Photographing The Invisible Using Invisible Light

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Photographing The Invisible Using Invisible Light Slide 2 Keene State College Rich Blatchly Slide 3 Forming an Image Patterned Light Lenses Aperture Shutter Focal plane Light-tight box Slide 4 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. Slide 5 Visible Light Slide 6 Digital Infrared Photography Note that silicon (basis for photosensors) is sensitive to IR. Slide 7 What's different about IR Slide 8 More IR Differences Slide 9 Diagram of Apparatus IR requires a source (sun?), a filter and an IR sensitive camera Slide 10 Testing your camera Camera equipment Slide 11 Filter Responses The common Wratten 89B is also called Hoya R72 Slide 12 Arent 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. Slide 13 Arial Photography in your backyard What to shoot in IR Slide 14 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; 2 10 = 1024). Focus Taking the picture Slide 15 Processing Slide 16 Mixed with Visible Slide 17 Slide 18 How do leaves reflect IR? Slide 19 Young and Mature Leaves Slide 20 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. Slide 21 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), Slide 22 Desert Brittlebush These leaves reflect about 60% of solar radiation, thus reducing leaf heating and stress. Encelia farinosa (Family Asteraceae) Slide 23 Forensic Uses of IR Differences in ink can be detected in altered checks Slide 24 Absorption Spectra of Inks Slide 25 Forensic Uses of IR Writing on charred paper can be imaged Slide 26 Bloodstains Just as inks can be transparent in IR, fabric dyes can reflect, revealing blood patterns. Slide 27 More Bloodstains Where is the real crime? Slide 28 frogs with infrared reflective pigment Some frogs have an infrared reflective pigment to reduce heating Slide 29 Wrotniak Apogee Photo Magazine: DIGITAL INFRARED PHOTOGRAPHY MADE EASY Point and Shoot Digital Infrared Photography: Get Creative with Invisible Light | A Guide to Infrared Photography | teddy- risation GentleIntro1 How to do infrared photography- Sources Slide 30 Infrared Fluorescence Infrared Fluorescence is similar to UV/Vis fluorescence, but shifted in frequency/wa velength. Slide 31 The Photophysics Slide 32 What does IR Luminescence Show? Slide 33 Wood in IR Fluorescence Wood is typically dark in IR, but pigments can absorb visible light and emit in the IR. Slide 34 Slide 35 Capturing the image Chemical processes Niepce (1827): Bitumen of Judea Daguerre (1839): Daguerreotype William Fox Talbot (1839): Calotype Frederick Archer (1851): Collodion Richard Maddox (1871): Geletin George Eastman (1884): Celluloid support Slide 36 UV Photography Slide 37 Camera Obscura ra_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). Slide 38 Lenses Simple lenses have problems Long working distances Color errors Weight Reflections (internal and external) Complex lenses with coatings used s/index.html x.html ens/index.html/ ens/index.h Slide 39 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! optx.html#Lenses Slide 40 Autofocus--how does it work? Slide 41 Aperture and Shutter These control exposure Wider aperture increases light, decreases depth-of-field. Slower shutter increases light, increases potential blur. Slide 42 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.