Clarifications: The frequency of infrared light is lower than visible light, rather than higher. Also, the sky looks black in infrared photos because it does not scatter the rays, rather than absorbing it.
In infrared light, water and sky look black and smooth like a chalkboard, plant leaves glow like bioluminescent jellyfish, and the red and white colors of a stop sign blend together to make a dull grey-colored octagon. Caltech physics professor Tom Prince, who was a sabbatical visitor to UCSB’s Kavli Institute for Theoretical Physics last quarter, captured these inverse negative-like images with his own slightly modified Fuji digital camera.
Infrared light has a range of wavelengths longer than the wavelengths of visible light, and it is thus invisible to the naked human eye. In the electromagnetic spectrum – where electromagnetic radiation waves such as light, x-rays and TV and radio transmissions are distributed by frequency and wavelength – infrared lights have a range between the microwave region and visible light. Those near the microwave region are known as far infrared lights, and they are produce heat, while those near visible light are not hot at all, and are used by TV remote controls.
The frequency of infrared light is lower than visible light, and its wavelengths are absorbed and reflected differently by objects compared to visible light. Prince said this causes a “spotlight effect” from the sun, which shifts contrasts and makes the landscape look surreal.
“Its like shooting in space,” Prince said. “When the sky is dark, shadows become deep, since there is no blue sky to illuminate them.”
Prince said plants look blindingly white in infrared due to their ability to reflect excess light. While some light is necessary for plants to perform photosynthesis, he said excess light can dry out or damage plant cells, and therefore vegetation’s ability to reflect exorbitant light is critical to its survival.
In contrast, Prince said man-made objects are darker and less eye-catching in infrared imagery because they do not reflect much light, and the sky looks black because it absorbs infrared rays. Additionally, he said water absorbs infrared light completely at certain depths, but reflects light on its surface, which causes water in infrared photos to look similar to crude oil.
As for the stop sign, Prince said in infrared, the camera sees white and red as the same color because white objects reflect all light, and cameras in infrared do not differentiate between the color red and infrared light.
The How-To’s of Infrared Cameras
Any digital camera can be converted into an infrared camera, Prince said, because all digital cameras have an electronic sensor that can detect infrared light.
“When you buy a [digital] camera, there is a filter which removes the infrared [light], so only the visible light is visible,” Prince said. “You have to get into the camera and remove the filter, which is usually right along the sensor.”
According to Prince, the filter is located under the camera lens, and once it is removed, images look softer.
“The camera picks up the part of the spectrum your eyes cannot see,” Prince said. “What you can say is that though our eyes cannot see [the infrared light,] the camera takes that wavelength and converts it into a form we can see.”
After removing the filter from his Fuji camera, Prince said he had to add a second filter that would block out most visible light and only allow infrared light to affect the sensor.
Initially, Prince said his camera’s photoreceptors, which are electronic sensors affected by light intake, caused his photos to have a heavy purple tint. In a camera, each pixel within a sensor contains four photoreceptors with either red, blue, or green filters. The blue and green receptors are blocked by the visible light filter, Prince said, but the camera does not differentiate between red and infrared light. Since the camera’s photoreceptors only sense how much light affects them, Prince said photos are made from interpreting light intensity, and the camera translates the intensity of red and infrared light as a purple tint. For this reason, he said he decided to take photos in black and white to correctly depict light intensity and to make the photos more aesthetically pleasing.
A Light Hobby
Prince said he began taking infrared photos after he experimented in extending light perception, and continued to take photos when he noticed they had an intrinsic appeal.
“I got into it not for pictures but to see how the world looks like in infrared,” he said. “[I took pictures of] cars, stop signs, buildings, just to see what they would look like.”
He said he started to post his photos on the Kavli Institute blog, “Far From Equilibrium,” in February, at http://kitp08.blogspot.com.