Filme under vann

What do you need for underwater filming, and what is important to consider regarding lighting and camera work? Find out in this article by Maida Hals.

Plenty of feature films, documentaries, commercials and music videos use underwater cinematography. Being under water gives the images a special look impossible to get on land. However it takes a lot of knowledge and equipment to achieve these images.

Equipment
Obviously you need a scuba-diving license, and scuba-diving equipment. It is recommended, but not necessary, to use a closed circuit rebreather, meaning that you inhale and exhale into a tight loop so that there will leave no air bubbles in the water to be in the way for your filming. In addition, you need a camera with underwater housing, and some lights.

An underwater housing is a waterproof case (house) for your camera. You can get underwater housings that are very simple or the more complex and fully manual ones.The most simple ones only have trigger controls to turn the power on and off, and start and stop the tape. The iris and the focus are then either on auto or preset. However, it is also possible to get fully featured camera housings including access to almost any control you'd like.

Water vs. air
Water is 800 times denser than air. This means that when light enters the water, it interacts with the water molecules and particles, resulting in loss of light, colour changes, diffusion, loss of contrast and other effects. If you take a photo underwater at one metre distance, it will be similar to a photo above water at 800 metres distance, both looking blueish and lacking contrast.

Light under water
The way light changes underwater creates the typical underwater atmosphere, which gives creative possibilities not found on land.

The shape of the water is decisive as to how the light passes through it. Coming from air into water, a denser medium, parts of the light will be reflected back, and parts of it will enter the water.  Depending on the shape of the water, the light will form crinkle patterns or become diffused randomly in all directions.The amount of light that is reflected depends on the height of the sun (affected by location, time of day and season) and the condition of the sea. A rough sea will absorb more light while a mirror-like sea will reflect more.

If you go deeper than a couple of metres under the surface, you will need to take your own light source with you to restore colours and increase contrast. Unfortunately, you cannot use ordinary dive torches for shooting video because they are not powerful enough, and nearly always have a hot spot in their beam. A purpose-built video light is the best option. The power of the lamp you need depends on what result you want, but as a general rule you actually need more powerful lights for clearer water because there is more ambient light for it to compete with.

Color under water
Water acts as a filter. If you put a white light above a tank of water that is 300 meters deep, the colors from the white light will be filtered out selectively one-by-one the deeper it gets. For example, most of the red is gone from the light already after 3 meters, same with some of the orange, but less of the yellow. At 8 meters, most of the orange is gone.

At 11 meters, most of the yellow is gone. So it continues through the spectrum until all that is left is violet light, which also eventually fades out. At the bottom of this 300 meter tank of water, there would be little or no light.

If a diver is bleeding at 20 meters, where there is no red light, the diver bleeds a greenish-black blood. Filming this with a light would reveal startling colors not seen without light.

Underwater cinematography is used in commercials, music videos, documentaries and features.

Links:
Scubadiving in Wikipedia
International Underwater filmfestival

Skrevet av Maida Hals