Contrasting heat signatures on a man and recently shot boar seen through a thermal imaging monocular

Thermal Weapon Sights—A Primer

Written by Pro Staffer Jay S. Idriss, P.E.

Why do you Need a Thermal Weapon Sight?

If you’re like me you spend a lot of resources—both time and monetary—getting your outdoor sanctuary ready for deer season.  Whether your special escape is a lease with a few of your hunting buddies, a public spot off the beaten path, or even a family ranch, the preparation you’ve put in—the countless hours of animal observation, feeding, road trips, game census, deer stand placement and construction—you’re committed.

Thermal image of two deer.
Hunting in complete darkness compromises your depth perception. Judging distances, especially away from known landmarks, can be a challenge. Pictured here are two does being scanned through the Pulsar Trail LRF XP50. Photo by Jay Idriss.

You’re sitting out on opening day right before first shooting light and you see movement. In those next 10 minutes of dawn, you realize in horror—critters.  Hogs. Raccoons. Everything.  Everything is eating and rooting-up your corn and food plot except for the deer!  Here in South Texas, there’s one thing we know—big pigs and big deer do not get along, and unfortunately, we have a problem with the former.

If you’re reading this article, it’s because you have an interest in thermal scopes—thermographic cameras affixed to your weapon which function as optical sights.  These cameras operate roughly between the 3 to 14-nanometer wavelengths of light; the medium to long-length infrared.

Pest control for wildlife management, protecting crops and farmland, and even daytime game observation are the biggest reasons why hunters venture into the wavelengths of infrared.  But before you do, you need to become familiar with some of the definitions and industry terms.  Once you start shopping for thermal, the numbers will be coming hard and fast and preparation will save you time and money.

Resolution, Pixel Pitch and Frame Rate

View of hog targets through a thermal riflescope
Even in open fields, identification from a distance can be challenging. In dense vegetation cover or fog, you will be surprised what is visible through a good, thermal weapon sight! Photo by Jay Idriss.

Technology evolves at an exponential rate—and that’s not a euphemism. The observational projection, Moore’s law, states that the number of transistors in a dense integrated circuit doubles approximately every two years.  Quite simply, the electronic components that are responsible for all that fancy image processing you see when you use a digital camera are shrinking every year exponentially. This means you get more powerful components to fit in smaller, lighter packages and the cost for you is driven further down.

Resolution and Zoom

A pixel is the smallest part of an image represented on a screen. The more pixels you have, the more detail your image possesses. With thermal sights, the resolution of the infrared array detectors is paramount. 320×240 models are available on the lower end, with 640×480 models being available and highly recommended if your budget allows. Ten years ago, you would be spending new-car money for a 640 sensor. They’re relatively affordable now.

Again, one nuance about detector resolution is just that—it’s a detector and it’s producing a digital image. We’re not talking simple display resolution here, we’re talking digital data resolution.  You can only interpolate between data—you can’t get data you don’t have.  For this reason, the higher resolution detectors allow greater digital zoom in operation.

Man looking through a thermal riflescope while hog hunting
Being able to scan your surroundings without sweeping a weapon over unintended targets is paramount to safe and efficient hunting, target acquisition and identification. Photo by Jay Idriss.

If you’re looking for a scope that will give you a large field of view with low magnification but want the flexibility to zoom in on targets 200 yards away with decent clarity, a 640×480 model is highly recommended.  At a digital zoom of 2X, you’ll be looking at, essentially, a 320×240 image.  Not only that, but the detection range of your thermal sight is directly related to how many pixels there are in its sensor array.  With a 640 unit, you can detect thermal targets further away with a larger angular field of view.  Sure, recent technological advancements in pixel pitch have resulted in excellent images using 320 cores, but 640 is, by and large, still king for clarity.

Pixel Pitch—Micrometers (microns, or μm)

The size of each pixel, the pixel pitch, is typically reported by manufacturers in units of microns. A micron is one-thousandth of a millimeter. With decreasing pixel size, the number of pixels per unit area increases to provide higher-resolution images and sharper, further-range detection!

Current pixel pitches are anywhere from 24 μm all the way down to 12 μm. Popular offerings from Pulsar have pitches of 17 μm, for example.  In general, the smaller the pixel pitch, the sharper the image due to higher pixel density for a given resolution.

If anyone is keeping score on pixel pitch—it’s nature. Small pixels are inherently less sensitive as there is a finite ‘waste’ from separation and support structure that have a negative influence on detector efficiency.  This can be improved with better low-noise circuitry and better vacuum housings for the electronics, but that conflicts with a desire for simpler and robust packaging, especially for field purposes.  Once the pixel size is reduced to the wavelength size of the light in which you are interested in observing, you are now basically designing an antenna structure and not a simple black body thermistor assembly as before.  For reference, long-wave infrared is in the 8 μm to 12 μm range of light.  We may soon be reaching the efficient micron limit for thermals!

Frame Rate

This one is easy. Do you shoot at moving targets? No?  Ok, you need to come down to Texas and get acquainted with our hog problem!  But I digress…

Contrasting heat signatures on a man and recently shot boar seen through a thermal imaging monocular
Varying color pallets can give detailed contrast to your image in the field. This is through the Pulsar Helion XP50. Photo by Jay Idriss.

Surely you observe dynamic targets and you can be assured that with a higher frame rate, you will suffer less blurry and choppy images. The rate is typically reported in frames per second (fps)—the speed at which the image processor displays a single captured frame on the screen within the viewfinder.  Like resolution, the cost of components has dropped in recent years and 50 to 60 fps units are available.  For the budget-minded, 30 fps are out there and are a bargain.  However, know what you’re getting. If you will be using your sight in a highly dynamic environment, 50 to 60 fps is recommended.

Power Hungry Devices in the Field

As hunters, the only battery changes we usually worry about in the field are for our flashlights or headlamps (… and in our deer feeders too, I suppose).  As more technology is introduced into our field loadout, we find ourselves thinking about button batteries in our red dot sights and illuminated reticles in our riflescopes.  While those batteries aren’t something you may change regularly, a thermal weapon sight should be considered a large powerful digital camera mounted to your firearm or hanging around your neck.  Don’t cut your time in the field short.  Battery life for thermal sights is a concern and some manufacturers have managed the issue better than others.

Pulsar thermal scope, rechargeable battery pack and deer antler
Pulsar’s battery packs are offered in sizes ranging from 5.2 to 10 aH. Photo by Jay Idriss.

Some manufacturers offer waterproof rechargeable battery packs that connect directly to the scope body and provide instant, replaceable power in the field.  In addition, external USB-connected battery packs will power most thermal scopes.  Before deciding on a scope, be sure to investigate what power options are available. There’s nothing worse than having equipment fail or be inoperable in the field when you need it most!

Bells and Whistles—Image Capture, Video Recording, and Wi-Fi Streaming

In my opinion, weapon sights and optical enhancements are tools; we use them to observe, engage, and track.  However, I would be remiss if I didn’t mention some very interesting and useful features that may influence your hunt for the perfect thermal.

Live streaming ad for Pulsar's thermal scopes.
Pulsar’s Stream Vision smartphone app represents the next level in the video-recording arena.

Have you ever wanted to share your hunt or observations in the field with your buddies back at hunting camp?  That question is highly rhetorical—of course you have!  Half of the excitement and intrigue during those late nights at camp results from the epic stories you share among your friends of the day’s and night’s events. To enhance those experiences, most thermal scopes allow you to take snapshots in the field, just like using a camera!

Many thermal scopes also allow you to record video and some offer a recoil-activated pre-trigger—a time window that is selected so that when you fire a shot, a pre-set amount of time prior to recoil is recorded. Videos can typically be downloaded directly to your smartphone or computer.  When you share that video to show the skeptics in your hunting camp that the elusive management buck you’ve been hunting which only shows up past dark, is, in fact, real or you share videos of your hog hunts on YouTube, you’ll be happy you have this feature!

Some thermal sights require the use of an external digital video recorder (DVR) to record video, as they do not have the recording hardware on board.  DVRs are typically attached to your rifle stock in a pouch and connected to the sight with a cable.  Keep this factor in mind if video recording is a feature on your shopping list.

The features go even deeper.  Some Pulsar products allow you to live-stream video directly to a cell phone and live broadcast your hunts to YouTube directly from the field using the scope-created Wi-Fi network. What a time to be alive!

Why not Night Vision?

Green night vision image compared to a black and white thermal image. Thermal image is much more clear.
Note the difference in night vision (left) and thermal (right.) Night vision is an extremely useful tool; but in some situations, thermal is king. Photo by Jay Idriss.

Night vision and the affordable subset of digital night vision that detects reflected infrared light from external emitters is an option.  But for hunting, thermal takes you to another level.  Not only do thermal weapon sights work during the day to locate targets through vegetation and in naturally camouflaged environments, they also work well through dust, light fog and rain, and further than most night vision.

On a recent predator hunt, it was overcast, with some moon.  Night vision would have been better than the high-powered red LEDs my spotter and I used, but due to the dense cover, a thermal weapon sight was ideal.

Information Overload—Which Thermal Should You Buy?

By now, your head is spinning with specifications. Which features do I pick? How far will I be shooting? What is my budget?  Only you know which features are most important for your situation. Here are my top three high-end thermal weapon sights:

Pulsar Trail XP50

thermal riflescope mounted to an AR-15

This is Pulsar’s flagship thermal weapon sight, and my current top pick.  At a street price of around $5,000, the Trail XP50 gives you excellent image quality with a 17 μm pixel pitch at 640×480 resolution with 50 fps refresh rate, innovative picture-in-picture zoom features, onboard video recording, and great battery life! Pulsar’s new return-to-zero mounts are top notch, as well.

Click here to learn more about the Trail.

Pulsar Trail LRF XP50

Soon to be released are the laser range finding (LRF) versions of the Trail sights.  These sights are identical to the existing Trail thermal weapon sights, but with the addition of an onboard laser rangefinder. To aid with nighttime depth perception, being able to range a target in total darkness with the Trail LRF has proven to be one of my favorite features!

Click here to learn more about the Trail LRF.

Pulsar Helion XP50

A thermal spotting monocular is a mandatory item in my kit for night hunting.  The favorite that I personally own is the Helion XP50.  Pulsar’s Helion series of top-end monoculars are intended for hand-held use. They are compact, lightweight, and have very fine objective lens focus adjustment to allow for stunning target acquisition both near and far.

As your time in the field will most likely be disproportionally monopolized by scanning, the convenience of a hand-held spotter decoupled from your weapon is paramount.  If you are on a budget, using a quick-detach mount to decouple your thermal sight from your weapon is a possibility.  However, especially when hunting in teams, I prefer a dedicated spotter.  Furthermore, depending on conditions and your intended use, the varying color pallets of the Helion series monoculars allow for very detailed identification and close-up images.  The focal range of the Helion XP50 is excellent; even with the large objective lens!

Click here to learn more about the Helion.

Bottom Line

Again, what a time to be alive!  You can go to your favorite vendor; whether it be your local gun store or online establishment, and purchase thermal technology for less than $10,000 right now. Whether you pick a flagship model, a dedicated lower-budget spotting scope, or even a mid-range model, there are weapon sights and spotters to fit every budget.  If you consider the features and specifications outlined in this article when you purchase, you’ll know what you are getting going in and your next hunt in low, or no light may be some of the most fun you’ve had in a while.

Jay Idriss is an avid hunter, conservationist, backpacker, and firearms enthusiast. His favorite game is whitetail deer, and he enjoys using suppressors and other NFA items in his field kit. He coordinates the Wildlife Management Program on the 2300-acre Box Canyon Ranch in Kinney County, Texas and assists with protecting livestock and crops through predator and feral hog control at Golden Meadows; a 2600-acre family Beefmaster and Brahman cattle ranch in Cotulla, Texas. In addition to being an outdoorsman, he is a scientist and licensed practicing professional engineer. His technical practice and research focus on blast-resistant structural design for both anti-terrorism applications and accidental explosions. Mr. Idriss has proudly provided engineering, design, and analytical services to the military related to weapons effects, personnel protection, and survivability for over a decade. Mr. Idriss received his undergraduate and graduate engineering degrees from Texas A&M University.
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