Mostly when a photographer talks about depth of field of an image is they’re referring to how much of the picture they choose to have in focus. By focusing how much depth of field to have in your image you will have the viewer’s attention in a place. Depth of field is controlled by changing the aperture setting on your camera. The first rule in depth of field is the larger the aperture, the shallower you depth of field will be. There are times when you’ll want to ensure a deep depth of field.

When to use a wide or narrow aperture is first as wide apertures let in more light than narrow ones. A portrait photographer would typically use a wide aperture of f/1.8 so that all the focus can be placed on their subject at the expense of details in the background. You might want to use a wider aperture when you want to isolate specific subjects from their backgrounds.