Buying guide for best thermal monoculars
Thermal monoculars are without a doubt the best of all optical instruments for seeing in the dark. They use a special lens to capture the electromagnetic (infrared) radiation emitted by people, animals, and other warm objects, then a complex digital array creates a heat map, called a thermogram. Thermal monoculars work in absolute darkness, but unlike other kinds of night vision, they also function perfectly well in full daylight.
Thermal monoculars are very popular with hunters, but they have a range of wildlife, surveying, and, of course, tactical military uses. While the principle is pretty straightforward, there is a vast choice available, and the technical aspects can be confusing.
Key considerations
Sensitivity and resolution
One of the biggest areas of confusion with thermal monoculars is image resolution. Entry-level is 240 x 180 pixels, 384 x 288 is common, and 640 x 480 is considered high resolution. Those numbers are much lower than even the most basic camera in a smartphone, but those comparisons are unfair. Anyone expecting 4K or other high-definition images is going to be disappointed.
Sensors: The main reason is the size of the sensors and the data being captured. In a camera, the pixels are just 1 or 2 microns across (1 micron equals 1/1000 millimeter or roughly 0.00004 inch). In a thermal monocular, those sensors are huge by comparison — generally between 12 and 18 microns. This increased size is because the thermal sensor needs to capture many different wavelengths. It captures daylight, just like the camera, but it also captures low-, medium-, and high-frequency waves that are invisible to the human eye. Interpreting those gives you a multitone image showing different amounts of radiation (usually called “heat”) no matter how dark the surroundings are.
You may see higher numbers quoted because display screens themselves can have a higher pixel density, and the software on some will try to create a more precise image. However, with current technology, 640 x 480 is as good as the true resolution gets. Still, that’s perfectly capable of showing you hogs, deer, or people in the darkest of conditions. There isn’t any other device you can buy that will do that.
WiFi capability is great for watching your adventures back at home, but it isn’t much use out in the field if you’re in an area with poor or no coverage.
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Features
Optics
Magnification: This can be anywhere from 1.5x to 50x, depending on the model. It’s either stepped or smooth, and the difference can be dramatic. A stepped magnification jumps from, for example, 2x to 4x in a single leap: it’s one or the other, with nothing in between. Smooth magnification is exactly that throughout the zoom range. Monoculars that offer this tend to be more expensive.
Range: Manufacturers often make a big thing about range, and the numbers can be impressive. Almost all thermal monoculars will exceed 1,000 yards, some several times that. It depends on your purpose, but most people (particularly hunters) don’t need to see a warm object a mile away. More important perhaps is the ability to see precisely what your target is at 50 or 100 yards.
Refresh rate: Unlike an ordinary scope, a thermal monocular isn’t showing you a real-time image, though it might seem like that. What it’s doing is capturing data, working out the heat map, then showing it to you. It all happens very quickly, but refresh rates vary from around 25 hertz up to 60 hertz, which has a major impact on how smooth of an image you see.
Field of view, eye relief, and exit pupil: Those who are used to buying daylight binoculars or monoculars might wonder about things like field of view, eye relief, and exit pupil. This information can usually be found if you dig around for it, but it isn’t widely publicized unless you’re looking for specific rifle scopes, and even then it can be hard to find. We suspect it’s mostly because those features can be valuable in daylight situations, but in the dark, with the focus solely on a warm object, they don’t have quite the impact.
Black and white vs. color
The thermal image itself can be displayed in a number of ways. Black and white is usually the default and often provides as much detail as you need. Other color ranges can provide specific benefits in different ambient light conditions and surroundings. These are selectable at the touch of a button, so you can quickly find which one is best. What you won’t get is full color.
Components
Rangefinder: You’ll usually get a built-in rangefinder, though the accuracy varies.
Digital compass: This is another common addition.
Gyroscope: Any handheld device can suffer from a loss of image clarity as your hand moves, and this is exaggerated by magnification. A gyroscope irons out the worst of the problem.
DID YOU KNOW?
Reptiles and amphibians — frogs, lizards, snakes — are cold-blooded, and as a result, they’re invisible to thermal monoculars!
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Other capabilities
Video: Most, though by no means all, thermal monoculars provide for on-board video recording via SD cards. This is where the comparatively low resolution pays dividends. Much smaller file sizes mean much longer recording times, though you’ll probably still want to check the capacity of the SD card. Many are 8 gigabytes and some are 16 gigabytes.
WiFi: WiFi capability gives you the opportunity to share videos via phone, tablet, or TV or stream to online video sites. Most are Android, iOS, Mac, and Windows compatible, but it’s worth checking before you buy.
Apps: These can add functionality, including the ability to remotely operate your monocular, but feature sets vary enormously, so it’s an area worth looking into.
Hunting
Thermal monoculars for hunters might provide specific ballistic information (wind, elevation, target speed, and so on). Some offer Picatinny rail mounts, though you’ll want to consider weight. If you want something specifically for rifles, a thermal scope is perhaps a better option. Most don’t have as comprehensive a feature set, but they are similar to a standard scope in design.
Batteries
You might expect batteries to be the most straightforward of all the elements, but while some thermal monoculars have rechargeable lithium-ion units built in, a good number still use plain old AA batteries. Carrying a spare set around can be quite bulky!
Durability
If you’re out in all weathers, you’ll want to know that your thermal monocular can survive getting cold and wet. Most manufacturers give you an operating range, and many are functional well below freezing. The Ingress Protection (IP) system is an independent rating for waterproofing, and a number of the devices we looked at achieved the IPX7 standard (details can be found online. If it doesn’t have an IP or IPX rating, it might still be waterproof, but you’re taking the manufacturer’s word for it.
Battery life is seldom what manufacturers claim, and you can bet the batteries will run out when it’s least convenient. It’s always worth carrying spares.
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Thermal monocular prices
Inexpensive: Unfortunately, there’s really no such thing as a cheap thermal monocular, with even entry-level models starting at around $1,500. However, there’s a good choice of very capable devices at this price.
Mid-range: The majority of popular thermal monoculars run from around $2,000 to about $3,500, and we expect most people will find what they need in this group.
Expensive: High-specification models cost $4,500 and up, and they can be as much as $15,000. The latter are designed for static use, with lenses up to 6 inches across.
FAQ
Q. Why are thermal monoculars so much more expensive than night vision goggles?
A. While both use a type of infrared, the underlying technology is quite different. Night vision enhances existing light, but there has to be something for it to work with. Because it intensifies all the available light, night vision goggles can’t be used in daylight. In thermal monoculars, the infrared detect radiant heat — from bodies, warm vehicles, buildings, and so forth. As discussed above, they work in absolute darkness, but they also work perfectly well in daylight. In general, thermal monoculars also have a considerably greater range.
Q. Can a thermal monocular really identify a target at over 1,000 yards in the dark?
A. Yes, but we need to qualify what’s meant by “identify.” Depending on the model, it’s perfectly possible that a thermal monocular will show you a warm body at that distance. In fact, we’ve seen one that had a range of up to 9 miles! However, it can be difficult to tell just what the item is. As the range increases, the clarity decreases. With cheaper scopes, things beyond a couple of hundred yards are likely to be little more than hot blobs! One manufacturer put it well by saying that its model will pick up a “person-sized object” at 2,000 yards. It doesn’t say that you’ll be able to recognize whether it’s a person, a bear, or a hot water tank!
Q. Can thermal monoculars see through solid objects like walls?
A. No. Unfortunately, they don’t work like the technology you see in action movies! They don’t have the ability to penetrate barriers. In fact, thick smoke can be enough to block them. If you have a clear line of sight, they’re great, but they may not find things hidden in dense undergrowth.
