In part two of his column on use of digital compact cameras, Mark Koekemoer explains how to get the most out of the built-in flash.
THE UNDERWATER WORLD IS FILLED with amazing creatures in a variety of colours. Trusted compact in hand, we head for popular hunting grounds with high hopes of obtaining the sort of images we see in magazines. But after surfacing and reviewing our images, we are disappointed to find that our photos are blue and dull. So why does this happen
The spectrum of light can be divided into the primary colours red, green and blue (RGB). Red wavelengths are short; blue are long.
As we descend on our dive, red is lost first, then orange, leaving greens and blues. It is the loss of red that leaves our photos looking so dull.
There are two ways of restoring colour under water: by taking advantage of the sunlight or by using artificial light. Im going to concentrate here on using the built-in flash as a technique for restoring colour. It is not depth-dependent, as photographing using natural light is.
The light from the built-in flash can be used to restore vivid colours under water, but you need to be aware of its limitations to have a chance of achieving this.
FLASH RANGE: Light, whether natural or artificial, is diffused and scattered as it travels through water. It bounces off suspended particles, significantly reducing the quality of the light returning through the lens.
The light from the built-in flash must reach the subject and then return through the lens for the sensor to capture it and record the image. This is known as the total light path.
The built-in flash on compacts is not very powerful. Designed for photographing in air,
under water its range averages 50cm to 1m in total.
WATER QUALITY: Having established the maximum working range of the flash, we need to consider the quality of the water between lens and subject.
Light travels in straight lines, from the flash to the subject and back through the lens. The built-in flash is usually situated close to the built-in lens, so if the water is turbid, the light from the flash will bounce off the particles and be reflected straight into the lens.
These reflections will be recorded on your image as bright specks, most likely ruining your photograph. This effect, known as backscatter, can be minimised by getting as close as you can, reducing the amount of water and suspended particles between camera and subject.
If you are plagued with backscatter and its hindering your potential to produce impressive images, the only way forward may be to invest in an off-camera flash, commonly called an external flash or strobe. This can be positioned in such
a way that only the subject is illuminated, rather than the particles in the water.
EXPOSURE CONTROL: On some cameras you can also control the exposure. Firstly, the aperture on your camera controls the amount of light entering the lens. It also controls the range at which the light will travel.
A wide aperture allows more light to travel to the sensor, and a small aperture reduces the light path.
If your camera allows, set the aperture to f2.8 for subjects that wont let you get closer than half a metre. Set the aperture to f8 for close-up subjects, to prevent over-exposure from the built-in flash.
Secondly, the shutter speed controls the ambient light. A slow shutter speed allows the sensor to be exposed for longer, letting in more ambient light. A fast shutter speed reduces the time that the sensor is exposed, letting in less light.
You may find that some of your pictures taken with the built-in flash are blurred. This is because the camera is choosing a slow shutter speed of perhaps a 30th of a second.
To prevent this blurred effect, set the shutter speed to no slower than 100th of a second.
Thirdly, control the flash output through the menu system. So if you find the flash to be too little or too much, simply increase or reduce the flash output.
DIFFUSERS: Your built-in flash photography will benefit from the use of a diffuser, which is usually in the form of a white opaque piece of plastic.
The diffuser is attached to the outside of the housing in front of the built-in flash. As the light from the flash travels in a straight line, the front port of the housing, which accommodates the cameras lens, may obstruct the light. The result is a harsh shadow cast over one side of your image.
Shadows are even more prominent when working very close to a subject. Using the diffuser can help to spread the light, evenly illuminating the scene.
If you have a supplementary wide-angle lens, its best to remove it, as it will also cast a shadow.
The image area of a wide-angle lens is also too big for the built-in flash to illuminate.
Using the built-in flash within its limitations can get you colourful images. Alternatively, for a different look altogether, we can switch off the built-in flash and experiment with natural light.
Next months PhotoCall covers natural lighting techniques using white balance and filters.
The theme for April entries is -
“Colourful Creatures - Images taken with a Compact & Built-In Flash”.
Marks clownfish wins £300 photo prize
Taking top place in the April heat of DIVER magazines PhotoCall competition is this clownfish taken by Mark Watts of Caloundra, Australia, with an Olympus C-765.
The theme was Colourful Creatures, and Mark wins a £300 INON UK voucher redeemable against lenses, flashguns or accessories.
He also goes forward to the judging next year for the grand prize a £2800 two-week trip to the annual Atlantis Foto Festival in the Philippines.