IR photography opens up a new visual dimension for the photographer, a somewhat 'different' way of looking at the world around us. The spectrum of light is much wider than what the human eye can capture and, until CCD sensors became affordable to the general public, the only way to capture infrared radiation was to use special film, indeed sensitive to this part of the spectrum. Many are the applications of IR photography, from criminology to photomicrography and celestial photography. We shall focus here on landscape photography, but the reader interested in experimenting in other fields should be well aware that what is discussed here is the classical tip of the iceberg.
One of the fascinating features of IR photography is its ability to penetrate haze and light fog. As we have discussed above, infrared radiation has a longer wavelength than visible light and can 'go through haze’ more easily. This is becoming, unfortunately, more and more important as the level of pollution in the air increases. Some even go as far as theorizing that 'moderate' monochrome IR photography3 may become the de facto standard in landscape black and white photography, as finding truly crisp and clear days is getting more and more difficult.
Any radiation can be characterized by its wavelength, and light is of course no exception. What we consider as “light” is in fact visible light, i.e., that part of the radiation spectrum that the eye can indeed capture. We see various color hues, going from violet through blue, and then green, then yellow, then orange, and finally down to red and deep red. Below deep red there is radiation the human eye cannot see, i.e., infrared (IR). Although the human eye cannot see infrared radiation, the human body can certainly feel and react to it. Infrared is often perceived as heat.
In what follows we will focus on infrared photography, a technique that can capture on a digital sensor the IR radiation reflected by the scene we frame. IR radiation does start below a wavelength of 750nm and continues down to 20,000nm or more. However, digital sensors are seriously limited in their capability to record IR radiation. Digital sensors can go as far as 1300nm. Commercial IR films are unable to record radiations below about 900nm.
IR photography opens up a new visual dimension for the photographer, a somewhat 'different' way of looking at the world around us. The spectrum of light is much wider than what the human eye can capture and, until CCD sensors became affordable to the general public, the only way to capture infrared radiation was to use special film, indeed sensitive to this part of the spectrum.
It turns out that most digital cameras are quite capable of capturing infrared light. The trick with taking IR pictures is to put an IR filter on the camera. A readily available and moderately price IR filter is the Hoya R72. This filter is a high-pass filter, i.e., it blocks all wavelengths that are below a certain 'cut-off' wavelength. In the case of the Hoya R72 this wavelength is about 700nm (nanometers, a nanometer is one billionth of a meter). All the visible light, ultraviolet light, and so on will be blocked by the filter and will not go through it. Only the infrared light will be allowed to pass through the filter.
Below are several comparison shots of color versus infrared. For the comparison I used a Pentax K100D and the kit (18-55mm) lens. I took two shots from the same location, one in visable and the other in IR. For the IR shot I used Hoya R72 filter.