How Does a Rangefinder Work?

In this article we will be shedding light on how does a rangefinder work, but before that we will get down to the nitty-gritty about the rangefinders. The areas we are covering here include, what is a rangefinder? why is it used and where? Types of rangefinders?

If you want to jump directly on to any specific section of the article, please feel free to follow the table of contents. Lets’s start!

WHAT IS A RANGEFINDER?

A range finder is a binoculars/ monocular type device used to measure distance between its observer and a target.

WHERE IS THE USE OF A RANGEFINDER?

Rangefinders are usually used in golf, ballistics, hunting, forestry and virtual reality. There are many reasons why you may feel the need to use a rangefinder, for example, if you are hunting in the wild, a hunting rangefinder will help you adjust your aim to account for the drop of bullet at relatively longer distances.

Although, with practice one may judge distance and resulting drop, however, a rangefinder provides you with the easiest, quickest and the most accurate calculation for distance and resultant drop. That is one of the reasons why rangefinders are so essential to military operations as well as recreation, alike.

That’s why, in recent past rangefinders have found special place in golf and other recreational activities as well.

WHAT ARE THE TYPES OF RANGEFINDERS?

There are many different types of rangefinders, however, three among them distinctly stand out. These include, Laser, Optical and GPS rangefinders. There are other less used/ purpose-specific types too that include radar, lidar, sonar and ultrasonic rangefinders. We will remained focused on.

HOW DOES A RANGEFINDER WORK?

Each of the different types of rangefinders, whether cheap or pricey works in its own specific way. We will illustrate here the working mechanism of the main types of rangefinders.

1. HOW DOES A LASER RANGEFINDER WORK?

The operation of a laser rangefinder is quite simple, wherein, the rangefinder shoots a laser beam at the target from its emitter and measures the time it takes that beam to strike the target and gets back to the receiver on the rangefinder.

The calculation is straightforward for the reason that a laser beam travels at speed of light, and speed of light is a known speed, therefore, it can be used to calculate the distance to the target.

LASER RANGEFINDERS’ WORKING EXPLAINED

The science behind how a laser rangefinder works is quite interesting. It works around certain principles which are as explained below:

BEAM DIVERGENCE

Targets to which you want to get accurate distance calculation may be varied in size and shape. The process of beam divergence occurs with laser rangefinders and it simply refers to divergence and spreading out of the laser beam fired from rangefinder which is quite narrow just when it is fired from rangefinder.

This divergence occurs because of effects of air in the atmosphere and happens when the target is located over long distances. Beam divergence is essential component of how a laser rangefinder works as the fired beam gets wide enough over long distances to cover the intended target (Fig 1) and when it is reflected back it registers the target back for you (the viewer).

beam divergence image

REFLECTION AND DEFLECTION

The mechanisms of reflection and deflection also play there part in how a rangefinder works and how accurate it calculates the distance for you. Laser rangefinders work best for opaque objects as the beam wouldn’t completely either pass through the object or deflect away at an angle.

There are certain objects that are harder to measure than others. For example, rangefinders wouldn’t work correctly on a pane of glass or a mirror. In case of a pane of glass, almost the whole of beam striking on glass surface passes through it (Fig 2) and is not reflected, thereby without registering a proper reading on rangefinder.

non-reflective glass image

Contrary to a glass surface, when a beam of laser rangefinder strikes a mirror that is at an angled position, whole of light is perfectly deflected away without returning to the viewer/ rangefinder (Fig 3) thus making it difficult to range the target object.

reflective glass image

However, most objects reflect some amount of light nevertheless, making it possible to have some reading regarding the target object.

WHY ISN’T A RANGEFINDER CONFUSED BY AMBIENT LIGHT?

A simple and logical question would be how a rangefinder works in presence of light while it should be confused by ambient light. Well the truth is that laser light emitted by the rangefinder has a specifically different wavelength which is different from that of normal light.

Rangefinders are, thus, specialized to register only that specific frequency of the laser light while filtering out everything else. This specialization helps in ensuring the accuracy that the rangefinders usually have.

Even if the original emitted light is a fraction of all reflected lights from the target, the rangefinder would still register the reflected light from the target that was emitted by it, even if human eye is unable to see it.

HOW DOES A RANGEFINDER CHOOSE A READING TO DISPLAY?

Among the rangefinders, laser ones are relatively faster. At any given time a laser rangefinder emits thousands of pulses on the target object and then, based on the entire data sample, determines the exact distance that is to be reported.

As we have earlier discussed, the laser beam will spread over long distances, therefore it the rangefinder would receive readings from other objects, terrain, backgrounds etc, apart from the intended object itself.

The laser rangefinder is tuned such that it analyses all the data its receiver is registering back from target, and using an algorithm, states the most relevant distance reading for you (the viewer).

2. HOW DOES AN OPTICAL RANGEFINDER WORK?

Optical rangefinders are different from laser ones. They have their own benefits, for example it is not necessary for optical rangefinders to necessarily have a reflective target for proper registration of distance measurements.

With its inherent benefits of having optical basis, the optical rangefinder doesn’t get interfered by weather, atmospheric conditions and surrounding terrain in its measurements.

The principle followed by optical rangefinders is not complex and a basic model can even be achieved by a couple of small mirrors and because of this simplicity of design they are cheaper compared to other types of rangefinders.

It is another matter that optical rangefinders are less prevalent in modern times. It is not easy to find new optical rangefinders from market these days, however, many old ones are still available in antique shops.

Main reason for this is the ease of using laser rangefinders, the advanced features offered by laser rangefinders compared to optical ones and their cheap price.

OPTICAL RANGEFINDERS’ WORKING EXPLAINED

The main operation of an optical rangefinder relies on the principle of coincidence or stereoscopic rangefinding. In case of coincidence rangefinders, images of target are reflected back to you (the viewer) from two different sources (Fig 4).

You, then, align the two images in the instrument, while looking with one eye, thus placing them in “coincidence”. The difference of adjustment made by you for the two images is the marker for determining the distance between you and the target object.

On the other hand, in stereoscopic rangefinders both eyes of viewer are used to see through the instrument and reference markings inside the instrument are then used to determine the distance of target object.

optical rangefinder working image

3. HOW DOES A GPS RANGEFINDER WORK?

A GPS rangefinder presents more accurate readings as compared to other types. It uses satellite links to mark exact positions of you and target(s) in a given location (for example; a golf course).

In order to operate a GPS rangefinder, you will need to have a specific pre-programmed data fed into the rangefinder after which your rangefinder will be able to help you match this data with your surroundings when you use it.

The GPS rangefinder matches the installed data (usually done through a computer or smart phone where target ‘pins’ are preloaded) with your view during operation and gives you exact distance between you and the target flag or hole (also called GPS pins).

It usually is used for smaller areas from around 100-150 meters around the target pin.

GPS RANGEFINDERS’ WORKING EXPLAINED

GPS rangefinders work while comparing relative distances of pre-fed targets and matching that data with your given view of the area. In simpler words, a GPS rangefinder knows your location and many other locations/ pins in the area through pre-programmed data and it has virtually created a relative distance between all targets from you and from each other.

All you do is point to a target and the rangefinder, using available data, and the rangefinder tells you the distance of the target hole or flag.

However, there is a limitation to GPS rangefinders and that is probably the main reason they are not as popular as laser rangefinders despite the fact that they are more commonly available in market compared to optical rangefinders.

This limitation is founded in GPS rangefinders’ mode of operation and dependency upon pre-programmed data. For example, if, while playing golf, you come across an unregistered obstacle or a tricky spot, your GPS rangefinder wouldn’t be able to calculate your distance from this spot simply because you haven’t pre-programmed it in the rangefinder.

This is one of the reasons why GPS rangefinders are still not, even after many advancements specifically targeted at golfers are made in them, a preferred choice for avid golfers for whom a laser rangefinder is both easy-to-use and have more practical use for tricky spots and obstacles compared to GPS rangefinders.

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