own strap, belt, or bracket mounting systems available to correct for this.

Beam Divergence

This could have a topic all its own, but we’ll give you the rundown here.

The laser beam has shape and size that affects how it gets a distance on a target.

Not all manufacturers release the beam divergence specs of their rangefinders. It can be helpful to know this spec, but it’s extremely important to remember that it’s not the only part of the equation.

For example, a 2 x 2 mrad beam divergence is 2 mrads tall and 2 mrads wide. At 500 yards on a deer size target, you may not need to worry so much about divergence, but at 1000 yards or with smaller targets, it will be critical to precision.

If you were ranging a 30” IPSC target at 1000 yards with the above beam divergence, the beam is going to pick up a lot of background “noise.” The rangefinder may not be able to provide a return scan, or it may pick up on other reflective targets around it. Why?

The further out the beam goes, the less powerful it is, and the likelihood of it reflecting off unintended targets increases.

  • Tight, small, or minimal beam divergence specs, however it’s expressed, are desirable for ranging small targets at max distance. However, because they’re so unforgiving with vibrations, small beam divergence LRFs should be tripod mounted since precision aiming will improve accurate return scans.
  • Large beam divergence LRFs can be easier to use freehand, and most of the time, you can depend on return scan data. However, it could be less reliable because laser energy dissipates over a wider span across distance. To differentiate whether it’s returning a distance on your intended target and not the large rock behind it, you may need to rely on the LRF’s targeting approach mode.

Target Modes

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Dovetailing from the Atmospherics subsection, target modes are responsible for how the rangefinder analyzes the return data. Manufacturers don’t tell us the details on the preprogrammed algorithms they’ve used, but they do tell us what target modes they provide (most of the time) to give us a better idea of performance and appropriate application.

The most common target modes are:

  • First: Closest readings on the closest target within the beam divergence. There is also a variation of first target mode that takes “spike” readings into account. It looks for peak patterns in the return data – the closest target with the most readings.
  • Last/Second: Furthest readings on the furthest target within the beam divergence. There is also a variation of last target mode that takes “cluster” readings into account. It looks for the largest cluster of readings in the return data around the range that it thinks you are ranging.
  • Best: Manufacturers don’t provide much detail about their “Best” target mode. They say it’s the mode that is best for reflective targets from minimum to maximum range that the rangefinder is advertised for – that’s it. It’s usually considered the Normal or Standard target mode.

Based on this limited information, it can be assumed that they are using a spike-like approach where the LRF looks for the highest number of readings in the return data for the single distance you are ranging. It’s usually the most reliable target mode for most ranging purposes.

Return Scan Times

There are two sets of response times to be aware of: the time it takes to get a reading and pulse rate.

The time it takes to get a reading from a rangefinder will vary between manufacturers and models. Most provide a reading within a second while Leica is known to provide readings at 0.3 seconds – well-nigh instantaneous.

Some rangefinders may take longer depending on the types of algorithms it must calculate across longer distances. For example, equivalent horizonal ranges across 800 yards may take longer to get a reading than an LOS distance at any range.

With as much as LRF technology is improving, response time is rarely an issue. It’s usually the power and wake-up-from-sleep mode timings that gains the most criticism.

Scan mode helps to minimize timing frustrations as the refresh rate (acquiring readings) is typically done 3-4 times in a second.

What is pulse rate? Time-of-flight measurement is the operating principle of a rangefinder. The LRF is firing multiple laser pulses simultaneously, and the return data is analyzed by providing an average while weeding out the weak signals to give the user an accurate reading.

But pulse rate is not the end of the story. All other LRF features must be considered as a whole in regard to performance. However, it does motivate one to understand how errors are detected and how accurate the sensor software is.

Ranging Engine

This is the combination of components necessary to have and use an LRF. Primarily, it includes the laser transmitter, receiver, and software and sensor that powers the rangefinder tech.  

Manufacturers have their own rangefinder engines that are better than others and others even better than that. Other rarely known factors include timing circuitry, pulse duration, laser output, and wavelength specs, and they are not often released by the manufacturer. But that’s another rabbit hole for another day.

Angle Compensation

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This is a rangefinder’s ability to provide the equivalent horizontal range. For the longest time, only the linear LOS (Line of Sight) distance was provided by rangefinders. This meant that you needed to pull out paper and pencil and hope that you remembered everything in trigonometry class. Either that or cross your fingers and hope that you’re on target – not smart.

These days, nearly every rangefinder has angle compensation as a standard feature. It has a built-in inclinometer that measures the angle of the incline or decline relative to your position and the target. It does the math for you and provides a true horizontal range – the distance you would set your bow sight pin for, holdover on your reticle, or dial adjustments for.

Applied Ballistics

Preloaded rifle and load profiles on a rangefinder was the next big thing after angle compensation. You could select an onboard profile and have bullet trajectory data necessary to make the shot. While it had a lot of shooters excited, it introduced a new set of problems that required improvements and new tech to address them in later, smarter models.

  • Preloaded options were limited.
  • Preloaded options could not be edited or customized.
  • Not all rangefinders allowed for manipulation of atmospherics and environmental factors.
  • Those that allowed customization or transfer of ballistic profiles required a micro-SD card.

Preloaded ballistics are still common today. But Bluetooth has entered the rangefinder industry and has allowed a significant opportunity of customization, real-time data, and instant dope info right to the display of the LRF.

Even so, connection to a smart device for accessing these features through the manufacturer’s app or third-party ballistic solver still has its limitations. Ease of use of the app, paid subscriptions, limited dope info to a max distance, limited user profiles, syncing issues, firmware issues, and the list goes on.

However, with Bluetooth technology, some rangefinders allow for bypassing limitations via syncing a Kestrel or Garmin with Applied Ballistics devices. Finally, you get to integrate your Kestrel with a binocular rangefinder! How’s about that?

Respect the Rangefinder

For a small device and with basic understanding of its operating principle, it’s easy to underestimate them and complain about the price. The level of engineering and manufacturing of rangefinders are far more complex than we can write about in one day.

An LRF is emitting laser energy at the push of a button firing hundreds to thousands of pulses. Software determines weak signals from strong ones, clusters from peaks, and then averages the results. It still has to calculate for the parameters that you have set with the preloaded features like measuring in yards or meters, using a target mode, or whether you’re on an incline, and if there’s a 10 mph wind at a 45-degree angle.

All this is done within microseconds, and it’s something to be impressed by. Add to that smart capabilities, rugged exteriors, and high-grade optics. This is technology that demands respect. We don’t see you doing math like this with Superman vision.  

Respect the rangefinder and remember it’s still a tool. They’re not infallible devices.

At the end of the day, you are the one responsible for the decisions you make in the field.

Just because your LRF can range hide at 1600 yards, it doesn’t mean you should ethically take the shot. Close in.

Range the Informed Way!

Rangefinders are extremely helpful to sight-in scopescompete in target shooting matches, and to tag out on a hunt.

Like any other gadget, it exists for your convenience, enjoyment, and success.

Getting the most out of your rangefinder means buying one that best suits your needs and knowing how to use it. At least you now know how they work.

Congratulations, you are now an informed buyer.

Identifying the best rangefinder should be a piece of cake now that you know what to look for.  

Happy ranging!

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