There are basically two ways to capture infrared images with a digital camera. The first uses an appropriate filter on the camera lens, and the second requires the camera to be converted to a given IR wavelength. Regardless of how you choose to do it, all colours rendered by an infrared image are termed false colours as they represent an interpretation of the different absorption and reflection of infrared light falling on the subjects in the photograph.
Prior to digital cameras, the only way to capture an IR image was to use a filter on the camera lens. Filters can also be used today on digital cameras. For example, an R72 filter blocks all light up to 720nm, allowing IR light to pass to the camera’s film or sensor.
Most digital camera manufacturers place a filter in front of the sensor that absorbs a significant amount of the IR light that passes through the lens, thus using an IR filter necessitates long exposure times, often on the order of tens of seconds. Some cameras are totally unsuitable for IR photography using filters, because the blocking filter in front of the sensor has become extremely efficient at removing IR light. If you are shooting with a filter, then you will need a tripod and a cable release as well.
The other approach is to convert a camera to only capture IR light. The main disadvantage to this is that the camera will only shoot images at the wavelength of the conversion. The main advantage is that images can be captured in the same way a regular DSLR does: hand-held, or on a tripod. The following describe the options for camera conversions.
590nm – Super (Ultra) Colour – This filter allows some of the visible light to pass through it and can give interesting foliage and sky colours. Swapping the red and blue channels in Photoshop gives the foliage a golden colour and the sky a very nice blue tone, as seen in the first image in this post. This IR filter can also provide good black and white images, particularly if you want full control of post processing and like to experiment with your conversion software, like that in the second image. This filter is a common choice of many photographers, including me.
665nm – Enhanced (Extra) Colour – This filter allows some of the visible colour to pass and will yield false colour IR photographs, although the colour and saturation range is not as great as that provided by the 590nm filter. Black and white images are similar to those of the 590nm filter, but may require a bit more experimentation to get the effect you are looking for.
720nm – Standard Infrared – It is considered a good, all around infrared filter choice. Colour infrared is possible, although the images are not as saturated as from the 665nm filter, and only the blue sky effect is possible, as seen in the third image on this post. Black and white IR images have good tonal range.
830nm – Deep Black and White – With this filter the image is captured in black and white straight out of the camera, as in the last image in this article. There is no need to manipulate in software unless you want to fine tune the black and white look. This is a strong filter producing the darkest sky and whitest foliage.
A more detailed treatment of these filters and illustrations for each can be found here.