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Appeared in DIVER October 2010
New on the market - the Canon Powershot S-95.
Taming the compact
Whether you're buying your first or looking to upgrade, it's vital to understand the features that matter under water, says Mark Koekemoer
The lens is composed of optical elements that are concave and convex, and transmits light onto the sensor. The distance from the optical centre of the lens to the sensor is called the focal length. This is often expressed as an equivalent to 35mm film.
Lens specifications may refer to 35mm, 28mm or 25mm. The smaller the number, the wider the viewing angle of the lens. 28mm cameras are the most common, and offer you more flexibility when adding supplementary lenses to your housing.
Optical zoom is the ability of the lens to alter focal length. As it increases, so the image is magnified.
Compacts may have optical zooms of 3x, 5x, 10x or 12x. But while having a long zoom range may be beneficial on land, it serves little purpose under water, where you need to get close to your subject.
Zooming in may give you the illusion of getting closer, but you're still photographing through the same volume of water.
Digital zoom is the camera's ability to crop a scene and enhance the image. It cannot capture the same detail that the lens can, so the quality of the image is poor. Make sure that digital zoom is disabled under water.
The sensor is the component onto which the light falls. It consists of a mosaic of square tiles, often referred to as pixels. A camera with 8 million pixels is said to have 8 megapixels (8MP). The size of the sensor inside compacts is substantially smaller han that found in an SLR, which explains the
noise levels at higher ISOs on compacts...
The ISO rating on the camera indicates the sensor's level of sensitivity to light. The idea is that in low light conditions you can increase the ISO so that the sensor can capture more light.
The disadvantage of increasing the ISO is the introduction of noise. Red blemishes appear in areas of uniform colour or black in your image, spoiling them.
The low light performance of the camera will depend on the size and quality of the sensor. As a guide, use an ISO of about 100, and increase it only as a last resort.
AUTO EXPOSURE (AE)
All cameras have AE mode, whereby the camera selects the appropriate settings to expose the image correctly . AE works pretty well for topside photography, but it can have limitations for your underwater work, such as in colour correction, depth of field or control of the ambient/ background light.
Scene mode offers a variety of pre-set modes designed to suit various occasions. For example, "fireworks" will have the flash disabled and a slow shutter speed to capture streaks in the night sky.
This is where the Underwater mode can be found. It's a point-and-shoot setting that helps to capture colours using natural light. How effective this mode is depends on the camera brand.
P mode usually allows you to change the settings of certain functions, for example ISO and white balance. The ISO can be raised to take images in low light conditions, such as atmospheric shots inside wrecks, and white balance will allow more control over colour correction.
Some camera manufacturers label their Programme mode as Manual (M). This often misleads people into believing that the camera has Manual Exposure mode, when in fact it may not. This is explained in more detail below.
Most digital cameras will have an automatic white-balance setting, whereby the camera takes
a reading of the overall colour of the image and calculates the best-fit white balance.
But the automatic system often gets fooled, especially if the scene is dominated by one colour, like blue.
The most accurate way of achieving a natural colour balance is to use the camera's "manual" white-balance function, also known as "custom" white balance. Aiming the camera at a white or grey slate, take a white-balance reading.
APERTURE PRIORITY (A, AV)
The camera aperture is like the iris of our eyes, controlling the amount of light we see, or, in
the case of the camera, the sensor. In Aperture Priority, you select your desired aperture and the camera selects the shutter speed.
This is a particularly useful when using a flash. The aperture has a direct influence on the working range of your flash, so by being
able to control the aperture you can always make sure of getting the most out of it.
The aperture also allows you to control the depth of field in your image. If you want to blur the background, for example, select a large aperture of f2.8. For the opposite effect, use f8.
Shutter Speed Priority (S, TV)
Shutter speed controls the amount of time the sensor is exposed to light. The slower the speed, the longer the sensor is exposed, and vice versa.
You can control the ambient light with the shutter speed. Fast shutter speeds against open water will yield a black background, while slow speeds result in deep to light blue backgrounds.
Slow shutter speeds can also be used to create motion, a creative effect called motion blur.
If your camera does not support aperture/ shutter priority, your best bet is to use the exposure compensator. This lets you under-or over-expose the image, within a two-stop range either way, (-2 / +2). Try under-exposing to get deep blue backgrounds, or to tone down the flash if you find it overexposing.
Start taking control of your photography by using Manual Exposure mode, and choose the aperture as well as the shutter speed.
You can now experiment with balanced-light photography, where you balance the ambient light with that of the flash, creating a colourful, yet natural aesthetic to your images.
Next month - (November issue): How to maximise your chances of winning a competition!
WIN AN ATLANTIS FORTNIGHT
Our online PhotoCall competition gives you the chance to upload your best work to Divernet.com, and to win not only wider exposure and monthly prizes but, ultimately, a wonderful fortnight in the Philippines.
Each month at Divernet.com we offer you a theme, and invite you to upload up to three images. Mark Koekemoer selects the winning image, reproduced both online and in DIVER.
Jaws of victory
Placed top in October's Photocall Competition to suit the theme "Dangerous Creatures" was Alan Smith's portrait of a fang-tooth moray eel. Alan, of Retford in Nottinghamshire, wins a £300 INON UK voucher redeemable against lenses, flashguns or accessories.
A year on, the work of all 12 winners will be judged to find the winner of the Grand Prize - a £2800 two-centre, two-week trip to the Philippines, including all flights, full-board accommodation and unlimited diving!
This amazing prize is offered by Atlantis Dive Resorts, which has centres in two prime Philippines diving locations, Puerto Galera and Dumaguete, and runs the Atlantis Foto Festival (www.atlantishotel.com).
The winner will join Mark Koekemoer on an INON UK group trip to the festival in summer 2011, and Diver will reproduce the results of his or her diving experiences.
The theme for October entries is -
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