Depth of Field and How It Affects Your Underwater Photography

Depth of field is one of the most important concepts in photography. After exposure, it has the greatest amount of influence on an image. What it does is give depth to two dimensional images. Here's how it works:

Depth of Field

When focusing through a camera lens, you will find that there is no absolute point where an image goes from being sharp to being a blur. Instead, this happens gradually. You might choose a lens where the subject looks very sharp when he's fifteen feet away. But, an object that's three feet behind him is slightly soft, and an object that's ten feet behind that is a blur. That same effect also happens to objects that are in the foreground of the subject. Something three feet in front of him will look soft, while something ten feet in front of that is a blue. That's how depth of field works.

Depth of field can be broken down into two categories: shallow and deep. Deep depth of field refers to a DOF that is very gradual over a long distance. You'll still be able to make out an object that is ten feet behind the subject, even though it may be a little burry in deep depth of field. Shallow refers to a DOF that is very short. An object that is ten feet behind the subject will be a complete blur in shallow depth of field.

Underwater Photography

Underwater photography follows much different rules than what we're used to when shooting on dry land. That's because water has a huge effect on the light that penetrates trough it. Light is made up of different colors and water absorbs most of them quickly, leaving us with a dark blue light. In fact, it is difficult to tell the distinction of objects that are a few feet away from you underwater.

If you want to see something vividly, then you need to get very close to it. This makes underwater photography very similar to macro photography. Since you can only see a few feet behind your subject before everything becomes indistinct, you need to use lenses that produce a shallow depth of field to create a layered image. 

Macro Lenses

Because you need to get close to the subject in underwater photography, macro lenses are probably the best choice to use. They produce a very shallow depth of field. However, you need to be very careful in your selection. You want something that doesn't have too shallow of a depth of field. After all, you're shooting marine life, and you don't want your photos to come out blurry because the fish moved an inch.

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