Underwater and marine cinematography

Water transforms light. It absorbs colours unevenly, scatters light from particles, bends rays at every glass surface and pressure-tests every seal on a camera housing. It also brings serious risks to people: drowning, cold, decompression illness and entanglement. Underwater cinematography, from a shallow pool scene to a deep ocean sequence, is therefore one of the most specialized fields in the industry. Marine work on the surface, from boats and docks, has its own challenges with motion, spray and safety. This lesson explains how water changes light and optics, how housings and ports work, how underwater lighting is planned, how dive operations are organized and regulated, and how the DP supervises underwater work without being a diver.

How water changes light

Water absorbs light, and it absorbs long wavelengths (reds) much more strongly than short ones (blues and greens). Sunlight that reaches a subject underwater has travelled down from the surface and then across to the camera, so the total path length matters, not just the depth.

Here I is the remaining intensity, I₀ the starting intensity, k the absorption coefficient for that wavelength and x the path length through water. In clear water k for red light is roughly 0.3 to 0.4 per metre, while for blue-green light it is much smaller. Suspended particles add scattering and further loss, and in coastal and lake water absorption and scattering are often far higher.

Practical consequences follow directly. Work as close to the subject as possible with wide lenses to minimize the water between lens and subject. Use artificial light for close subjects and white balance carefully, or use filters for ambient-light shooting in shallow water. Expect visibility, not just colour, to limit what can be filmed.

Housings and ports

Underwater cameras sit in waterproof housings, usually made of aluminium alloy or engineered plastics, sealed with O-rings and fitted with controls that pass through the housing to the camera. The lens looks out through a port, either flat or dome-shaped, and the port changes the optics.

• Flat ports: a flat window in front of the lens. Light passing from water to air bends at the flat surface, which makes subjects appear about 1.33 times closer and larger and narrows the field of view. Flat ports suit macro and longer lenses but cause distortion and colour fringing at wide angles.
• Dome ports: a curved window centred on the lens's entrance pupil. A dome largely preserves the lens's field of view in water, but it creates a virtual image of the scene a short distance in front of the dome, so the lens must focus close, often with a dioptre.
• Pressure ratings: each housing has a depth rating; never exceed it, and allow a margin.
• Seals and maintenance: O-rings are cleaned, inspected and lightly greased before each dive, and the housing is tested for leaks in shallow water or with a vacuum check before the camera goes deep.

Lighting underwater

Underwater lighting fights absorption and scattering.

• Place lights to the side of the camera, not next to the lens, so particles in the water are not lit directly toward the camera; this reduces backscatter, the "snow" effect of lit particles.
• Use wide, soft sources close to the subject for faces and close work.
• Plan power: underwater lights are often battery-powered or fed by umbilicals from the surface, with strict electrical safety rules such as ground-fault protection.
• In studio tanks, light from above through the surface, add underwater units and control reflections from tank walls.
• White balance on a grey card at the working distance, and keep notes as the depth or distance changes.

Organizing an underwater shoot

An underwater sequence is planned as a dive operation as well as a camera operation.

• Dive plan: depths, durations, breathing gas, decompression limits, entry and exit points and emergency procedures, approved by the dive supervisor.
• Team: underwater DP or camera operator, camera assistant and diving support, safety divers for cast and crew, a dive supervisor and surface support.
• Performers: actors must be assessed for water confidence and, where needed, trained; safety divers stay close with breathing gas for breath-hold performers.
• Communication: hand signals agreed in advance, underwater speakers for directions, and surface communication systems.
• Locations: studio tanks give control of light, temperature, visibility and safety; open water gives realism but adds weather, current, cold and visibility risks.
• Time limits: depth and dive time are limited by decompression rules, breathing-gas supply and cold, not by the shooting schedule.

Rules for occupational diving in Canada

In Canada, diving at work is regulated by provincial and federal occupational health and safety laws, which require dive teams with defined roles, qualified divers, dive plans and emergency procedures. CSA Z275.2, the occupational safety code for diving operations, and CSA Z275.4, the competency standard for diving, hyperbaric chamber and remotely operated vehicle operations, are referenced by many jurisdictions. For example, Ontario regulates diving under its Diving Operations regulation and British Columbia under Part 24 of its occupational health and safety regulation. Film and television productions are workplaces, so these rules apply to crew and performers who dive. Boats used in marine filming must meet Transport Canada's small vessel and safety equipment requirements.

Surface and marine work

Not all water work is underwater. Shooting from boats, docks and in surf brings its own techniques.

• Splash bags and splash housings: protect cameras close to the waterline and allow half-in, half-out shots with a dome port.
• Stabilization: boats roll and pitch; gyro-stabilized heads, gimbals and wide lenses help, and long lenses are hard to hold steady.
• Spray and salt: rain covers, spinning rain deflectors, fresh-water rinses and careful cleaning after every day.
• Marine safety: personal flotation devices, a vessel master in charge of the boat, man-overboard procedures and weather limits.
• Cold water: even in summer, cold water is dangerous; immersion can cause cold shock and loss of muscle control within minutes.

The DP's role when not diving

Many DPs do not dive. They still lead the look.

• Agree the look, lenses, ports, lighting style, frame rate and colour pipeline with the underwater DP in prep.
• Watch live video from underwater on monitors at the surface, communicating through the dive supervisor or underwater speakers.
• Match underwater footage to surface scenes in light direction, time of day and colour intent.
• Review dailies with the underwater team and the colourist.
• Respect the dive plan: time, depth and safety decisions belong to the dive supervisor.