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IR Photography

IR Photography. Forensic Applications. Digital IR Photography. Most digital imaging chips sensitive to IR light Must remove filter covering chip How to check camera Turn off auto-focus & set camera to bulb at wide aperture

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IR Photography

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  1. IR Photography ForensicApplications

  2. Digital IR Photography • Most digital imaging chips sensitive to IR light • Must remove filter covering chip • How to check camera • Turn off auto-focus & set camera to bulb at wide aperture • In dark room: open shutter, point TV remote control @ lens & press button on remote • If end of remote glows, camera is sensitive to IR radiation • Will be able to convert camera

  3. What do you Need to Know? • Where in the electromagnetic spectrum is the IR region • What part of the IR region is used • What are the sources of IR light • How to interpret filter data • What are the applications • Under what circumstances would you use IR photography

  4. The Electromagnetic Spectrum Using Light to Find Evidence Ultraviolet Region 190-290 290-400 Short wave Long wave Visible Region Infrared Region 400-455 455-492 492-577 577-597 597-622 622-700 >700 Blue Green Yellow Orange Red Violet IR Near IR – NIR ~ 700-1200nm Far IR – FIR > 1200nm

  5. Infrared Light Sources Maglite Digital IR photography typically relies on a NIR light source sun incandescent lamps. Digital camera sensors based on silicon: NOT sensitive to the far (thermal) IR (typically > 3.0µ ) To photograph in the dark Provide proper NIR illumination External NIR-only flash with no filter

  6. Bandpass Filters • Block wavelengths of light from hitting the digital sensor • Allow wavelengths into the camera • Filters have different characteristics

  7. NIR Transmission Spectra For Several Common IR Filters The graphs at right show transmission spectra for several popular filters — the Wratten 89b (R72), 87 and 87c (B+W 093) IR pass filters and the Heliopan 8125 UV/IR cut filter — based on data from Clive Warren's Infrared Photography FAQ and the Heliopan No. 8125 Digital filter page. Note that the 89b (R72) has a sliver of transmissivity in the deep visible red just below the 700 nm visible-infrared boundary. Some refer to it as a "dark red" filter because you can see through it to a very limited extent, but that appellation doesn't give the R72 proper credit for blocking nearly all visible light. The "black" 87-series filters, on the other hand, pass no visible light at all. The R72, 87 and 87c pass progressively less light to the camera's sensor, which itself loses IR sensitivity at ~1200 nm. For all three IR pass filters, peak transmissivities of only 80-90% also contribute to unwelcome light loss in IR work. No wonder, then, that some cameras can handle an R72 but not an 87 or 87c. The Heliopan 8125 "digital" IR/UV cut filter claims to block unwanted NIR and near UV as well, but the spectrum here shows that most of the longwave NIR still gets through. (That's the kind that theoretically reduces saturation.) I haven't been able to detect any benefit from this filter under normal shooting conditions with several different digital cameras.

  8. Predominately a Red Color Photographed

  9. X-Nite Filters

  10. X-NiteCC1 Bandpass: X-NiteBP1

  11. IR Selective Filters BPB BPG BPR

  12. Infrared Blocking / Visual Light Pass Filter

  13. Ultraviolet Pass / Visual Light Blocking Filter

  14. Other Glass Filter Equivalents: Kaya PF4 780nmKaya PF2 830nm Kaya PF1 & PF3a 1000nm Hoya RM72 720nmHoya RM90 900nm Hoya RM100 1000nm M&K #078  780nmM&K #093 830nmM&K #095  850nm M&K 1000 1000nm Wratten 18A 350nmWratten 29 620nmWratten 70 675nmWratten 89B 720nmWratten 88 735nmWratten 88A 750nmWratten 87 795nmWratten 87C 850nmWratten 87B 930nmWratten 87A 1000nm

  15. Forensic IR Applications

  16. Gunshot ResidueBlack t-shirt GSR Particles T-shirt does not absorb Infrared light

  17. IR Photography of GSRThrough Bloodstains Blood Absorbs In the IR GSR Particles

  18. Oblique White Light Fingerprints on Lab Bench top Oblique White Light With IR Filter

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