A Realist's Guide to Thermal Optics

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There’s an emotional roller-coaster waiting for anyone thinking about buying a thermal device. The first jolt is astonishment as you see the world through a thermal for the first time. These digital devices turn temperature variation into images, literally seeing into the dark and detecting hidden hogs, deer and your neighbor’s dog.

The second emotion is desire. You’ll want one so badly that you’ll find a way to justify your purchase of a gadget that costs upward of $3,000 or more. Much more.

But ownership has a tang of regret. You’ll realize your investment isn’t quite as optically sharp as you expected, or it’s too complicated to navigate all the menu options, or you’ll have a hard time recruiting buddies to hunt coyotes on cold winter nights.

You’ll sell your thermal, and immediately begin shopping for a new, more advanced model, if only to get back on that escalator of excitement and nocturnal discovery.

Military to Mainstream

Welcome to the new and exhilarating world of thermal optics. Just a couple years ago, thermal viewers, riflescopes and binoculars were exotic playthings of just a handful of hunters, mainly veterans who had experienced the capabilities of military-grade thermals in theater or those gadget-junkies who are early adopters of trends that never quite catch fire. But in recent years thermals have decidedly caught fire. Every month there’s another brand and product on the market, and the established companies have filled out their product line with devices to fit every budget and use case. It’s possible to spend $8,000 on a consumer-grade thermal scope that can detect targets out to three miles, or $400 on a device the size of an ice cube that connects directly to your phone.

While thermals are mainly used to hunt hogs or predators at night in those states where it’s legal, most states prohibit their use for hunting deer, elk or other game animals. And some states are discussing banning them from the field entirely during hunting seasons. That’s an indication how disruptive this new wave of technology is. If you enter the thermal club, expect to be embraced by fellow technologists and gently ostracized by traditionalists.

I might also observe that thermals have a generational appeal. Most hunters I know under the age of 30 either have a thermal or they’re saving for one. Maybe it’s that younger hunters are digital natives, so the technology and mobile-app connectivity of thermals isn’t intimidating. Maybe it’s because younger hunters don’t have established access or traditions of big-game hunting, so they’re gravitating to coyotes and other animals that don’t have the crazy competition or entitlement that has come to define deer and elk hunting across much of the West. Or maybe these younger hunters are consummate gamers, so seeing the world through pixels and color palettes isn’t as jarring as it is to older hunters who quit hunting at sunset and who define “gaming” as a jolly round of cribbage.

Whatever the reason, it’s high season for thermals, and given that you’re going to encounter them and hear more about them every year, we offer a guide to the technology, the various types of devices within the category, and what you can expect in terms of performance at each price point.

How Do Thermals Work?

Instead of optical glass, thermals use a special material in their objective lenses called germanium, which sounds like something James Bond would fight Soviet villains to obtain. Germanium is a glass-like element that registers variation in temperatures. Thermal devices use the material in their objective lenses, but the beating heart of these instruments is what’s called the thermal core, where the temperature data received by the germanium lens is converted into a digital image, composed of pixels just like on your phone or TV screen, that is then transmitted through a digital display to the users’ eye.

Because the image is digitized almost from the start of this process, it’s easy to record and then share the content. Most thermal devices have the ability to record photos and videos from an outing, and many of them connect to a mobile app that facilitates live-streaming, image transfer and sharing via text, Instagram or whatever digital means you prefer. Most thermals can be operated from your phone, enabling you to change the magnification in scopes or to shoot a video clip through a binocular instantly and remotely.

Because the thermal image is digital, it’s possible to add all sorts of other chicanery. Most thermals allow you to select your reticle from a dozen alternatives, and you can change what’s called the color “palette” to highlight different temperature readings.

So why are thermals so expensive? Just as in traditional optics, much of the price variation stems from their resolution. A traditional German binocular is, generally speaking, more expensive than one sourced in China, because its clearer glass and more sophisticated coatings produce a sharper, more resolved image. Same with thermals, only instead of glass and coatings, resolution is achieved by thermal cores, sensors and displays with more and finer pixels.

You’ll see sensor resolution expressed in microbolometers and display resolution expressed in pixels. A thermal with a 384x288-microbolometer sensor is about half as sharp as one with a 640x512 sensor, which is in turn about half as sharp as a high-end unit with a 1024x1024 sensor. But you’ll pay for this step up in performance. Generally speaking, you can expect to pay double for every two-fold increase in sensitivity, so that 384x288 unit might cost $1,000, the 640x512 unit $2,000, and $4,000 for the 1024x1024 thermal.

But sensor resolution isn’t the sole measure of a thermal’s performance. The display resolution also plays a part. Some brands use low-resolution sensors but high-resolution displays to trick the eye into seeing detail.

Thermal Viewers Vs. Thermal Sights

About half the thermals on the market are simply observational devices. These are often called thermal “viewers,” generally monoculars or binoculars. They aren’t designed to be strapped on a firearm, but instead are hand-held units that have added versatility because they can be used in so many situations. I have a building-contractor buddy who uses his thermal viewer to hunt coyotes at night and to detect faulty wiring behind drywall in his day job, and firefighters employ them to find victims of housefires in smoke-obscured rooms.

I realized early in the thermal coyote game that a hand-held viewer was just as valuable as a gun-mounted sight for its ability to scan the landscape, detect animals, make positive identification and then record the encounter.

Thermal sights, on the other hand, are a category of firearm-mounted devices, either dedicated thermal rifle scopes or “clip-on” thermal units that clamp to the objective bell of a daylight rifle scope, turning it into a thermal scope. Thermal sights generally have reticles, ballistic calculators, many have built-in rangefinders, and some even have recoil-activated video, which saves recorded encounters 30 seconds before you pull the trigger and 30 seconds afterward.

As I mentioned, serious thermal hog and coyote hunters often run both a hand-held viewer and a dedicated weapon sight. But if you have a hard time justifying the cost of a single thermal, you’ll be doubly challenged to afford two. It’s hard to say which is more essential if you’re going to buy just one thermal. A viewer enables you to detect targets, but it’s hard to shoot those targets with a daylight optic. On the other hand, a thermal sight is great for shooting, but lousy for scanning.

Other Considerations

Comparisons between digital cameras and thermal devices are useful. Some photographers just want point-and-shoot simplicity, without a lot of confusing choices, and are satisfied with middling resolution. There are plenty of cameras out there for those casual consumers. But others want to maximize the digital resolution of images, and they want the ability to manually override automatic settings to milk the best out of their camera. There’s a camera – and a thermal – for that crowd, too.

Decide which thermal user you are, because if you’re the former but you buy a pricey thermal, the customizable features are wasted on you. But if you want to push the capabilities of the platform, you’ll be disappointed in the limitations of entry-level units.

Be skeptical of bargain-basement thermals. Many are clones with no brand support, others have such low resolution that they provide just vague suggestions of targets. Have a battery charging plan. In my field testing, on the northern plains of Montana in the winter, I’ve found that most thermal batteries provide only about 70 percent of claimed run time, and that’s with keeping spare batteries in my vest, close to my own thermal core. Also, note that many thermals claim to detect targets at astronomical distances. But detection distance is simply the extent at which the device can register a heat signature. The more useful claim is recognition distance, or the yardage at which the user can determine if the object is a human or an animal. Most thermals also provide their specific “identification range,” the distance users can determine precisely what the object is.

If you’re interested in connecting a thermal with your phone, make sure it has on-board Wi-Fi and Bluetooth. Some units record photos and videos to an on-board SD card, but in order to fetch the footage, you have to connect the thermal to a computer with a cable. Others transmit the content wirelessly to a phone through a mobile app.

Lastly, inquire about a thermal’s warranty coverage. Most traditional daylight optics are covered by transferable lifetime warranties, but thermals have only 2- or 3-year limited warranties. Because of the fragility of the germanium lens, the glitchiness of electronics in the cold, dusty, bumpy world of predator and hog hunting, and the pace of evolution of digital software, make sure your unit has as much repair, replacement or update coverage as possible.

Thermal Units

Starting with the tippy-top of the market, a $7,000 thermal scope, down to a $400 unit the size of a wine cork, here are six thermals that hit every capability and price point.

InfiRay BOLT TX60C

This new thermal scope offers the highest sensor and display resolution on the market. The picture delivered by the Bolt is sharp, vibrant and three-dimensional, a quality lacking in many thermal images. The InfiRay Outdoor scope features a premium 1024x1024 sensor and 2560x2560 display, but it has an intuitive push-and-turn master control and three-button operation that’s easy to use with gloved hands and in the hectic intensity of an incoming coyote. Add recoil-activated video, easy-to-focus objective lens, and an excellent mobile app and the Bolt almost justifies its outlandish cost. $7,000 | infiray.com

Burris BTS35 v3

A decent price on a do-everything thermal scope, the BTS35 v3 has only middling resolution, but it has all the basics: selectable reticles, nine color palettes, picture-in-picture mode, and connects to the Burris Connect app for wirelessly sharing videos and photos. It also ships with a good cantilever rail mount for Picatinny rails. $3,000 | burrisoptics.com

Sightmark Wraith Mini Thermal

This dedicated thermal scope will get you in the predator and hog game with all the features you need for a pretty accessible price. The Wraith has only a 384x288-pixel sensor resolution, but the 1024x768-pixel display maximizes the image. The scope has five color palettes, a 1,400-yard detection range, the choice of 10 different reticles, 1-8x digital zoom and a built-in mount that easily fits most receiver rails. Unfortunately, it doesn’t connect to the excellent StreamVision 2 app that runs most Pulsar thermals (Sightmark is a cousin company to Pulsar). The Wraith records both video and stills, but you’ll need to manually transfer them from the unit. $1,700 | sightmark.com

Pulsar Krypton 2 FXG50

This is one of the few non-European clip-on thermals, and it doubles as a capable hand-held viewer when paired with Pulsar’s sold-separately monocular. The Krypton 2 FXG50 features an excellent 640x480 12-micron sensor, a high-resolution 1920x1080 AMOLED display, 2,500-yard detection range, and a whopping 11-hour battery life, thanks to a backpack battery that clips right to the top of the unit. Pulsar ships the Krypton 2 with a whole series of adapters to fit a wide variety of rifle scopes. It connects to the user-friendly Stream Vision 2 app that allows users to remotely control the device, stream video from the clip-on and easily record and share photos and videos. $4,500 | pulsarnv.com

Liemke Keiler 25.1

This German-made hand-held viewer is durable, capable and on the “affordable” end of the spectrum of quality devices. The 25mm objective lens and 284x288 sensor give it a decent 1,250-meter detection range, but images look very good thanks to a full-size 1024x768-pixel display. The Liemke features fast and intuitive controls thanks to a scroll wheel to easily navigate through functions and a dedicated photo/video button to record sessions. The Keiler connects via Wi-Fi to a very good mobile app that enables users to easily share photos and videos and control the unit from their phone. $2,600 | liemke.com

Xinfrared T2 Pro

This little marvel is a little larger than a sugar cube and costs only about $400, but it’s a fairly decent thermal with a number of color palettes and both video and still image capture capability. It can do so much because it doesn’t have a screen; it uses your mobile phone’s display instead. The unit plugs into your phone’s charging port, and then is controlled by a mobile app. Billed as “the world’s smallest thermal” it has limited use for hunting but will allow users to see what’s out there in the night and is a fun way to determine the capabilities of thermal devices. $400 | xinfrared.com

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