IR Photography by wanghonghx

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									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
     – 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
  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
    The Electromagnetic Spectrum
                     Using Light to Find Evidence

Ultraviolet Region
190-290   290-400
 Short     Long
 wave      wave

Visible Region                                                    Infrared Region
400-455    455-492    492-577   577-597    597-622      622-700      >700
 Violet      Blue       Green     Yellow       Orange    Red
                                                                       IR




                  Near IR – NIR ~ 700-1200nm
                  Far IR – FIR > 1200nm
Infrared Light Sources




Digital IR photography typically relies on a NIR light source       Maglite
          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
           Bandpass Filters
• Block wavelengths of light from hitting the
  digital sensor
• Allow wavelengths into the camera
• Filters have different characteristics
Predominately a Red Color Photographed
X-Nite Filters
X-NiteCC1                                     Bandpass: X-NiteBP1

            Filter Type   Center Wavelength   50% Transmission


            X-NiteCC1            483            325nm, 645nm


            X-NiteCC2          500nm            315nm, 730nm
IR Selective Filters

               BPB     BPG   BPR
Infrared Blocking / Visual Light Pass Filter
Ultraviolet Pass / Visual Light Blocking Filter
Other Glass Filter
  Equivalents:
Kaya PF4       780nm
Kaya PF2        830nm
Kaya PF1 & PF3a 1000nm
Hoya RM72      720nm
Hoya RM90      900nm
Hoya RM100     1000nm
M&K #078        780nm
M&K #093        830nm
M&K #095        850nm
 M&K 1000      1000nm
Wratten 18A     350nm
Wratten 29      620nm
Wratten 70      675nm
Wratten 89B     720nm
Wratten 88      735nm
Wratten 88A     750nm
Wratten 87      795nm
Wratten 87C     850nm
Wratten 87B     930nm
Wratten 87A    1000nm
Forensic IR Applications
Gunshot Residue
Black t-shirt

          GSR Particles




         T-shirt does not
         absorb Infrared light
IR Photography of GSR
Through Bloodstains


                             Blood Absorbs
                             In the IR




             GSR Particles
                  Oblique White Light




Fingerprints on
Lab Bench top




                                        Oblique White Light
                                           With IR Filter

								
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