Photographing The Invisible

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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. - PowerPoint PPT Presentation

Transcript of Photographing The Invisible

  • PhotographingTheInvisibleUsing Invisible Light

  • Keene State CollegeRich Blatchly

  • Forming an ImagePatterned LightLensesApertureShutterFocal planeLight-tight box

  • Digital SensorsSensors 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.

  • Visible Light

  • Digital Infrared PhotographyNote that silicon (basis for photosensors) is sensitive to IR.

  • What's different about IR

  • More IR Differences

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

  • Camera equipmentTesting your camera

  • Filter ResponsesThe common Wratten 89B is also called Hoya R72

  • Arent Filters Expensive?Find a bottle cap that fits over your P&S camera lensA piece of unexposed, processed slide film can be a filter.

  • What to shoot in IRArial Photography in your backyard

  • Taking the pictureExposureIn many cases, built in is OKTry 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

  • Processing

  • Mixed with Visible


  • How do leaves reflect IR?

  • Young and Mature Leaves

  • Reflection depends on Health of LeafChlorophyll 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 chlorophyllNecrotic leaves do not have pigments or the spongy cell structure of living leaves.

  • Other structural colorLeaves may appear lighter (gray, silver, white, blue, copper, or gold, due primarily to structures formed on the leaf surface that increase reflectanceTurtleback, Psathyrotes ramosissima (Family Asteraceae),

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

  • Forensic Uses of IRDifferences in ink can be detected in altered checks

  • Absorption Spectra of Inks

  • Forensic Uses of IRWriting on charred paper can be imaged

  • BloodstainsJust as inks can be transparent in IR, fabric dyes can reflect, revealing blood patterns.

  • More BloodstainsWhere is the real crime?

  • frogs with infrared reflective pigmentSome frogs have an infrared reflective pigment to reduce heating

  • How to do infrared photography-SourcesWrotniakApogee 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

  • Infrared FluorescenceInfrared Fluorescence is similar to UV/Vis fluorescence, but shifted in frequency/wavelength.

  • The Photophysics

  • What does IR Luminescence Show?

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

  • Capturing the imageChemical processesNiepce (1827): Bitumen of JudeaDaguerre (1839): DaguerreotypeWilliam Fox Talbot (1839): CalotypeFrederick Archer (1851): CollodionRichard Maddox (1871): GeletinGeorge Eastman (1884): Celluloid support

  • UV Photography

  • Camera ObscuraFirst reported in the 11th century by Al-Hazen of Egypt.Arabic quamera or dark,gives us camera.Used by artists and scientistsSome examples still survive (this is in San Francisco).

  • LensesSimple lenses have problemsLong working distancesColor errorsWeightReflections (internal and external)Complex lenses with coatings used

  • Complex lensesModern lenses use multiple elements with coating, different refractive indices and the ability to move as groups or alone while focussing and zooming.Phew!

  • Autofocus--how does it work?

  • Aperture and ShutterThese control exposureWider aperture increases light, decreases depth-of-field.Slower shutter increases light, increases potential blur.

  • Understanding f-stopsLonger 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-numberFor 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.

    Visiting Professor Explores Light Perception in the Infrared - Daily Nexus Recommendation: I believe the most useful, general-purpose IR filter for digital photography is Hoya R72 (#89B). It blocks visible light well enough (if not entirely) to provide a well-pronounced IR effect, while still allowing for non-exotic exposure times. This filter should work fine with most of mid- to high-end amateur digital cameras (your mileage may vary, so check with someone who tried it on your camera). The small amount of visible (far red) light which this filter lets through does not affect pictures enough to spoil the IR effect, while coloring your images red (or purple), therefore they need to be converted to monochrome in postprocessing.Aerial Photography in Your Schoolyard [taken from APSnet ref above).Perspective can change how we view things. When we observe the world around us, changing our perspective can give us a more complete picture. Picture the playground at your school, or a nearby park. Perhaps there are areas of dead grass, or areas with lots of weeds. How could you measure how bad the problem is? Walking around the playground will give you an idea, but what if your playground is very large? That might require a lot of time. If we could go up in a helicopter or airplane, we could see the whole playground at once. If we took a camera with us, we could take a picture, and later measure the area showing the problem. Can you think of other ways of getting a camera above your schoolyard? Some people have tied cameras to balloons or kites.There are numerous web sites where people describe their experiences and how they set their cameras. Some of them are listed below.

    40 Incredible Near-Infrared Photos Smashing Magazine When setting the exposure compensation (SLR or not), you have to aim for a picture which will look like it is underexposed, too dark. This is because practically whole image information goes into just one of the RGB components: red, and you have to keep that component from saturation (i.e., running out of range). If your camera can display a brightness histogram for individual RGB components, make sure that the red one does not hit the upper limit. Otherwise use -1 EV or so of negative exposure compensation, adjusting this correction as you learn your camera/filter combination.Your exposures will be quite long: an IR filter combined with the camera's anti-IR one will let through less than 0.1% of the incoming light. A bright scene, requiring 1/500 s at F/8 in visible light will need about 1 s or longer at F/4 on most cameras. Not only this asks for using a tripod, but, if the air is not quite still, there will be a blur in the foliage, grass, water reflections, etc. This is not necessarily a bad thing, and it may add an extra feel to the imag

    The lake at the front of my house is a nice IR subject, so here it is, on a late, August afternoon. The original image shot with the Hoya R72 filter is shown above at left; above right is the same file after desaturation, and at the right after some histogram adjustment.The R72 exposure adjustment factor for the '5060, i.e., the exposure difference between this picture and the one below, is 2400, or 11.2 EV (the same as for the '5050).Note that the exposure program in this camers boosts up the CCD gain quite aggresively: ISO 250 in this case. This does not help the noise, usually prominent in infrared, but I don't mind it reallyThe figure below shows how red (R), green (G), blue (B), and infrared (IR) light is reflected by a leaf. The palisade tissue containing chloroplasts absorbs