The laser rangefinder is arguably the most significant product introduction to the hunting world since the bolt action rifle over 100 years ago. In the early 90’s Leica introduced the first generation Geovid, a binocular capable to delivering the distance to a target with the touch of a button. This set off a firestorm of product development and for good reason, the most important contributing factor to hunting accuracy is knowing the distance to the target. Prior to the laser rangefinder, even the most well trained snipers could only estimate distance within +/- 20%, so any shot over 250 yards was not much more than a guess. In those days (and I hunted in those days) the most common phrase uttered in crunch time was “hold at the top of his back and see where you hit.” In hind sight I can see how irresponsible and often unethical it was to take a shot with so little certainty of a clean kill, fortunately those days are behind us.
The concept of how a laser rangefinder works is actually very simple, but of course the reality of actually creating a device is far more complicated. In the simplest terms laser rangefinders use a transmitter to send out a pulsed laser light to a target, the laser bounces back off the target and is collected by the receiver. Knowing the speed of light and the time of flight, the internal processor then calculates the distance. The developing engineers refer to the combination of the transmitter and receiving components, along with the software needed to deliver the yardage as the “engine” of the laser rangefinder. All laser rangefinders use what is known as a class 1 eye safe laser light source, the difference in between units is not a reflection of the power of the laser but is direct result of more sophisticated engine components.
Innovation continues to improve the accuracy and reliability of laser rangefinders. The most current models have the ability to emit hundreds to thousands pulses of laser light for every range calculation, weed out the weak signals, and average the results and deliver a precise distance within fractions of a second.
LCD vs LED
Laser rangefinders can be grouped into two categories, the first being transmissive liquid crystal display, commonly known as LCD. Transmissive LCD rangefinders employ a screen in front of the lens. The reticle and all of the resulting data is projected onto this screen with the familiar black letters and numbers. LCD screens are the least expensive way to build a laser rangefinder, but the reticle and data can be very difficult to see in low light situations. Because the LCD screen literally covers the optical system it blocks a dramatic amount of light, rendering them almost useless in those first and last minutes of the day.
The second group of rangefinders employs and LED display in which the reticle and data are projected onto the lens. Because the LED display is projected there is very little loss of total light transmission. LED components are more expensive than LCD but the advantages are dramatic.
Factors affecting performance
There are several factors that can affect a rangefinder’s ability to deliver a range. The first and most prevalent problem is target quality. Given that LRF’s work by measuring reflected light, flat perpendicular reflective surfaces (think street signs) offer the best target imaginable. Irregular surfaces tend to scatter light and dark surfaces can actually absorb light and will seriously diminish the volume of reflected light and can limit a rangefinders maximum capability by as much as 50%. Unfortunately game animal hides tend to fall into the “non-reflective” category, in fact black bears may be impossible to get a reliable reading on during bright light. If this happens, finding an object within close proximity that does deliver a reading is your only option.
Light will travel through a vacuum at a constant speed of 186,282 miles per second, but our atmosphere is not a vacuum. All atmospheric conditions such as humidity, temperature, elevation, dust, pollution, rain, fog and snow will affect a laser rangefinder. Because a laser rangefinder is metering light, the infrared light emitted by the sun interferes with the engines’ ability to record the laser pulses, so don’t expect a laser rangefinder to perform at its best in the middle of a bright sunny summer day.
Keep in mind, the rangefinder is generating distances of each object it strikes and then averaging them to give you an accurate reading. If the engine cannot get enough consistent feedback it will not give you a reading. Imagine trying to shoot a deer standing off hand at 600 yards, bullets would be sprayed all of over the mountain. The same thing happens when you try to hand-hold a rangefinder with no support. Either use a tripod mount or do whatever necessary to steady the rangefinder on the target.
Last Target and Best Target
Some laser rangefinders can be programmed to filter results in one of two basic modes based on field conditions and target priority. When set on “Best Target” mode, the laser rangefinder will deliver the distance to whatever object is delivering the most results. This is the versatile mode for the hunter, and will provide the fastest and most accurate result under most hunting conditions. However if you are hunting in areas with lots of vegetation then “Last Target Priority”, will as the name implies, deliver the distance to the furthest object the laser senses. Learning to quickly program your laser rangefinder between these modes can be a difference maker on a hunt.
LOS vs Angle Compensation
For more than a decade laser rangefinders could only deliver the actual line-of-sight distance to the target. While this was an epic advancement, the shooter still had to understand trigonometry and how to compensate for the up or down angle to the target. With improved engine software many laser rangefinders can also measure the angle of the shot and calculate the true horizontal distance to the target. By working through the menu, the user can choose either a line of sight value with the angle to the target, or the corrected horizontal distance.
While there are still a host of environmental factors that will affect the actual bullet impact, the true horizontal distance will be extremely effective for most hunting calibers on deer size game out to 400 yards. Most companies limit the distance at which their product will deliver angle corrected yardage and for good reason. If you are shooting at any target beyond 500 yards then you will be better served with the line of sight distance, shot angle and true ballistic system that can measure the environmental influences and combine them with a ballistic profile to offer a far more accurate shooting solution.
Each company has a different name for this value, unless you are using rangefinder that offers a ballistic solution, all corrected ranges are the horizontal distance to the target.
All quality laser rangefinders offer a scan mode in which the LRF will continue to update the yardage at least every second and as fast as 4 times per second. Over the years I have come to rely heavily on the scan function to give me as much data as possible in a short amount of time, especially on a moving target. Keep in mind that battery life in LRF’s is generally reported as a volume of readings, so scan mode drains battery life rather quickly.
~ Chris Denham