The night vision scope and thermal imager operate using the same IR range, but different wavelengths. The night vision scope is fundamentally not that much different from a conventional telescopic sight, it simply features a light amplifying element called an image intensifier.
Therefore, we see the actual image in the eyepiece, just as in a regular scope. This is also the reason why a night vision scope without illumination is useless in total darkness. There is simply nothing to intensify.
The principle on which a thermal imager operates is somewhat different: the infrared gets through the lens and hits the sensor operated by microbolometers. The sensor data is then processed and fed to the screen. Lighting does not matter for the thermal imager, as it picks up temperature differences between objects.
In our new video, Kalashnikov expert Yevgeniy Spiridonov talks in-depth about the right way to use these devices in limited visibility conditions and the new opportunities they offer to a modern hunter.