Underwater Photography Lighting

Ambient only lighting
The easiest image to light is one that is lit by the sun. With an ambient exposure, you simply meter the most important part of the scene and take the picture. Shooting with ambient only light produces an acceptable image only when there is not much color to begin with. This is often the case with large subjects like wrecks and big animals like whales. These subjects are too large to light with a strobe and they look perfectly natural with ambient-only light.

Ambient-only lighting is also used to shoot silhouettes. Examples of silhouettes are shooting fish backlit by the sun or a dive boat and/or divers silhouetted against the surface of the water. In these instances, you set the proper exposure for the sun and let everything else go dark.

The big problem with ambient-only lighting is a noticeable lack of color, which is due to the absorption properties of the water column. It is frustrating to shot colourful fish and corals under these circumstances because the final image does not portray the true color of the subject. In very shallow water you will get some color, but as you go deeper, everything turns bluish. Remember, your eyes adjust to the loss of light and will compensates it, the camera does not. There are color-correcting filters designed to help restore some of the absorbed colors, but they are not as effective as using a strobe to restore the full spectrum.

Shooting with strobes
The majority of underwater photographs are lit with strobes because they can restore true colors within their range of about 5ft. There are two types of strobe-lit images: one where the strobe is the dominant light source and one where the strobe light is mixed with ambient light.

Strobe as dominant light source
The strobe is generally the dominant light source in macro and close-up photography. By definition these images are of solitary or small groups of fish or small invertebrates. These subjects often have backgrounds that reflect light, such as sand or a soft coral, and will be visible in the image.

When the background is the water column, it will record as black, unless you go out of your way to show it otherwise. In macro, you generally use very small apertures (f11, f16, f22) to maximize the depth of field. If you want to show the water background as blue or green, you have to use a wide aperture (f2.8, f4, f5.6) set for the ambient exposure. These apertures reduce the depth of field in a macro shot to almost nothing. That is why macro shots often have black background. It is more important to have greater depth of field than to show the color of the water.

Macro shots are the easiest to expose and to light. With TTL flash, or manual strobe with an LCD screen, you can fire away with great confidence. You can lighten or darken an image by using the exposure compensation or by changing the ISO. As long as your strobe is set to TTL, simply changing the aperture will not change the exposure, because the camera automatically adjusts the flash output to match your change in aperture.

Using two strobes
The TTL function of your camera can handle two strobes very well by turning them both off when enough light has entered the lens, just as it does for one strobe. The considerations are where to mount the second strobe and where to position it in relation to the other strobe.

The first strobe is mounted on the left side of the housing with a second strobe on the right side. The strobes can be connected by a dual cord with a Y-cable that connects to each strobe with the base of the Y connecting to the camera sync socket. If the housing has two sync sockets, you can use two single strobe cords so each strobe will connect to the camera independently.

The biggest challenge in using any second strobe is where to place it in relation to the main strobe. There are several considerations. Is your second strobe the same model as the main one? If not, is it more or less powerful? If your strobe have different power outputs, the more powerful one becomes the main strobe. In this case, the strobes can be at the same distance from the subject and will function as a main and a fill due to their different power outputs.

If your strobes are the same model, or the same power, you will need to vary the distance for each in relation to the subject. The idea is to light the subject with the main light and add some fill to reduce harsh shadows, the strobes are turned on and off by the camera at the same time, so if both strobes are at the same distance from the subject, they will light the subject equally. There would not be any shadows and your subject will appear flat. To get the main/fill effect, move the fill strobe a bit further away from the subject. That way, more light from the main strobe and less light from the fill strobe will reach the subject.

Combining strobe and ambient lighting
And lastly, the most challenging shots to light properly are those that balance strobe and ambient light. Here you use strobe light to restore colors and ambient light to record the background. This type of image is best characterized by the close-focus, wide-angle (CFWA) shot. I will cover this in the next article.