When film was king, infrared photography was a specialized and tricky endeavor. Photographers who wanted to experiment with it were faced with challenges like keeping the film cool at all times and learning how to focus properly to get a sharp image. IR leaks in cameras were discovered by a trial-and-error process that frequently resulted in frustration, as whole rolls of film would be lost before one realized that there was a leak at all. When it came time to process, only a few labs had the expertise and facilities to handle IR film, and as if a roll wasn’t expensive enough, the processing costs were often at least two or three times the usual cost for a custom-processed roll of black-and-white.
By comparison, shooting digital infrared is easier and cheaper in every way. Once you have a camera converted, the shooting costs are practically negligible. You can see your results immediately on the LCD monitor and make adjustments before you miss the shot. The tedious practices of safely handling film are gone completely and, thanks to the D-SLR construction, IR leaks are practically unheard of.
Infrared camera conversion is done by removing the sandwiched anti-aliasing filter and infrared cutoff filter from the D-SLR and placing a new infrared high-frequency glass optic in its place. The infrared cutoff filter prevents infrared light from reaching the image sensor, so removal of this filter is the primary change within the body to allow the capturing of an infrared photograph.
Several companies convert cameras for dedicated IR use. The process differs slightly, depending on the company and what kind of IR conversion you want. The anti-aliasing filter combined with the infrared cutoff filter is what keeps your camera from absorbing the infrared spectrum—as a way of blocking or blurring it out.
One such company, LDP, has three options for infrared conversions. High Resolution keeps the infrared cutoff filter, but replaces the anti-aliasing filter. This specific conversion lets you take maximum resolution and color-separation photos without any filters. In IR-only conversions, autofocus and auto exposure work with any lens, giving you an IR-only picture. IR+Visible allows the image sensor to see infrared, ultraviolet and the visible spectrums of light.