When I told people I would be spending the rainy season in Bali, they asked weather I would be able to take good pictures once the visibility dropped. My answer was yes, no problem. Would a wedding photographer cancel a shoot because it rains? No they would just change their techniques to deal with the conditions. The same is true underwater.
What creates bad visibility?
To know how to shoot in difficult conditions you first need to fully understand them. The term visibility relates to how far a diver can see underwater, usually measured in feet or meters. Everyone has a different idea on what bad visibility is, usually determined by where they have dived before. For example, someone who has only dived in the UK may consider 10 meters to be good visibility. Compared to someone who is used to diving in more exotic locations like Indonesia or the Red Sea would consider 10 meter to be bad.
I have already hinted that rain could make the water murky. In fact, weather in general is usually the main factor affecting a sudden change in visibility. Wind and rain creates water movement which picks up particles from the bottom, suspending them in the water column. This water movement can come from waves, swell, currents or downhill flows, like in rivers. The more the water moves the more particles are picked up and the worse the water gets. Only once the water has stopped moving can those particles fall back down. Then the water will start to clear.
Adjusting your techniques.
There are three main things you need to adjust for:
- First get closer to your subject. If you can not see something clearly then neither will your camera. Details will get lost faster and often corals or divers further away will appear as shadowy shapes. You can use this to your advantage when shooting wide angle (sometimes shadowy shapes can look spooky or mysterious) But if you are expecting the visibility to be low then it would be best to put your macro lens on and just get close.
- Second Adjust your exposure. The particles in the water creates a cloud affect limiting the amount of sun light which can reach your camera. So increase your ISO, open your aperture wider, use longer shutter speeds, or introduce strobes. You may need to change a combination of these.
- Third Perfect your strobe angle. With a large number of particles floating around backscatter is a very prominent problem. Backscatter is when light from the strobe bounces off the particles and reflects back into the camera, creating lots of white dots, which can ruin a picture. The way to prevent this is to have the strobes far away from the lens and point out slightly. The strobes create a cone of light; you want just the edge of this cone to be touching your subject, then any particles between the lens and subject will not be hit by the strobe light and will remain dark.