Standard film cameras can be used for infrared photography provided the film advance and data back systems do not incorporate infrared sensors. Infrared film, which may still be available in colour or black-and-white, is sensitive to some of the longer wavelengths of electromagnetic radiation not visible to the human eye or panchromatic film. Digital cameras can be modified for serious infrared work. We can therefore produce images influenced by wavelengths that we cannot otherwise see. This opens up new and exciting opportunities for photographing people, but some basic rules must be observed. First let's consider the use of infrared film because the traditional film-based technique illustrates clearly the principles involved.
Black-and-white infrared film should be kept cool and must be loaded and unloaded in complete darkness. Removing the film cassette from the canister or camera in daylight will cause fogging. The most evocative results are achieved using opaque infrared filters that absorb unwanted visible light. A red filter (No 25) is a good alternative. Note that infrared rays do not focus in the same way as visible light. Focus in the normal manner, note the focused distance, and then turn the focusing ring manually until this distance aligns with the infrared focusing mark on the lens.
Set the exposure initially to whatever your normal exposure meter indicates, and bracket widely using small or medium apertures. When exposing Kodak HIE infrared film at ISO 200 in direct sunlight, using a red filter, try bracketing around 1/125 second at f/8. A person's skin is recorded as white if the subject is in direct light. Skin in shadow will be recorded as very dark. Hair and eyes record in broadly the same way as with panchromatic film, but only very dark shades of lipstick will be visible. Fresh green grass and foliage are recorded like frost or snow. Consequently it is possible to create unusual and even surreal images.
Ektachrome EIR colour infrared film (no longer available) had only limited application for pictorial work, but was fun to try. It incorporated infrared-sensitive dye and delivered rather unpredictable false-colour images when exposed using a yellow filter. Focusing adjustment was not necessary. The film had to be stored in a freezer and used fresh because its infrared characteristics degraded rapidly at room temperature. Like black-and-white infrared film, it had to be loaded and unloaded in total darkness to avoid fogging. It could be processed using E6 chemistry.
The modern digital approach is somewhat easier but must still be understood. The prerequisites are discussed in the article Infrared Photography using a Digital Camera. Infrared simulations are also possible in Photoshop, but the results rarely match the qualities of "true" infrared images and are unlikely to deceive an experienced eye.