Laser Ranging

Over the past decade I've used nine different laser rangefinders—and owned four—from three different manufacturers. I've field-tested them from the Arizona desert to the mountains of Alaska, the rarified air of the Rockies, and the forested mountains of Eastern Europe. Though lasers seem to be as temperamental an instrument as ever devised by man—you can range to 750 yards with one rated to 600, but cannot get 500 yards out of one rated for 800— I think I've finally figured them out.

I can thank Bushnell's top laser engineer, Tim Carpenter, for educating me along the way. He explained that a rangefinder uses a laser diode similar to a pen pointer, except it emits pulses of nonvisible wavelength light. Bushnell lasers, for example, have a wavelength of 905 nanometers (nm) in the infrared spectrum, while visible wavelength light measures 400 to 700 nm.

The laser diode emits light pulses of about 34-45 nanoseconds, which illuminate and reflect off a target, and this is optically detected by the rangefinder. This tiny reflection is amplified, then registered in multiple circuits containing a high-speed chronometer that measures the time it took for the light to reflect back. This time is converted to a distance, which appears in the device's liquid crystal display. Bushnell lasers are calibrated to read +/-1 yard of a lazed target.

interestingly, Carpenter explained, a laser rangefinder's maximum range is not determined by the laser's output. In fact, all Bushnell lasers—whether 600, 800, 1,000, or the latest 1,500-yard device—employ the same strength laser light emitter. The device's maximum effective range is determined by the quality of its receiver and its ability to measure milliseconds and sense tiny light reflections. The difference between economical units like Bushnell's and more expensive models also reflects lens quality and the ruggedness of construction. (Plus, the high-end lasers are installed in a pair of top-quality binoculars.)

Range and Wind Estimation

Range and Wind Estimation

View through the author's Bushnell Yardage Pro 1000 laser rangefinder, which measures in meters or yards.

Though Bushnell lasers use high-impact plastic rather than metal cases, it's worth noting that this also makes them lighter and more compact than the more expensive models. I guess it comes down to preference and pocketbook.

Interestingly, tests at Bushnell have revealed that scratched or dirty lenses do not degrade laser performance much.

Perhaps the least understood part of laser ranging is properly matching the beam's size to the object you're ranging. Many snipers don't get the maximum range out of their rangefinders because they imagine this beam is the size of a laser pointer beam. Wrong! Bushnell laser beams, for example, are 4 mils high and 2 mils wide. The closer your target is to these dimensions, the greater the likelihood that the beam will reflect off it to yield a range. For instance, at 500 yards this means a target 2 yards high and 1 yard wide, and double these dimensions at 1,000 yards. Thus, instead of ranging on a thin human—who's not even half the size of your beam—laze a wall 25 yards to his side, hopefully perpendicular to your beam.

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