When people think of photography, they generally think in terms of color or black and white. But there's a third option: digital infrared photography.
Different wavelengths of light look different, and some wavelengths are not visible to human eyes at all. Really short wavelengths include gamma rays, x-rays, and ultraviolet light. We can't see them, but we can use them for medical and other applications.
Infrared
There is a spectrum of wavelengths that humans can see. The shortest visible wavelengths are seen as violet or indigo, and the longest look red. Blue, green, yellow, and orange have wavelengths in between the wavelength of indigo light and the wavelength of red light. Wavelengths longer than red that humans can't see are called infrared.
Photographs taken in the infrared region of the light spectrum create effects that can't really be seen with color or traditional black and white photography.
Appearance
Digital infrared photography appears in black, white, and shades of gray, but the effect is ethereal, with skin tones looking smoother and more glowing, and whites appearing creamier.
Digital infrared photography is becoming a popular option in wedding photography because of the beautiful effects it creates.
The problem that must be overcome with most digital cameras is that they are designed to block out infrared light. They do let in some of it, though.
How to set it up
With a digital camera, an attachable filter that blocks out all but infrared light, and a tripod, most people can make their own digital infrared pictures. The key is that exposure times will be really long to allow enough light in through the filter to make an image.
That's why a tripod is a necessity. Clearly, with weddings, digital infrared photography is generally used for portraits made beforehand, not the quick shots that are made after the ceremony or at the reception.
If you're lucky enough to still have a functional compact digital camera that was made before 2001, it probably doesn't have an infrared blocking filter. This is good because you won't have to deal with the super long exposure times that you would with newer cameras.
You can attach the IR filter and shoot as if you were taking "normal" photographs. Of course, some experimentation will be necessary to determine how to get results you like.
Newer digital cameras have an infrared blocker called a "hot mirror" to make the sensor's visible light performance better. This means you'll have to do long exposures and will need a tripod.
There are services that will remove the hot mirror from compact digital cameras and replace it with clear glass. There are also tutorials on the Internet that will walk you through the process of removing the hot mirror yourself, but it's not a good idea to try this on your only camera unless you won't be too upset if you break it.
But before committing to something as drastic as "camera surgery," give infrared a chance using your tripod and filter. With enough experimenting with ISO and aperture settings, you may be able to get good infrared results while keeping the hot mirror intact.
If you do have a compact camera modified to remove the hot mirror, you simply add the infrared filter and shoot as if you were taking regular photographs. The camera should be able to focus on the fly and allow you to make infrared pictures quickly.
The filter you choose for digital infrared photography should allow in at least 90% of the IR light just beyond the red end of the spectrum, yet block almost all visible and UV light. The filter looks opaque and black, but it does let infrared rays through. We just can't see them because the human eye doesn't see in the infrared.
With non DSLR cameras, the infrared filter can often be made to fit using an adapter tube and ring. The filters will cost between $50 and $100, but they're often available used. For DSLRs, the filter should fit right onto your lens, so you won't need an adapter.
The main way to learn to use digital infrared photography to get images you like is the same way you learn to take any other kind of picture: experiment with camera settings (aperture, ISO, and white balance primarily), and take many, many pictures until you figure out how your particular camera should be set to get the results you want.
With practice, infrared photography can become a useful and creative addition to your repertoire of techniques.