Properly adjusted white balance settings let your camera see the colour in naturally lit underwater scenes..

Keeping it natural

hspace=5 Shooting with natural light and white-balance set is one answer to colour problems - at least in shallower waters, says Mark Koekemoer

Last month I looked at the problem with colour under water and how to restore it using the built-in flash. This approach did however have some limitations - and these can often be overcome by disabling the flash, and taking advantage of the sunlight.
The human eye and the camera see colour quite differently. Under water, light levels are usually lower than those in air.
Towards the end of a dive the visibility may appear to get better, but usually it is only your eyes adapting to the low light levels that creates this illusion. Its the same as when you switch the lights off at night before you go to bed. At first you cant see your hand in front of your face, but soon your eyes adjust, and objects slowly appear from out the blackness.
Even though we know that colours are lost as we go deeper, our brain will trick our eyes into seeing red in objects it knows should be red.
Our cameras, unfortunately, are not so clever. We have to programme them to see the right colours, and this is achieved by controlling the white-balance setting.
White balance is related to colour temperature. For example, mid-day sunlight will look much closer to white than early-morning or late-afternoon sunlight, which appears closer to yellow.
Similarly, a white wall will look different depending on the temperature of the light falling on it, and whether the source is the sun, incandescent light-bulbs or candles.
Most digital cameras have an automatic white-balance setting. They take a reading of the overall colour of the image, and calculate the best-fit white balance.
The automatic system often gets fooled, however, especially if the scene is dominated by one colour, for example blue. The most accurate way of achieving a natural colour balance is to use the cameras manual white-balance function, also known as custom white-balance.
Tipping the balance: The process involves pointing the camera at a white object, then pressing a dedicated button, indicated by your camera. At this point the camera locks into its memory what white looks like under the lighting conditions when you took the reading.
The rest of the colours are now balanced. Make sure that the flash is turned off - suppressed - or the colours will be unbalanced.
Experiment at home. Do a white-balance setting by pointing at a red, green or blue object. What you should see are blue, red and yellow hues respectively dominating your picture.
Now point your camera at a white object such as a sheet of paper or a wall, and set the white balance. All the colours you see should look normal through the camera.

Adjust for depth: Having learnt how to use your cameras white balance, lets take this under water.
As a reference, use a white slate. The reading is best taken with the sun behind you, so the light can bounce off the slate into the camera lens.
While descending, I usually take a white balance reading every 3 or 4m. I do this because, as the light levels drop the deeper I go, the harder it gets for the camera to take a reading.
If the light levels are too poor, the camera wont be able to take another reading, and will store the last one in its memory.
The same applies on your way up. Every time your depth changes by 3 or 4m, take another reading to keep the colour balance accurate.

Sunlight zone: Using custom white balance will make a big difference to your images by reproducing natural colours. For best results, shoot in the 5-15m range. There is usually enough sunlight between the surface and 5m.
Remember that the camera relies on sunlight, so the more light the better. This is why natural-light photography benefits greatly from the use of a wide-angle lens.
Because the field of view is much wider than that of the camera, it gathers far more sunlight.
Sunlight has to travel to the subject, and then through the lens. With a wide-angle lens you can get closer to your subjects, so the total path the sunlight has to travel is minimised, and colours are less diffused and appear more vibrant.

Using filters: While using white balance will improve the colour in your photos, some feel that combining this approach with colour- correction filters creates richer colours.
Filters are designed to absorb their opposing colours, so balancing the colour reproduction. Most common for underwater use are red filters, which absorb blue and green; and magenta, which absorb green.
Red filters are used in blue tropical waters and magenta in green temperate waters.
If your housing will allow it, you can screw a filter on the front, so that you can take it on and off during the dive. If not, you may have to use an internal device such as the Magic Filter, which commits you to natural light for that dive. Push-fit filters are also available.

 The theme for May entries is -
 “Water & Light - Images taken with a Compact with Natural Light only”.

Catherine snaps a £300 winner
Taking top place in the May heat of DIVER magazines PhotoCall competition is this grey nurse shark study by Catherine Marshall of Upper Stondon, Bedfordshire, taken in around 5m of water at Latitude Rock, NSW, Australia, with an Ixus 90IS with Inon wide-angle lens.
The theme was Water and Light - Images Taken with a Compact Camera with Natural Light Only, and Catherine wins a £300 INON UK voucher redeemable against lenses, flashguns or accessories.
Each month at Divernet.com we offer you a new theme with the chance to win the £300 prize and, ultimately, a 2-week trip to the Philippines worth £2800.