What is the difference between a thermal Infrared imaging camera and CMOS Night vision cameras?

2019-07-26

There are some other great answers here, but I thought an answer that focused on the difficulties of making a thermal imaging camera as opposed to night vision camera would be entertaining:

Thermal cameras use radiation from in the far infrared region of the spectrum, while IR night vision cameras use light in from the much higher frequency range of near infrared region. They may both seem like minor variants of “infrared” to the uninitiated but differences in the spectral ranges are very different: the range of wavelengths for the near infrared is 0.75–1.4 um (micrometers) while the the thermal imaging range is 8–15 um. Each of the those range covers about an octave, but they are separated by over 2 octaves. In contrast, the near IR range and the visible light range are right next to each other. Thus, the near IR range has more in common visible light than it does with the thermal imaging range. (I know, “octave” is usually a music term, but it is handy in this case to mean the high end of a range is twice the low end.)

Thermal imaging image is forming from infrared radiation of target, which has a strong penetrating ability to through the smoke, but image details are not as goods as CMOS.

The CMOS image is rich in content and the texture is clear, but the image quality will be seriously affected when the lighting conditions are poor.

From an engineering point of view these frequency ranges are very different: For example one can use regular old glass and regular old silicon sensors in a near infrared camera. (In fact cheap cameras for visible light are by default even more sensitive to near infrared radiation. All you have to do to make such a camera into a near IR camera is to slap an appropriate filter in front of the lens.) But glass is mostly opaque to the thermal imaging frequencies, and silicon sensors don’t respond to photons of that energy. The optics in a thermal imaging camera need to be either mirrors, or if refractive components are used, exotic crystals like those of zinc selenide, germanium, or even cesium iodide. (Basically all the atoms have to be heavy so their chemical bond vibrations frequencies are below that of the thermal range.)

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