How far can I shoot with a thermal scope? The question is always asked despite the fact that most thermal scope manufacturers have listed the ‘detection range’ on their specification sheet.
The complexity of this question is the difference between the listed ‘detection range’ and the actual shooting distance of various sizes of targets. We cannot simply conclude how far we can shoot all based on the ‘detection range’.
As this topic discusses the relationship between thermal scope and shooting distance, we assume that the effective shooting distance of the gun is far enough. Under this premise, we need to clarify a fundamental principle of shooting with thermal scope first. Let’s take hunting as an example. When you are unsure what animal or whether the target on display is an animal or not, you must never shoot. This is the first point we want to address today: the definition of detecting a hot object is different from only seeing it.
The following two pictures are screenshots of the thermal imaging video. If you shoot a hog, you will only fire when you are 100% sure the target is identifiable as a hog, as you can see from picture 2. However, you will never pull your trigger when there is only a bright spot, and you can’t tell what precisely the spot is (see Picture 1). Therefore, people sometimes get confused that one can never shoot as far as the ‘detection range’ on the specification sheet. In Picture 1, it is called ‘detection range’ when you could only see a bright spot presented. And in Picture 2, it is defined as ‘identification range’ as we can tell what exact animal within the field of view is.
Is it possible to answer the title question after knowing the definition of the identification range of a thermal scope? Negative.
Suppose a person tells you how far the recognition or identification range of his thermal scope is without knowing what the target is. In that case, you’d better ask clearly because the target size is the precondition of all the descriptions of the distance related to the thermal scope. The detection range, the recognition range, and the identification range must be confirmed together with the target size to avoid misunderstanding. Let’s take the following pictures as an example:
Picture 1 shows two rabbits at 20 meters away, and picture 2 shows a herd of cows around 800 meters away. The larger size of your target, the farther the recognition range your scope could get. That means you may not be able to shoot a rabbit-sized target from 200 meters away, but you can shoot a cattle-sized target from 800 meters away.
Now that DRI is mentioned, we will briefly introduce it as a basic knowledge popularization.
“D” represents detection. According to Johnson’s criteria, ‘detect’ means ‘if an object is present or not. When a heat source is different from the background on the screen, and it will disappear from the screen if it is farther away, then the distance is the detection distance of the target.
“R” represents recognition. ‘recognition’ is defined as ‘being able to see what type of object it is. Recognition refers to the distance you can determine an object’s class (human, animal, or vehicle).
“I” represents identification. Identification refers to the distance at which you can differentiate between objects within a class, for example, identifying the type of vehicle (truck, SUV, or car) or whether the human is a soldier or civilian.
You must have realized that a thermal scope’s detection, recognition, and identification distance varies depending on the target size and posture. A detailed description of target size with detection, recognition and identification range will always be helpful than only claiming on the detection range itself.
Focal length and f-number are the two principal parameter descriptions of the lens.
The focal length is easy to find on the specification sheet. The larger the focal length, the smaller the angle of view and the farther you can see. The larger aperture (the lower F value) of the lens, the stronger ability to receive infrared radiation, and the better the final image quality of the device will have.
Let’s make it simple. A 75mm lens is always better than a 50mm lens for long-range shooting. An F/1.0 lens is always better than an F/1.2 lens for better image quality. Take the following pictures as an example:
It is easy to recognize that Picture 1 taken by a device with 75mm f/1.0 lens has a higher magnification(7X) than Picture 2 taken by the device with a 50mmf/1.0 lens (4.5X) without losing any imagery quality.
The larger the area of the thermal radiation projected by the target onto the FPA, the more temperature data it could absorb, the more detailed picture the system could get, and the easier it to distinguish the target. As the target gets further, the area of the target’s thermal radiation projected onto the FPA will become smaller, and the number of pixels covered will decrease. When the amount of the pixel covered by targets on the FPA is equal to the amount of the DRI range, the target distance is equal to the DRI distance.
Under the premise that other factors of the device remain unchanged, the detector’s smaller pixel pitch makes more pixels fit in the FPA. Take a human as an example. The recognition range requires at least 6 pixels, when there are only 6 pixels on the FPA of a 17-micron device, the number of pixels covered on the FPA of a 12-micron device can be more than 8 pixels, so the 12-micron device has a longer recognition distance than the 17-micron device.
After being projected onto the FPA, the energy will be converted into digital signals by the FPGA, and then it comes to a series of signal processing. Then, the display shows the image. The algorithm, the resolution and the size of the display affect the magnification of the image. Finally, the image on the screen is further magnified through the eyepiece and greeted by the eye.
The detection, recognition, and identification distance description must be classified based on the size and posture of the target you are aiming. It is difficult to tell how far a thermal scope can shoot concisely with only a single parameter. Therefore, when shooting with a thermal scope, please fully understand your targets before pulling the trigger.
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