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Photographing The Invisible

Photographing The Invisible. Using Invisible Light. Keene State College. Rich Blatchly. Digital Sensors. Sensors are opaque, and are designed to detect only one color. Sensors are grouped (blue, red, and 2 greens). Each pixel yields a full spectrum, but two colors are interpolated.

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Photographing The Invisible

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  1. PhotographingTheInvisible • Using Invisible Light

  2. Keene State College • Rich Blatchly

  3. Digital Sensors • Sensors are opaque, and are designed to detect only one color. • Sensors are grouped (blue, red, and 2 greens). • Each pixel yields a full spectrum, but two colors are interpolated.

  4. Visible Light

  5. Digital Infrared Photography • Note that silicon (basis for photosensors) is sensitive to IR. http://www.luminous-landscape.com/reviews/cameras/infrared%20dslr.shtml

  6. What's different about IR

  7. More IR Differences

  8. Diagram of Apparatus • IR requires a source (sun?), a filter and an IR sensitive camera

  9. Camera equipment • Testing your camera

  10. Filter Responses • The common Wratten 89B is also called Hoya R72 http://wrotniak.net/photo/infrared/index.html#FILTER

  11. Aren’t Filters Expensive? • Find a bottle cap that fits over your P&S camera lens • A piece of unexposed, processed slide film can be a filter. http://www.instructables.com/id/EMW6NFO0FPEQHO9ZGG/

  12. Taking the picture • Exposure • In many cases, built in is OK • Try underexposing the photo to avoid red channel overload. • With 0.1% of light, exposure changes by 10 “stops”. (Each stop is x2 in exposure; 210 = 1024). • Focus

  13. Processing http://wrotniak.net/photo/infrared/c5060.html

  14. Mixed with Visible http://www.rbfotografia.com.br/Bruna/natureza/content/B6_large.html

  15. http://farm1.static.flickr.com/61/154130385_c0694b74f6_b.jpg

  16. How do leaves reflect IR? http://pirlwww.lpl.arizona.edu/research/biosphere/Lesson/

  17. Young and Mature Leaves

  18. Reflection depends on Health of Leaf • Chlorophyll absorbs red and blue light and reflects green light. • Near-infrared light is reflected by the spongy cell structure inside of leaves. • Chlorotic (yellow) leaves have lower levels of chlorophyll • Necrotic leaves do not have pigments or the spongy cell structure of living leaves.

  19. Other structural color • Leaves may appear lighter (gray, silver, white, blue, copper, or gold, due primarily to structures formed on the leaf surface that increase reflectance Turtleback, Psathyrotes ramosissima (Family Asteraceae),

  20. Desert Brittlebush • These leaves reflect about 60% of solar radiation, thus reducing leaf heating and stress. Encelia farinosa (Family Asteraceae)

  21. Forensic Uses of IR • Differences in ink can be detected in altered checks http://www.neiai.org/index.php?option=com_docman&task=doc_download&gid=28&Itemid=54

  22. Absorption Spectra of Inks http://www.fbi.gov/hq/lab/fsc/backissu/oct1999/mokrzyck.htm

  23. Forensic Uses of IR • Writing on charred paper can be imaged http://www.neiai.org/index.php?option=com_docman&task=doc_download&gid=28&Itemid=54

  24. Bloodstains • Just as inks can be transparent in IR, fabric dyes can reflect, revealing blood patterns. http://www.neiai.org/index.php?option=com_docman&task=doc_download&gid=28&Itemid=54

  25. More Bloodstains • Where is the real crime?

  26. Infrared Fluorescence • Infrared Fluorescence is similar to UV/Vis fluorescence, but shifted in frequency/wavelength. http://people.rit.edu/andpph/text-infrared-luminescence.html

  27. The Photophysics http://www.beyondvisible.com/BV0-Barebasics.html

  28. What does IR Luminescence Show?

  29. Wood in IR Fluorescence • Wood is typically dark in IR, but pigments can absorb visible light and emit in the IR.

  30. Camera Obscura • First reported in the 11th century by Al-Hazen of Egypt. • Arabic “quamera” or dark,gives us camera. • Used by artists and scientists • Some examples still survive (this is in San Francisco). http://en.wikipedia.org/wiki/Camera_obscura

  31. Lenses • Simple lenses have problems • Long working distances • Color errors • Weight • Reflections (internal and external) • Complex lenses with coatings used http://micro.magnet.fsu.edu/primer/java/lenses/simplethinlens/index.html http://micro.magnet.fsu.edu/primer/java/lenses/magnify/index.html http://micro.magnet.fsu.edu/primer/java/microscopy/variablelens/index.html

  32. Complex lenses • Modern lenses use multiple elements with coating, different refractive indices and the ability to move as groups or alone while focussing and zooming. • Phew! http://www.opticalres.com/kidoptx.html#Lenses

  33. Aperture and Shutter • These control exposure • Wider aperture increases light, decreases depth-of-field. • Slower shutter increases light, increases potential blur.

  34. Understanding f-stops • Longer focal-length lenses (telephoto) collect less light than shorter lenses (wide-angle). f-stops help us correct for this. • The aperture size is divided into the focal length to give the f-number • For a 50 mm lens, a 25 mm aperture is half the focal length, therefore f/2. • Apertures are arranged in factors of the square root of 2 (1.4, 2, 2.8, 4, 5.6, 8, etc.), yielding 1/2 the light for each stop.

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