The HOYA R72 Infrared filter is specifically designed for infrared photography with digital cameras and infrared film.
Infrared light starts in the high-red area of the visible spectrum at around 750nm and goes up beyond 1000nm. This light is not visible to the naked eye. Looking through the R72 filter it looks almost opaque because the filter is only passing light from the very high red edge of the visible spectrum and infrared light. Infrared photography yields very interesting, sometimes stunning, and creative result as object in a scene reflect infrared light differently than normal light.
Due to the nature of infrared light, filter factor and exposure compensation vary widely from visible light and depends largely on lighting conditions.