Using Strobes in Underwater Photography

In a previous article, we discussed how ambient light can be used in underwater photography. This time we will find out how submersible flash units or strobes are used to illuminate a subject or an entire scene.

Since water is much denser than air, light underwater is absorbed faster and at a shorter distance compared to light above the water surface. In cases when ambient light is simply not enough to adequately light up a scene, strobes come to the rescue by providing bright light even at deeper ocean levels. Another asset of using strobes is that they can show off the subject’s real colors. One of the properties of water is it lets the blue end of the spectrum pass through deeper than all the other color wavelengths, which makes underwater scenes acquire a blue cast. Strobe lights, with their complete light spectrum, can illuminate the subject or scene and present all the colors as they really are, without the predominant bluish color cast. Strobes can also act as fill light by lighting up the foreground or the dark areas of a subject while ambient light illuminates the rest of the scene.

Aside from presenting the subject’s color in full, there are other key differences between the results of strobe light and ambient light. Strobes can effectively freeze action since it can rapidly blast bright light. This allows for a fast shutter speed and there is no worry that camera or subject movement might cause the shot to come out blurry. Strobes will also provide strong light at short distances, and subjects taken at close up can be better illuminated. The added advantage to this is you can use a smaller aperture which means your camera covers a greater depth of field allowing more of the scene to be in focus. Strobes are not as useful in long distances, however, since the strobe light is absorbed by water. Distances of five feet or more no longer get illuminated and this is where ambient light can come in handy since it can encompass a larger area.

If you’re using only one strobe, try positioning it above and to the side of the camera, at a 45 degree angle to the subject. This lessens the appearance of visible particles (a.k.a. backscatter) in the water which can cloud up the image. Two strobes are ideal to lessen hard shadows that can appear if only one strobe were used. Using a pair of strobes on either side of the subject will provide more even lighting. Have one of the strobes provide lesser output to show a light shadow that will give the impression of depth. If the two strobes were giving off equal light output, the subject can come out looking flat and bland.

Keep in mind that strobe lights can be rather bulky and effort is required to set them up and maintained in proper position. Assistance from a dive buddy would be nice but if you don’t have one, you can use strobe arms with success. These arms are articulated for better positioning control of the direction of the strobe lights.