As hunters head into the field this fall, I’d wager most will have a laser device close at hand. The most common device will be a standalone laser rangefinder, but some will have a binocular with a laser rangefinder built in. Others will have a riflescope equipped with a laser rangefinder and some will have used a laser bore sighting device to assist in sighting in their rifles or aligning their bows. And, of course, there are tactical laser sights which project a visible dot onto the target, indicating where the bullet will hit. Lasers are everywhere. So far, I haven’t seen one integrated into a smartphone, but I’m sure somebody somewhere is working on it.
The prevalence of lasers means it’s time to look at the technology to ensure hunters understand their operating principles, know how to test a laser device and can get the most from their lasers. Since rangefinding devices are the most common, we’ll focus on those.
The first laser was built in 1960, with the term being an acronym for “Light Amplification by Stimulated Emission of Radiation.” A laser differs from other sources of light in that it emits light coherently. It’s this spatial coherence which allows a laser to be focused to a tight spot and keeps it from spreading as widely as, for example, a flashlight beam. In the visible spectrum, red and green are the most common colours, but there are, of course, non-visible lasers, which is what we have in our rangefinders. Also, lasers are not necessarily a continuous beam. For many applications, such as in rangefinders, laser beams are sent out as pulses.
Along with the ability to transmit a laser pulse, a rangefinder also has the capability to detect the reflected pulse’s return. The instrument measures the length of time from sending to receiving and calculates the distance of the object based on the time differential.
Naturally, that distance measurement needs to be accurate. I’ve tested quite a few over the years and have never encountered a laser rangefinder which was obviously inaccurate. However, if you want to test your rangefinder, call the nearest technical institute/college which teaches surveying. They’ll have a place where they go to calibrate their laser measuring devices, and if it’s accessible to the public (mine is) they’ll let you use it. Another alternative is to gather several rangefinders and range the same point(s) with all of them. If they all agree, it’s a good bet they are all accurate enough.
But here’s a more important point. When sighting in a rifle, use your rangefinder to establish the range to the target, don’t take the gun club’s word for the target distance. It’s not unusual to find a 200-metre target frame is actually more or less than the listed distance. And sometimes the distance-to-target depends on which bench you’re shooting from. So, always range your sighting-in target and then run whatever ballistic program you’re using based on the information provided by the rangefinder. This also helps compensate for any error in your rangefinder when used in the field.
To really understand lasers, it’s important to realize that although visible laser beams appear to stay tightly and uniformly focused over their entire length, they do widen as distance increases. This is called beam divergence, and, of course, they have much less divergence than that flashlight example mentioned earlier. However, not all lasers are created equally, and some devices on the market have less beam divergence than others. Unfortunately, I don’t know of any reliable way for the consumer to test beam divergence, so we’re stuck with taking manufacturers at their word. Hopefully, they would never inflate (or in this case deflate) these numbers to make themselves look good.
When you do look at beam divergence numbers, be aware they are usually expressed as an angular measurement, in milliradians. If you are a long-range shooter who uses the metric system and adjust your scope in mils, you’ll be comfortable understanding these numbers. For imperial shooters, who use minutes-of-angle, milliradians are just the metric version of minutes. And, of course, when it comes to laser rangefinders, smaller is better. Some manufacturers report beam divergence as a rectangular shape, as in the Leica CRF 2800B: Vertical – 1.28 x Horizontal – 0.85 milliradians. Others report numbers which suggest a circular shape, as in the Leupold RX 2800: 1.172 milliradians.
So, how much divergence is this really at distance? To make it simple, let’s assume a round beam with a divergence of 1.2 milliradians (which converts to 0.068755 degrees, if you prefer). The metric system makes the math easy because one milliradian is exactly one metre wide at 1,000 metres, meaning our beam is 1.2 metres wide (47.24 inches) at 1,000 metres (1,094 yards.) Most people don’t realize their rangefinder’s beam is about four feet wide at that extended distance.
Reticle & Beam Alignment
While I don’t know of any method for consumers to test beam divergence, we can test a rangefinder to determine if the reticle and the beam are properly aligned. Sometimes they aren’t and if that’s the case, you’ll miss ranging a target just as surely as you’ll miss a rifle shot if your riflescope isn’t zeroed. This is a test I’ve seen rangefinders fail, making it an important evaluation to run on every rangefinding device you own.
All rangefinders have a reticle which must be superimposed on the target when the ranging button is activated. In a properly aligned device, the laser beam will strike in the centre of that reticle. But as we all know, no company’s quality control is perfect and even if a device leaves the factory properly aligned, there’s no guarantee it’ll stay that way. This makes it prudent to check your rangefinder at the start of every season. Fortunately, it’s also easy, and can be done at the range the same day you’re sighting in your rifle. The only hard part is the necessity to hold your rangefinder extremely still while ranging. Mounting it on a tripod is one of the best ways to do that. Another option is to stack up some sandbags, wedging it in tight while leaving enough room to operate the controls.
Start by ranging either a large steel target or the target backer at the 100-metre line and noting the distance. Then move the reticle to the top of the target and range the top edge several times, pushing the reticle closer to being off the edge each time. As you break over the edge, you should see the distance reading change to reflect the distance to the berm, or whatever else is behind the target. You’ll recognize a problem if, for example, the reticle is off the target and the distance to the target is still what’s being displayed. This tells you the beam is striking below the reticle.
After testing on the top edge of the target, run the same test on the bottom edge. Then left and right edges as well. If your range has 200 or 300-metre target frames, consider checking at one of those distances as well. Hopefully, the results will all be good. If they aren’t, your best alternative is to contact the manufacturer for assistance in repair or replacement. If you can’t get the necessary service, it’s possible to simply adjust your point of measurement on a target animal to compensate for the error in beam/reticle alignment.
Rangefinder users often assume their instruments will work equally well in all conditions and on all targets. I wish it were so, but several factors influence how well a rangefinder can read a distant target. It breaks down like this: white targets are better than black, targets at right angles to the beam reflect best, large targets can be ranged further than small ones, cloudy days are better than sunny ones, and clear days will yield better results than hazy, humid or smoky days. Naturally, when manufacturers publish how far away their products will read distances, they use ideal targets in ideal conditions. Beyond these factors, a fresh battery will often fix everything that’s wrong with a rangefinder, as will cleaning all the lenses; both of these last two items are often overlooked when troubleshooting a rangefinder.
Fortunately, the lasers we use in the hunting and shooting sports are extremely safe. In the world of lasers, they are low powered and there’s no risk of cutting or burning anything with one of these beams. They are classified as “relatively eye-safe.” However, we should never, ever point any of the laser-equipped gear we use at a person. It’s not worth the risk.
In my opinion, the laser rangefinder has been the greatest asset developed for rifle shooters in modern times. And with laser development continuing at a feverish pace, I’m sure we have more laser-powered products to look forward to. Science fiction could even become reality and we might see the laser firing rifle in our day.
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