What is the function of the infrared camera lens?

Since the infrared thermal imager can change the surface temperature of an object that is invisible to the naked eye into a thermal image that can be directly seen Therefore, infrared thermal imaging cameras are widely used in the detection of latent thermal hazards such as electronic or mechanical equipment. So, what is the mystery hidden in the infrared camera lens? How is the temperature converted into a thermal image? The infrared camera lens is made of germanium and other materials or other materials with low absorptivity and reflectivity in the infrared spectrum. But why use these special ingredients instead of more common substances like glass? Infrared thermal imaging cameras work differently from ordinary visible light cameras. The function of an ordinary camera is more or less the same as the human eye, receiving radiation in the visible spectrum and converting it into an image. However, thermal imaging cameras use heat (ie infrared or thermal radiation) instead of visible light to take images. The performance of infrared radiation is quite different from that of visible light. Therefore, the lens of the thermal imaging camera needs to be made of materials different from ordinary cameras. In the visible world, the properties of a particular material may have nothing to do with its properties in the infrared world. For example, glass is extremely transparent to radiation in the visible spectrum, but in the infrared world, long-wave infrared (8-14uM), glass is completely opaque. Vice versa, germanium is a semi-metallic element similar to silicon, which is completely opaque in the visible world. But in the infrared world, it is a substance with high transmittance. Because of this, the lens of the FLIR thermal imaging camera is made of germanium or other materials that are almost transparent in the infrared spectrum. In order to facilitate the conversion of thermal radiation into thermal images So the lens of the thermal imaging camera is made of germanium