Exposure is the total amount of light the camera lets in for any shot that you take. It is the light falling on the photographic medium while taking a photograph. Exposure is one of the most important techniques which should be mastered by an underwater photographer. Exposure adjustment controls the light intensity of the image subject and adjusts it to fall on the appropriate region to a yield a desired exposure.
Exposure adjustment is very crucial in underwater photography. This is because of the fact that there are two sources of light underwater. The first source is the flash and the second is the sunlight penetrating down into the water surface. One can control the exposure by adjusting the exposure value (EV) settings which is present on the cameras. A negative EV value will make the image darker by adjusting less light generation on the image whereas a positive EV value will generate more light and hence, the photo will be lighter.
In underwater photography correct exposure settings are a must. In overexposed images, there is a loss of highlight as all the bright parts turn out white whereas in underexposed images there is a loss of detail due to darkness known as blocked up shadows. Some cameras have an automatic exposure that automatically adjusts exposure settings of the subject. This is also known as through-the-lens exposure meter (TTL). In manual exposure the photographer himself has to adjust lens aperture, shutter speed, ISO to achieve the desired exposure effects. In multiple exposure technique, a single photograph is presented by combining two or more exposure effects.
In manual exposure settings, if one slows down the shutter speed, the aperture and ISO will be larger and hence the exposure will be brighter. There is a jargon known as “stop”. One stop brighter picture means to allow twice as much light whereas a stop darker means to allow half as much light.
Manual exposure settings are more reliable in underwater photography as matrix metering and automatic exposure are inconsistent. One needs to set everything correct – shutter speed, ISO, aperture. When changed one, you must compensate the other; this will give a correct exposure setting.