It is not often that we see thermal imagers in use. This is due to the limited availability, high prices, and the low necessity for them. Thermal is normally employed in one of four forms. Head mounted, hand held, clip on, and as a dedicated sight. All of these have their own pros and cons. Hand held and dedicated sight are what are seen most often, but now clip on thermal optics are being produced and becoming more prevalent . In most cases, thermal optics that are worn on the head like night vision are too bulky and heavy to be practical, but that is changing.
Other then vehicle mounted thermal optics, thermal meant to be used by an individual is mostly seen in the military and in hunting. In the military, a thermal optic mounted on a machine gun will allow that position to quickly spot anyone in their fields of fire. Some hunters use handheld thermal optics to quickly spot game that they would not have seen otherwise. The rule of thumb for night vision that that if you can not see it in the day, your not going to see it at night. However since thermal works differently then night vision, you can see many things with thermal that you would not have seen otherwise. The caveat is that thermal takes more effort to use and is less intuitive then standard night vision.
I’ve found that hunter that work during the night usually prefer to have a hand held thermal device for scanning and finding the game. Once they have spotted something, they use a night vision scope to identify it, and shoot it. Often the reasonably price thermal devices are rather lousy in resolution. A wide field of view combined with a low resolution lets the hunter quickly spot warm blobs, but they can not always tell what what blob is. That is why the standard night vision scope lets them identify their target and get a good clean shot.
The military can afford dedicated thermal optics with higher resolution. While I was in, the primary use of these was to mount on a machine gun in the defense and use the thermal for scanning for enemies attempting to breach the perimeter. These dedicated optics, like the PAS13 shown in the picture above, have some awesome capabilities. I’ve been able to see peoples facial expressions up close, their load bearing equipment and weapons at distance, and in very cold weather, footprints on the ground. However these optics are large, bulky, and eat batteries like a fat kid eats candy. The PAS-13 pictured above gives a great picture, but is still large, mounted very high over the bore, and is slow to use. While a dedicated thermal optic is a great force multiplier in a military squad, for the individual combatant it is slow and awkward.
Now there are two options that are growing in popularity, clip on thermal optics and blended thermal/night vision optics. Clip on thermal lets you mount a thermal optic in front of your already zeroed day optic. If everything works right, you gain thermal capability with out a change in zero. Trijicon offers a clip on thermal sight that is available to the public that is getting rave reviews. The blended (hybrid) optics give you the best of both worlds with thermal and night vision. However these are still huge, and mostly unavailable to the public.
Most thermal sights are just in black and while. These have the option to switch between white representing hot or black. I recommend often switching between white hot and black hot settings as you scan, as sometimes objects will be very recognizable in one, and not the other. Some thermal designed for hunting will have a feature that will tag hot object for tracking and identification. Most will auto-adjust the picture but I have found that if you are in a stationary place, manually adjusting the contract and brightness will give you a better clearer picture. I would not recommend a thermal sight on a precision weapons system as thermal can not see thru glass, often has coarse crosshairs and adjustments, and can be slower to use then most other optics. Also for the warfighter thermal is a force multipler but it can be awkward and slow and thus should not be the lone individual’s primary optics system.
So to sum it up: Thermal is awesome, but bulky and slow. Handheld devices are great for locating heat sources, dedicated thermal optics best for the stationary defender or hunter. The Holy Grail of thermal are the hybrid night vision/thermal optics and the small thermal optics that can be use hand held, clip on in front of day optics, and as a stand alone optic. Expect to pay a good deal should you decide you want a thermal optic.