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.
Digital Infrared Photography Note that silicon (basis for photosensors) is sensitive to IR.
What's different about IR
More IR Differences
Diagram of Apparatus IR requires a source (sun?), a filter and an IR sensitive camera
Testing your camera Camera equipment
Filter Responses The common Wratten 89B is also called Hoya R72
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.
Arial Photography in your backyard What to shoot in IR
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
Mixed with Visible
How do leaves reflect IR?
Young and Mature Leaves
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.
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),
Desert Brittlebush These leaves reflect about 60% of solar radiation, thus reducing leaf heating and stress. Encelia farinosa (Family Asteraceae)
Forensic Uses of IR Differences in ink can be detected in altered checks
Absorption Spectra of Inks
Forensic Uses of IR Writing on charred paper can be imaged
Bloodstains Just as inks can be transparent in IR, fabric dyes can reflect, revealing blood patterns.
More Bloodstains Where is the real crime?
frogs with infrared reflective pigment Some frogs have an infrared reflective pigment to reduce heating
Wrotniak Apogee Photo Magazine: DIGITAL INFRARED PHOTOGRAPHY MADE EASY Point and Shoot Digital Infrared Photography: Get Creative with Invisible Light | Suite101.com A Guide to Infrared Photography | teddy- risation GentleIntro1 How to do infrared photography- Sources
Infrared Fluorescence Infrared Fluorescence is similar to UV/Vis fluorescence, but shifted in frequency/wa velength.
What does IR Luminescence Show?
Wood in IR Fluorescence Wood is typically dark in IR, but pigments can absorb visible light and emit in the IR.
Capturing the image Chemical processes Nie´pce (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
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).
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/micro.magnet.fsu.edu/primer/java/microscopy/variablel ens/index.h
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
Autofocus--how does it work?
Aperture and Shutter These control exposure Wider aperture increases light, decreases depth-of-field. Slower shutter increases light, increases potential blur.
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.