[kragen]

prolly not for room temperature; planck's law tells us there's a rapid exponential dropoff of spectral radiance with f/T, and room temperature is about a third of the draper-point temperature, so you'd expect undetectably low radiance below about 2000 nm, three times the 700-nm limit of visible light

silicon's bandgap of 1.1 electron volts corresponds to about a 1100-nm wavelength; is that the minimum photon energy a cmos sensor can detect?

if i did this calculation right, the spectral radiance at 1100nm should be a couple million times dimmer than the 700nm radiance at the draper point

        You have: h c / boltzmann 700 nm 300 K
        You want:
                Definition: 68.513185
        You have: h c / boltzmann 2000 nm 300 K
        You want:
                Definition: 23.979615
        You have: h c / boltzmann 700 nm tempC(525)
        You want:
                Definition: 25.751996
        You have: h c / boltzmann 1100 nm 300 K
        You want:
                Definition: 43.599299
        You have: exp(43.6-25.8)
        You want:
                Definition: 53757836

11³/7³ is about 4 and 54/4 is 'a couple' to me

so it's not literally impossible to detect but it seems like you would probably need special conditions like a light-tight darkroom or a thermal emitter switching on and off at a particular known frequency for millions of cycles

[blincoln]

Yes. In my experience, the scenarios where NIR picks up a difference due to heat are very limited. Years ago, I did a test and there was no visible difference with an electric stovetop until it was set to medium[1], which would be more than enough to severely burn your skin.

A physicist once emailed me to say that it's possible to pick up NIR emissions from a soldering iron, but only in a dark room.

Beyond the sensor limitations, MWIR and LWIR require special optics, because regular glass is opaque to them. The last time I looked into it, the glass was usually germanium-based.

One can do some neat stuff with actual thermal imaging. I was lucky enough to get a FLIR E4 when they could have the firmware replaced to turn them into an E8. 320x240 resolution is still pretty low, but having seen the difference between that and the stock 160x120, I'd not want to use a sensor with a resolution any lower than 320x240 or so.

[1] Scroll way down to the "Stovetop Bokeh (Stove on Medium-High)" section of https://www.beneaththewaves.net/Photography/Thermal_versus_N...

[kragen]

there are a lot of different optical materials you can use, but some of the cheap ones are deliquescent, which can be a real drawback

or you can use mirrors