Red filters & color filters

Red and colour-correction filters for accurate underwater imaging

Underwater filters are optical elements that correct colour loss caused by absorption and scattering. They restore red and warm tones for a neutral image without affecting metering.

Water removes red first, then orange and yellow with depth. Colour loss increases rapidly with depth, so red filters suit clear blue water, while magenta filters balance green water in temperate regions.

Technical considerations for selecting filters at varying depths

Filter choice depends on depth, sunlight, and water type. In shallow zones correction is minor; at 3–20 m (≈10–65 ft) colour filters provide the best results.

• Blue tropical water: red or orange filters work to about 20 m (≈65 ft).
• Tropical green water: magenta filters suit 3–15 m (≈10–50 ft).
• Cold or dark green water: filters are less effective; artificial light is required.

Filter types, mounting methods, and port placement choices

Options include threaded filters, rubber slip-on mounts, and cut-to-fit sheets placed inside a port. The internal method is rigid, because it cannot be removed underwater.

Threaded sizes cover common diameters, while slip-on designs fit varied ports. Sheet filters can be trimmed to unusual housings, but plan depth-specific swaps before the dive.

Fluorescence imaging using excitation and yellow barrier filters

Fluorescence reveals organisms that emit visible light when excited by a filtered source. Emission commonly appears as greens, blues, or reds against a dark background.

Use both an excitation filter and a yellow barrier filter: fit the excitation filter to a torch or strobe, then place the barrier filter on the mask and camera to block stray wavelengths.

Ambient filters for lights and action cameras, depth-specific use

Ambient filters adjust light output to better match surrounding water and reduce harsh contrast. See the reference on ambient filters for technique and examples.

For action cameras, modular clip-on systems allow quick swaps by depth and water type. A practical overview is in the FLIP filter system and macrosystem article.

• Red attenuates first; depth changes balance
• Match filter type to water colour
• Plan swaps before entering the water
• Fluorescence needs both filter types
• Ambient filters tune artificial light