Depth of field is a big deal because it directly affects the composition, acceptability, desirability, and general artistry of your images.
Depth of field refers to the parts of the scene in focus in front of and behind the subject.
Sometimes you want the depth of field to be so shallow that the background is entirely blurred with no definition at all.
That directs a viewer’s attention where you want it.
Background vs. foreground
Out-of-focus backgrounds are not only acceptable, but often desirable.
However, out-of-focus foregrounds can be unattractive and even distracting.
For an out-of-focus foreground to look right, it should be just a blur of color.
Four factors when you shoot:
1. Lens focal length. The longer the focal length, the less depth of field in the image. On the other hand, as the focal length shortens, depth of field increases. Long telephotos have very shallow depth of field.
2. Lens aperture. As the lens closes down to a small opening, depth of field increases toward the maximum the lens can provide. When you choose to use large lens apertures, you lose depth of field.
3. Distance to the subject. When you move in close to a subject, such as when doing close-up or macro photography, or when you want to fill the frame with a small object, depth of field decreases. On the other hand, as you back away from the subject, depth of field increases.
4. In close-up or macro photography, placing the camera so its back is parallel to the subject, increases depth of field. When the camera back is slanted to the plane of the subject, depth of field is reduced.
There is a shot where you don't have to worry about depth of field. Everything will be in focus at any lens aperture when the elements in the scene are far away. Large lens apertures give you shallow depth of field. However, a wide-angle lens has tremendous depth of field so more of the picture comes into focus.
As usual, a tripod helps
When you close the lens down to use a small aperture, less light enters the camera. The lightmeter must compensate for the light loss to maintain a correct exposure. The shutter speed becomes longer. A tripod steadies the camera, reducing the possibility of blurring images of stationary objects.
When you move in very close to small objects in macro photography, depth of field becomes limited by the shooting distance between the subject and lens. Small apertures often are used in close-up photography to recover that loss in depth of field. That forces the use slow shutter speeds. Use a tripod when doing macro photography. Otherwise, the photos will be blurred or else have very shallow depth of field.
The same is true when using a long telephoto lens. Any movement will be magnified in the lens and a tripod would stabilize the camera and lens for a sharp image.
