Aperture & Shutter Speed when underwater

Aperture

Aperture in the opening of the lenses. To understand aperture think of aperture as a water tap, the more you open the tap the faster the water flows. To understand shutter speed think of the shutter speed as how long you leave the tap open.

Like the tap that controls the water flow, the lenses act in the same way. The aperture decides how much the shutter will open and the shutter speed setting controls how long the shutter will remain open for. Aperture setting is known as “f/stop”. The normal f/stop settings you would find on lenses are f/2.8, f/4, f/5.6. f8, f/11, f/16, f/22. The higher the f/stop number the smaller the opening, so less light is let through the lenses. So f/22 lets in very little light but f/2.8 lets in a lot of light.

Shutter Speed

Typical shutter speed settings are 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000. The smaller the number the faster the shutter speed. The general rule is that you should not set the shutter speed slower than 1/60 for underwater photography. The higher the number the faster the shutter speed.

Aperture and Depth of Field.

Not only does the aperture control the amount of light entering the camera, it also has an affect on the cameras focus. As you change the aperture the range of sharp focus (Depth of field) also changes. Depth of field is how much of the scene, from front to back is in or out of focus. The higher the f/stop the greater the depth of field,  the lower the f/stop (larger aperture) the less the depth of field.

Underwater you typically try to get the greater depth of field by using the smaller aperture (highest f/stop) for correct exposure.

Right Exposure

This is the relationship between aperture and shutter speed. Exposure is the total amount of light that reaches the film through the combination of aperture and shutter speed. By changing the shutter speed or aperture even one position you can either double or half the light reaching the film. Changing the aperture from f/8 to f/11 halves the light that enters the camera. Changing the shutter speed from 1/60 to 1/30 doubles how long the shutter will stay open for. So by controlling the shutter speed and aperture you control the exposure.