This CY filter is designed underwater color-correcting filter created specifically to correct colors in Caribbean or tropical blue-green (cyan) water. With sunlight and the URPRO filter, corals, fish and underwater life are accurately recorded in natural breathtaking beauty. The filter neutralizes the "underwater blues" so that the true colors with already exist are easily recorded on all films and video. (Reds, oranges and yellows usually exist at depths past 50-100 feet!) The filter used in blue-green (cyan) ocean water and direct sunlight will yield the best results. Conditions at the same location vary, often significantly. The results produced by the URPRO filter will depend upon specific water and light conditions. The CY Color Correction Filter can be mounted outside housing directly in between the port and the attached wet lenses.