Depth Of Field Demystified in 4 Steps
Depth of field (DOF) is a zone of acceptable sharpness. In a landscape image you could have everything from touching distance to a mile away in sharpness. A wide DOF. In a close up of an insect perhaps only the insect’s eye is sharp. A shallow DOF.
Its your zone…
You control the zone of sharpness when you create a picture. When you select a lens, set its aperture and choose composition you are making choices that affect DOF. By controlling what is sharp and what is out of focus you are effectively telling the viewer:
“Hey look at this, this is the essence of the image I want you to see. The rest is decoration.”
A medium aperture of f8 cuts some of the light entering and deepens the field depth. A small aperture such as f16 lets in relatively little light and keeps everything from front to back quite sharp.
A shorter focal length has a wider depth of field. A longer focal length has a narrower DOF. That is why some wildlife photographers will deliberately stay back and use a longer lens to isolate the subject from its background.
Even if they can get close they’d rather use a longer zens to thrown the background out of focus and achieve a nice blur.
At the opposite extreme a wide angle lens gives a wide depth even at bigger apertures and can be chosen to show wildlife in its environment.
Two factors of distance affect DOF.
- The distance between you and the animal.
- The distance between the animal and the background.
In the robin photographs below, the same aperture was set but despite this the left one has a busy background while the right one has a softer background. This is because in the first example the robin is close to the leaves behind. In the second example the robin is on a branch placing it further from the other leaves.
This background distance is something to consider when planning your photograph.
Managing this combination of lens aperture, focal length and subject distance comes from experience. Once gained you’ll be able to use depth of field to control your images.