The Physics of Underwater Photography
This entry was posted on 19th March 2015.
waterproof housing. Water pressure is such that at only ten-metres deep it’s twice air pressure at the surface and much more as you go deeper so designers of housings take that into account. However, there is much more to underwater photography than simply keeping the camera dry and the same rules apply even if you have the very best kit. Photography is all about light and light acts in a different way in water to the way it does in air. For a start, water is never as clear as air. If you had 30-metres of visibility under water it would seem gin-clear yet the same visibility on a motorway would see you driving very slowly. It’s all about turbidity. Water is full of detritus and tiny life-forms. The secret to getting clear sharp pictures is to reduce the amount of water between your camera and your subject, to get as close as possible. Water also absorbs light but it absorbs light selectively. The longer wavelengths of light, the reds and the greens, get filtered out within only a few metres from the surface so that the brightest daylight looks blue under water. You can make the most of what red and green light gets through by filtering out some of the blue with a reddish filter or by repeatedly white-balancing your camera as you find yourself at different depths. You can take some portable white light with you in the form of an underwater flashgun (or strobe light) for stills or a bright video light for movies. However, remember that the light from these is affected in the same way and the range of such accessories is limited, possibly to less than two metres, so you still need to get close to your subject. At the same time you need to position these lights well away from the camera’s lens axis or they will simply light up all that detritus in the water and give you a very messy result. We call it ‘backscatter’. Mounting a flash or light on the end of an accessory arm does the trick but for convenience sake we normally have this attached to the camera housing via a suitable tray and manipulate the light via a series of one-inch ball joints and clamps. Ocean Leisure Cameras stocks a vast array of these to solve every mounting problem whether it be for a GoPro, for a top-of-the-range DSLR camera rig, or for something in between. Light is refracted when it passes from water into air through a flat glass camera front so that things appear at least one-third closer. It effectively makes your standard camera lens slightly telephoto. So having got close to our subject, we might find that we cannot include all of it in the shot. This is where a wide-angle lens comes into play. Under water, wide-angle lenses are used differently to the way they are used on land. They allow the camera to come close to the subject with the minimum of water between them, while at the same time restoring the image size. A dome port combined with a wide-angle lens or a compact camera’s zoom lens at its widest setting will restore the angle of view by reducing the amount of light refraction. These are available to fit some compact camera housings as well as housings for cameras with interchangeable lenses. Many underwater photographers start off by concentrating on macro subjects. A macro lens allows you to get very close indeed to the smallest of subjects and by using a flashgun on a mounting-arm, you take in with you your own ready-made mini studio set-up. Good results are assured because as your lens gets very close there is so little water to contend with. Flat housing ports help in this case because the refraction of light helps you stand off from your subject so that you can light it more easily. In summary, you need to prevent water ingress to your camera, you need to make the most of the full spectrum of natural light that penetrates the water, you need to avoid lighting up the turbidity of the water and, by getting as close as possible to your subject, you can reduce the effects of the poor optical quality of the water. The people working at Ocean Leisure Cameras can provide you with everything you need to achieve that. You just need to perfect your diving skills so that they become second nature while you take pictures or record video.When it comes to water everyone realises that to get your camera wet spells disaster. It’s either got to be designed to be waterproof or it must be enclosed in a