USING STROBES UNDERWATER

by Gordon Sammut

Colour Loss

If you are a certified diver then you already know that water absorbs colour. All red disappears in as little as 1 metre of water. There are various ways to overcome colour loss underwater, most notably adjusting white balance, using filters, and using flash.
Adjusting the white balance is a way of instructing the camera to 'adjust' the colour frequencies it perceives and put the colours in their proper place. This can be of two kinds: (a) using an underwater scene mode, or (b) taking a manual white balance reading. Whilst both are a significant improvement over leaving the camera to cope with colour loss on its own (especially the latter), adjusting the white balance will not bring the colours back if they have been lost. Filters may also be useful in restoring some colour. Filters work pretty much like wearing sunglasses, they provide an overall shade to the picture. Yet at depth they block light and the colour correction they provide is indiscriminate, everything in the picture will be corrected even if it should not really be.

The only way to bring back colours underwater if they have been lost is to use an artificial light source, that is to use flash. Once you use a flash you will be able to see colours underwater as they truly are, and not as they appear. It is for this same reason that some divers carry a pocket torch in their BCD pockets and use it even in tropical waters with plenty of ambient light and great visibility. Using an artificial light reveals the splendor of the underwater world as it truly is.

Which flash?

Most underwater cameras come with a built-in flash and a diffuser to allow you to use flash underwater. For very close-up and macro shots in extemely good visibility, the built-in flash of the camera may be useful, but not much more than that. The camera's built-in flash is suitable on land, but underwater the light it delivers will likely be absorbed by water by the time it reaches the subject alone, nevermind coming all the way back to the lens. Generally, a more powerful light source is required. Moreover, as light is coming from a source very close to the lens, it will illuminate all the particles in the water between the lens and the subject resulting in white spots all over the picture. This is called 'backscatter'. Backscatter can be avoided by positioning the flash at an angle to the lens. In this way backscatter is created in front of the flash but not in front of the lens. For this reason underwater strobes are mounted on a tray on the side of the camera on a flexible arm. Using an underwater strobe in this way will restore colour to your underwater subjects and reveal them for what they truly are. There are a range of strobes in the market, and your choice must depend on the size of your lens, whether you intend to use a wide-angle lens with your camera, and what kind of composition you are after, that is whether a circular light beam is required for the shots you want to be taking. Give us a call if you need help in making your choice.

How does it work?

All of our strobes are available as stand alone or, more conveniently, in packages which contain all the requisite components (see Products, flash section). You need a tray onto which the camera is secured via the tripod screw on the bottom of the housing, and a flexible arm mounted on the tray on the side of the camera onto which the strobe is screwed. A fibre-optic cable connects the strobe to a velcro patch which is attached on the housing directly in front of the built-in flash. When the built-in flash fires, the patch will block any light from leaving the housing but the fibre-optic cable picks it up, relays to the strobe and fires it. The strobe 'slaves' to the built-in flash, and the fibre-optic cable ensures it slaves only to the camera's flash and not any other light (such as another diver's camera). The strobe's power is adjusted manually through a dial at the back.