This is mostly an excuse for me to let y’all know there’s some pictures from Mexico up on Flickr now. But, for those too lazy to click, some thumbnails are below, and for the few that are actually interested, the below is a quick hash-up of what I learned on my underwater photography course over there.
The first problem, is backscatter: the diffuse reflection of light from impurities, such as sediment, micro-organisms or even just salty water. A big consideration, therefore, is to move without disturbing the bottom so as to avoid dirtying the water: this isn’t easy when the ground is sloped and you’re trying to get very close for a shot, or into a tight space. This can also be negated somewhat by trying to be as physically close to the object as possible, and using natural light where possible.
If some additional light is required, then an offset strobe is the option of choice. By keeping the strobe at a wide angle from the camera, subjects can be lit incidentally rather than directly, and both backscatter and overexposure can be tamed.
At depth or distance, colour becomes an issue too. Water is about 800 times denser than air, and absorbs light from the visible spectrum, starting from the lower end; so red is the first to go. You can either use a filter under the water, or try and Photoshop the light back in later, but this is pretty much always going to be a problem.
A final problem is that if you’re using an underwater camera case, and you try and take some photos at the surface afterwards, it’s a nightmare to clear the lens of water droplets. The textbook has no advice for that; maybe it’s in the advanced course.
Here’s some pics from our training: