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Natural light and visibility

30-feet deep is about the natural light limit.


Electronic flash is essential in deep water. Photo by Tom Sheldon.
Electronic flash is essential in deep water. Photo by Tom Sheldon.

The amount of ambient light drops off with depth. In fact, quite a lot of sunlight is lost right off the bat by reflection off the water’s surface, especially when the surface is rough. The further below the surface, the less natural light there is, making electronic flash necessary for any photography past a certain depth, generally below 30-feet (about 10 meters) in clear water.

DEALING WITH MURKINESS

The water's murkiness (the amount of minute particles held in suspension) contributes to reducing available light by its light-scattering characteristic.

The most common solution to overcoming the effects of murkiness is to reduce the volume of water between the lens and the subject – that is, to get closer and fill the frame. A handy rule of thumb governing how close you must be to achieve a clear image in existing light is to shoot at one-fifth of the overall visibility distance. This means if overall visibility is 25 feet, your lens should be no more than 5-feet away from the subject. (Some underwater photographers suggest that a shooting distance of one-third or one-fourth of the overall visibility distance is adequate for good results - that is, about 6 to 8-feet from the subject if visibility is 25 feet. The closer you are, the less water there is between you and your subject, resulting in a clearer image.)


WATER ABSORBS LIGHT PROGRESSIVELY

A further complication of underwater photography relates to water’s selectivity in absorbing light’s wavelengths, with shorter red wavelengths from sunlight being the first to go, at around 20 to 25-feet below the surface, where red subjects appear dark-brown or black. Photographs begin to take on a blue cast at depths of just a few feet.

Although the sun can be seen penetrating the water, its light alone would have been insufficient for this image. Photo by Tom Sheldon.
Although the sun can be seen penetrating the water, its light alone would have been insufficient for this image. Photo by Tom Sheldon.

Fortunately, much marine life can be photographed under natural light in relatively-shallow waters. Photo of a crimson sea anemone entrapping a blood starfish by Tom Sheldon.
Fortunately, much marine life can be photographed under natural light in relatively-shallow waters. Photo of a crimson sea anemone entrapping a blood starfish by Tom Sheldon.

Other colors are progressively absorbed at depths in feet of about 35 (orange), 65 (yellow), 75 (green), and 90 (blue). At depths below 100-feet, there is no natural light visible in any wavelength.

If you are bringing colored materials with you to depths where colors become absorbed, the materials can still be identified by their colors if they have been treated with fluorescent dyes, which retain their particular hues after all normal colors have lost theirs.


THE EFFECT OF SURFACE CONDITIONS ON AVAILABLE LIGHT

Visibility is also affected by conditions above the surface of the water. The position of the sun, for instance, is critical. The best light for underwater pictures occurs when the sun is almost or directly overhead, between mid-morning and mid-afternoon. This is in direct contrast to the ideal natural lighting for aerial and most other forms of photography. The sun has a lesser volume of water to travel through when it is directly overhead than when its rays penetrate at the more oblique angles associated with early morning and late afternoon.

Another surface consideration relates to atmospheric conditions. If the weather is overcast or if the sea is rough, less light will penetrate. A profusion of air bubbles near the surface or sediment stirred up by waves will scatter light.

Natural light falls off quickly as you go deeper, even in the clearest water.
Natural light falls off quickly as you go deeper, even in the clearest water.

As depth increases, unfiltered pictures have an increasingly stronger blue cast.
As depth increases, unfiltered pictures have an increasingly stronger blue cast.

STAY CLOSE TO THE SURFACE FOR NATURAL LIGHT COLOR PHOTOGRAPHY

The result of all this is that underwater color photography by natural light is only practical relatively near to the surface (no deeper than 30-feet in ideal conditions), and unfiltered images will have an increasingly-stronger blue cast as depth increases.

One positive consideration is that there is an abundance of marine life in shallow water, and many interesting underwater pictures can be taken in water as shallow as a few feet.

In clear water with the sun directly overhead, you can take black and white pictures in depths as low as 85-feet.


Artificial light is essential in the deep.
Artificial light is essential in the deep.