Techniques
Stay Shallow
Water absorbs light starting with the lower energy wavelengths i.e. the red side of the visible colour spectrum. There are four primary causes for light and colour loss: diffusion, reflection, absorption and scattering. The deeper you dive, the more colour you loose beginning with the reds at around 10m and continuing with oranges, yellows and finally greens and blues at very deep water. Stay relatively shallow for more light, colour and dive time.
Please also check out the Colour Loss section on the Camera Settings Page.
Get Closer
Colour is also affected by the total distance light has to travel and not just depth. Furthermore, objects look closer and bigger underwater than they actually are. Get as close as you can to your subject to fill the frame and reduce distracting elements from your composition. Wide-angle lens allows you get as close as possible while still incorporating a wide coverage of the surroundings. The deeper you are or the farther you are from your subject, the bluer your image will be.
Aim Up
Shoot at an upward angle to make use of surface light. Try to avoid taking photos pointing at the sand. Sand underwater distortes the white balance settings of the camera and produces images where the whites are incorrect. Moreover, by shooting up you can achieve better separation of your subject from a distracting background.
Best Time of the Day
Only an average of 20 percent of sunlight reaches an approximate of 10 meters of water. Furthermore, maximum penetration occurs when light enters the water perpendicularly. The less the angle of penetration the less light is reflected off the water surface. When the sun is in the zenith meaning directly over head, the sunlights hit the water at a steep (near perpendicular) angle and more light penetrates the water. The best time of the day for underwater photography is when it is the brightest between 10am to 2pm.
Steady your Camera
The most common cause for blurry images is not focusing errors but failure to hold the camera still. Try and steady the camera while pressing the shutter. Good buoyancy skills can help with a steady camera.
Buoyancy Control
Larger camera systems can be very cumbersome, produce drag underwater and may interfere with your buoyancy. Do not dive under-weighted; adjust your BCD accordingly throughout your dive. You may get distracted while shooting away or you may use your air supply quicker with the extra equipment and drag in the water. When not taking photos, keep a check on your air supply, depth, buoyancy, dive time and maintain buddy contact.
Taking photos underwater can be very attention-oriented activity. Avoid contact with the bottom by maintaining neutral buoyancy and be aware of the position of your fins. In some cases you may choose to find a sandy patch on the bottom and kneel on your knees while taking the photos. The slower and more relaxed way you swim in the water, the easier it will be to approach your subjects without disturbing them or harming the underwater environment.
Environment and Conservation
When you pay attention to your buoyancy, you help with conservation of the underwater environment. Do not harass or stress the marine life in order to get a good shot.
Pre-Focus
Pre-focus means that you set the distance, aperture, strobe position, and optical viewer for a preset distance. It is sometimes much easier to move forward or backward from the subject until it comes into focus than trying to constantly adjusting your settings for every photo opportunity.