The thermal imaging lens mainly plays a role of light filtering, allowing only infrared rays of a specific wavelength to pass through.

The materials of the lens are mainly germanium and zinc sulfide, both of which are relatively expensive materials, which affects the price of thermal imaging to a certain extent.

The lenses on the market are 19mm / 25mm / 32mm / 35mm / 42mm / 45mm / 50mm and so on.

If you use it for search, then a smaller lens is more appropriate. Because the larger the lens, the smaller the field of view, the farther away; the smaller the lens, the wider the relatively closer.

If it is a thermal imaging scope, I prefer to use a 45mm lens. Because the distance from the observation target is appropriate, and the lens is not too large. Of course, in general, the larger the lens, the higher the price.