I have a FLIR One IR camera. Works fantastic, but it does top out at 100ºC.

Are there filters available that filter a set amount of IR energy to effectively shift the range of sensitivity?

I.e. could I find some bit of material that would, say, subtract 200ºC from the range, effectively shifting the FLIR's range to 200ºC-300ºC?

  • 2
    You need to dig into the physics behind black body radiation and the wavelength various things are emitting at for various temperatures. I'm fairly sure you've got some mistaken conceptions (that aren't photography). – user13451 Nov 17 '15 at 4:34
  • @MichaelT Thanks. Not mistaken; completely unknown. Thanks for the links. – bbum Nov 17 '15 at 16:03
  • What you are photographing with a camera is the near ir. This is the light reflected by the sun off the surface. Live vegetation reflects it well, dead vegetation doesn't (even if they are at the same temperature). Thermography is in the 900 nm to 14,000 nm range (standard camera sensitivity drops off just below 800 nm). The 800 to 900 nm range is about as significant as blue to yellow (very rough approximation). – user13451 Nov 17 '15 at 16:14
  • @user13451 The FLIR One -is- a 'thermographic' imager... It has a scene temperature range of -20° to 120°C. – BobT Sep 12 '16 at 22:29

Use an IR ND. https://tiffen.com/neutral-density/#irnd An ND Filter for IR.

FLIR's answer: http://www.flir.com/cvs/cores/knowledgebase/index.cfm?CFTREEITEMKEY=914&view=71765 .

Their suggestion: https://www.spectrogon.com/product-services/optical-filters/spectrogon-ab/neutral-density-filters/ .

The first one causes a 50% loss.

  • Finally, the correct answer, except for the tiffen link, which is near IR and will not work for thermal range. The low cost alternative is simply masking the aperture (piece of paper + small hole). – szulat Mar 12 '17 at 9:42
  • The context of the question is that he has added a Lepton Sensor to his Cellphone. The Tiffen Link is more of a simple Tutorial though their HMIRND.9 may suit someone not wanting to pay more for a Filter than they did for their Camera; it would cut visible the most and LWIR the least (10%). EO charges over $300 for a 1" Filter: edmundoptics.com/optics/infrared-optics/… . I've not seen the 'pinhole camera lens' option offered by IR Filter Companies. – Rob Mar 13 '17 at 1:03

No. A filter can only block certain wavelengths, and can't do anything about wavelengths that are blocked/ignored by the camera. All you can do with a filter is to narrow the range of wavelengths captured.

  • Ah-- right-- the temperature of the object determines the frequency of IR emitted. Thus, I'd need to shift frequencies, which can't be done. – bbum Nov 16 '15 at 23:24
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    the answer is wrong, because the question is not about shifting the frequency but about increasing the max temperature. while it is true that increasing the temperature changes wavelengths, FLIR does not care about wavelenths at all, it only knows the total amount of energy received – szulat Nov 17 '15 at 0:10
  • @szulat That it is only sensitive to the total amount of energy received implies that a filter is possible, right? – bbum Nov 17 '15 at 16:03
  • @bbum yes, I think filtering would work, but people at Physics stack exchange might know better. you can experiment with plastic bags, most of them are semitransparent for thermal radiation. – szulat Nov 17 '15 at 19:35
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    @AndyBlankertz they overlay the visible light image but that's only a visual aid and does not influence the thermal readings and temperature range. you can also operate it in a complete darkness where visual image is just black. wavelength matters - the sensor is only sensitive in a certain range - but increasing the body temperature increases the amount of energy in all ranges, including the one that FLIR can receive. – szulat Nov 17 '15 at 23:44

Maybe. The product that selectively blocks a specific defined range of EM (electromagnetic) radiation is referred to as a "notch" filter. They are made from various materials including quartz, germanium, and glass among other substrates and materials. Hit the optical catalogs to locate the likely stuff you want.

Here's a bit of related arm-waving.

As it turns out, all the sensors used in DSLR cameras are sensitive to Infrared regions of the EM spectrum. For that reason, every camera has an IR blocking filter covering the sensor. Removing the filter (theoretically, Don't do it yourself to any equipment you value.) will give you an IR camera. Some after-market places will remove the filter, professionally, with a warranted guarantee.

Silver halide film emulsions are naturally sensitive to ultraviolet radiation. Thus, UV filters became 'de rigeur' for serious photographers to kill the unwanted extra non-image forming radiation. They were also called "haze" filters. Atmospheric haze affects DSLR sensors less that it does to silver halide emulsions. Nowadays, putting an uncoated piece of glass on a DSLR lens will give the same amount of physical 'lens protection' as an 'unnecessary' filter.

My arms are tired.

While filters cannot add missing radiation, they alter the relative amounts of wavelengths in the rendering to give the appearance desired such as a colour "shift." That's what filters do pictorially.

To shift a rendering a desired amount in a desired chromatic direction try the so-called "colour correcting" and "colour balancing" filters.

Furthermore, a system has been developed (!) to alter photographic rendition by a known amount of hue. The mired-shift (usually measured in deca-mireds, practically speaking) can be very accurately altered by known amounts after you calibrate your filters into either red or blue equivalents. A mired is the inverse of the correlated colour temperature x 1,000,000. Tables and charts of mired equivalent values are available for existing filters in other designations such as letters and number-letter combinations.

  • OP requested information on "effectively." Evidently, the word I used, "appearance," confused someone. Note that a dictionary is still a handy tool to have around when trying to understand some things. Conversely, somebody might be hungry, alone, lonely, or tired and missed the points I tried to make. : ( Oh, there's my bus. – Stan May 16 '16 at 0:19

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