Thermal Imager: Progress Update 4

I have done some more research on the issue described in my previous post, regarding the Field of view of the thermopile. I have learned that, since thermal sensors operate on a different wavelength to visible light ( I believe the MLX90620 thermopile that I have been using operates between 5 and 16 micrometers) conventional optics won’t work. In fact, they will appear black to the thermal sensor. This was likely why the lens I used didn’t work.

However, it turns out that there are lenses available that are specially designed for thermal sensors. The ones I have researched are called Zinc Selenide, or ZnSe lenses. They can be quite inexpensive, like THIS one. I believe I can use one of these to collimate the light going into the thermal sensor.

I am not 100% sure what kind of lens to use, there are several options. The main two are fresnel lenses and plano-convex lenses. There are many diagrams clearly showing the characteristics of these lenses to be found on the internet (I won’t reproduce them here for copyright reasons).

These lenses are often used to collimate beams from lasers, so, in effect, I am doing the reverse. Instead of emitting light, a thermal sensor receives it. This shouldn’t be an issue however, the lens should still work. The main issue will be to collimate the light, rather than focus it to a fixed point, which is something a lot of laser hobbyists want to do (for burning, cutting, etc).