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If you are in the market for a laser rangefinder and want to be able to choose and use one effectively, it is important to understand exactly what a laser rangefinder is and how they work. This brief article cannot hope to be all inclusive but can provide a solid overview and get you well on your way to knowing everything you need to know about a laser rangefinder.
What Exactly is a Laser Rangefinder?
There are four primary components of a laser rangefinder that are vital to how it functions and how we use it. What this means is that a rangefinder is actually four different devises that have to be tuned to perform together with exacting accuracy if you want a total unit that works. If any one of the four pieces is sub-par, the whole unit will be affected.
The four individual devices are:
Monocular or Binocular
Just like any other optical device, the quality of the glass and how much magnification you have will have a direct bearing in your ability to accurately hit a target with the laser and get a good reading. Glass that is dull or cloudy will limit the range of your rangefinder no matter how good the rest of the parts are.
Most laser rangefinders use an overall weak laser, usually a class 1 laser that is eye safe. While it may seem more beneficial to use a more powerful laser, there are a lot of advantages to using the weaker laser. No matter what, the laser light will travel at the exact same speed and that is the most important aspect of the laser.
Older rangefinders and a few of the cheaper ones still rely on sold beam lasers but the more modern and accurate models use pulses of laser light. This allows more exact readings and allows you to be more accurate when sighting your target.
The principle of a rangefinder is to emit a pulse or beam and then catch the reflected light. The receiver is what captures this light. Some factors that will affect the ability of the receiver to get a good reading are sensitivity and aperture size.
A more sensitive receiver can read signals that are weaker and have travelled a longer range but will be more susceptible to false readings from other light sources. The size of the aperture will allow the unit to capture more readings that may have been thrown off from a direct return to do target angle.
Inside each rangefinder, there is a microprocessor that is responsible for doing all the math and calculations that translate the time it took for the laser to make a round trip into a reading on the range to the target. The more advanced the computer, the faster the calculation will be and the more complex calculations it can do in a given time.
In a modern rangefinder, the computer is usually of sufficient power. It is the program that handles the data that can be inferior in cheaper products.
How Does a Rangefinder Work?
Now that we understand the very basics of the parts of a rangefinder, we can look at a very elementary example of how it works.
The process begins when we have spotted a target, let’s say 1000 yards away, through the optics and press the button to send the laser down range. We will assume we are using a quality modern rangefinder that emits a pulse of laser beams.
We will also assume a commercial rangefinder as professional or military rangefinders may work with an entirely different technology. Most commercial rangefinders use ‘Time in Flight’ to calculate range. The longer the beam takes, the farther away it is.
From the Unit to the Target
While it’s easy to assume the laser will fly perfectly straight, that would be incorrect. There are several factors that can affect the way the beam travels.
The most devastating of those would be anything between you and your target. This could be anything from leaves, weeds, brush, or any other visible barrier. It could also be water vapor, dust particles, smoke or other things that you can’t see with the naked eye.
The second factor is vibration of the unit either by shaking of the hand, your pulse, or anything in the environment around you that is emitting sound. Generally, the amount of deflection caused by these are very small.
The fact that our example rangefinder emits a pulse is a bonus, even with some of the light being deflected, a few will hit our target a thousand yards down range and begin their return journey. Since light could travel around the earth 7 ½ times in one second, the amount of time this took is incalculably small.
Speaking of incalculably small, most of the deflections you will experience could be fractions of a millimeter over 1000 yards. Just a point to keep in mind.
From the Target to the Receiver
Since we have a laser pulse and some of the light was deflected away from the target or was interrupted and reflected back before hitting the target, we will get different results back from each beam of that pulse that hits our receiver.
All of the same factors that affect the beam on its way to the target will also affect its return trip. Additionally, the angle of the surface and how reflective it is will affect the return of the light. A target that is less reflective will return a weaker signal. A target that is angled will send the beam off at a different angle. The pulse may have sent out hundreds of small beams. Some of them will hit the receiver.
Calculating the Results
This will be a very simplified explanation of the way calculations occur. There are a variety of methods used to calculate results and many companies have a variety of different ways of handling those results. Understanding every possible method would be a massive undertaking.
In short, the computer will look for trends in the results to try to determine what reflected values came from your target and what ones can be discarded as errant beams. The predominant two methods used in a pulse rangefinder are clusters and spikes.
A cluster reading will look for the most returned beams in very close range to each other to try to identify what you were pointing the rangefinder at. If you range a target and the rangefinder gets 7 readings back that are very close together, it may assume that is the target. Sometimes this can be the most accurate, especially at closer ranges.
Spikes are measured by the number of returned values at the same range. If you were to get back 6 readings that were in the same range or VERY close to the same range, it would be a spike. At longer ranges or when there are a lot of various surfaces throwing off beams, this is typically more accurate.
Some of the most advanced units may use both methods and even some proprietary methods between. When the calculations are complete, the range to the target will be displayed. Considering the speed of light and the speed of modern processors, the time elapsed should still be well under a second.
While this is a very simplified explanation it should be sufficient to allow you to become more proficient with a rangefinder. Understanding the mechanics of a laser, the limitations of the receiver, and the incredible complexity of the calculations would take a book or more. Things have come a long way since those early models.
This explanation leaves out some of the finer details of rangefinders used in hunting which may have additional calculations to help you with a rifle or bow. If you want to know more about hunting rangefinders, check out our article here.
The important points to take away from this are:
- Time in Flight = Distance
- Rangefinders use a pulse and not a single beam
- Any obstruction from leaves to water vapor cause issues
- The computer is smart enough to get around most issues with obstruction
To avoid most issues with a rangefinder, buy a high-quality unit, use a tripod, and practice like you would with anything else. Head to the firing range and use pre-marked targets with known range to make sure you are getting a good reading.
Persistence pays off. Range every target twice. Good luck!