Loss of Light and Loss of Colour " Scuba diving "

If you are 7 m deep and 3 m from your subject, the total light path is actually equal to 10 m. For another example, cast your mind back to an occasion of good visibility in 10 m of water. Can you remember that your eye saw a much more colourful spectacle than your camera was able to record? This was because your brain compensated for the blue colour cast and effectively ‘saturated’ the warmer colours. Your camera cannot perform these tasks by itself, it needs some help from you, and by understanding the fundamentals of how light behaves underwater you will be able to take greater control of your underwater photography.

The behaviour of light underwater is unlike the behaviour of light on land. For starters, the density of water is 800 times that of air. Such is this density that we can compare a picture taken in 1 m of water with a picture on land taken at 800 m away.

1. As soon as light enters the water it also interacts with suspended particles,resulting in a loss of both colour and contrast.
2. Particulates and water molecules react with the light entering the sea,and it immediately begins to be absorbed.
3. Red goes first, then orange and yellow, until only green and blue are left. So rapid is the loss of red that within half a metre of the surface those red swimming shorts are muted and dull.
4. Even in the best imaginable visibility, particulates are suspended in the water column. In a typical tropical diving destination with good visibility,these particulates tend to reflect and scatter light as they move through the water. Whilst you can reduce their effects, you can never eliminate them entirely.

It is also important for the underwater photographer to recognise that:

1. The conditions on the surface have an effect on how light passes through the water.
2. Calm seas allow more light to pass through whilst a choppy sea reflects light.
3. The position of the sun in the sky and the time of day also have an effect on the amount of light entering the water.
4. When the sun is high in the sky over a flat calm sea, most of the sun’s rays pass through the surface. As the sun arcs closer to the horizon the light loss due to the angle of refraction against the water surface increases dramatically.

The light which does penetrate at these times is usually soft and diffused and I find it the most inspiring and magical time of day to take natural light photos underwater, although if you want to take pictures when the sun is high in the sky the best lighting conditions are between 1000 and 1400 hrs.

Noted:
This article took from The Underwater Photographer by Martin Edge.
If you want read more just visit http://focalpress.insidethecover.com/searchbook.jsp?isbn=IDGQFAU4063866 for online reading or buy this book directly from Amazon.
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