Thermal imaging?

Hi!

I'm just wondering.. So thermal imaging/IR thermal imaging today uses a microbolometer - but is there any form of film for thermal imaging available? Or something that used to be available? I mean, according to about.com, the technology was invented a long time ago..

I know there is infrared film - but according to wikipedia:

IR film is sensitive to infrared (IR) radiation in the 250°C to 500°C range, while the range of thermography is approximately -50°C to over 2,000°C. So, for an IR film to show something, it must be over 250°C or be reflecting infrared radiation from something that is at least that hot. Night vision infrared devices image in the near-infrared, just beyond the visual spectrum, and can see emitted or reflected near-infrared in complete visual darkness. Starlight-type night vision devices generally only magnify ambient light.

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Film that's not sensitive to visible light but to temperature (infrared ratiation with wavelengths between 8-13 μm) should be shielded with liquid nitrogen before and after exposure? Or would it have to be developed instantly after exposure?

And, what is this all about?

Again: i'm just playing with the idea! Please don't come tell me it doesn't exist and that i should just forgetaboutit.

Well, people have done Schlieren photography with ordinary film for some time, and with that you can see thermal signatures from matches and bodies and such. But it is not direct thermal imaging.

What photographers call infrared is what the scientific world calls near-infrared or even extended red or visible-edge infrared. Most IR films have little sensitivity beyond ~900nm and you really don't start seeing heat signatures until 2 microns or so. A digicam, with hot mirror removed, can see to ~1200 and can thus image some things thermally, but those sensors still are a far cry from true thermal imaging sensors.

Direct thermal imaging is something most now do by FLIR (forward-looking infrared) with carefully calibrated sensors... not with film. FLIR can go way out to several microns (I have 5-6 microns in my head, not sure about that though). At those wavelengths you can see heat reradiated from the earth.

In principle it might be possible to do some thermal imaging very slowly with film, but then you are fighting directly against fog, and the contrast will suck. Fog is a thermally driven process. So you'd be trying to make a fog image, in essence.

But check out Schlieren, a creative mind can do all sorts of things with it.

P.S. Okay, just checked good old wikipedia, there ar enow long wave IR imaging systems that can see out past 12 microns. Pretty incredible.

http://en.wikipedia.org/wiki/Forward_looking_infrared

of course, in the near infrared a CMOS sensor in a DSLR is IR sensitive except they block the IR with a filter. With a large format scan back, you must expose through the IR blocking filter but you may also use a visible blocking filter to use this near IR instead of film.

wow! http://www.youtube.com/watch?v=lSFwH0BVd3Q

thanks alot for the tip! (although it's rather difficult to use this technique for.. well, photographing heat leakage in a house for example..)

i want to try this sometime!

I believe a true IR sensitive film would simply expose and fog itself due to black body law.