Photographing The Invisible Using Invisible Light

Photographing The Invisible

  • Upload

  • View

  • Download

Embed Size (px)


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

Citation preview

Page 1: Photographing The Invisible




InvisibleUsing Invisible LightUsing Invisible Light

Page 2: Photographing The Invisible

Keene State


• Rich Blatchly

Page 3: Photographing The Invisible

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.

Page 4: Photographing The Invisible

Visible Light

Page 5: Photographing The Invisible

Digital Infrared Photography

• Note that silicon (basis for photosensors) is sensitive to IR.


Page 6: Photographing The Invisible

What's different about IR

Page 7: Photographing The Invisible

More IR Differences

Page 8: Photographing The Invisible

Diagram of Apparatus

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

Page 9: Photographing The Invisible

• Testing your camera

Camera equipment

Page 10: Photographing The Invisible

Filter Responses

• The common Wratten 89B is also called Hoya R72


Page 11: Photographing The Invisible

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.


Page 12: Photographing The Invisible

• 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

Taking the picture

Page 13: Photographing The Invisible



Page 14: Photographing The Invisible

Mixed with Visible


Page 15: Photographing The Invisible


Page 16: Photographing The Invisible

How do leaves reflect IR?


Page 17: Photographing The Invisible

Young and Mature Leaves

Page 18: Photographing The Invisible

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.

Page 19: Photographing The Invisible

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),

Page 20: Photographing The Invisible

Desert Brittlebush

• These leaves reflect about 60% of solar radiation, thus reducing leaf heating and stress.

Encelia farinosa (Family Asteraceae)

Page 21: Photographing The Invisible

Forensic Uses of IR

• Differences in ink can be detected in altered checks


Page 22: Photographing The Invisible

Absorption Spectra of Inks


Page 23: Photographing The Invisible

Forensic Uses of IR

• Writing on charred paper can be imaged


Page 24: Photographing The Invisible

Bloodstains• Just as inks can be transparent in IR,

fabric dyes can reflect, revealing blood patterns.


Page 25: Photographing The Invisible

More Bloodstains

• Where is the real crime?

Page 26: Photographing The Invisible

Infrared Fluorescence

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


Page 27: Photographing The Invisible

The Photophysics


Page 28: Photographing The Invisible

What does IR Luminescence Show?

Page 29: Photographing The Invisible

Wood in IR Fluorescence

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

Page 30: Photographing The Invisible
Page 31: Photographing The Invisible

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).

Page 32: Photographing The Invisible


• Simple lenses have problems

• Long working distances

• Color errors

• Weight

• Reflections (internal and external)

• Complex lenses with coatings usedhttp://micro.magnet.fsu.edu/primer/java/lenses/simplethinlens/index.html



Page 33: Photographing The Invisible

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!


Page 34: Photographing The Invisible

Aperture and Shutter

• These control exposure

• Wider aperture increases light, decreases depth-of-field.

• Slower shutter increases light, increases potential blur.

Page 35: Photographing The Invisible

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.