What is Depth of Field – Chapter 2
“The choice of aperture provides the control on the depth of field (DoF) in an image”.
This brings us to the concept called depth of field.
What is Depth of Field?
Depth of field is the area in focus; in front of and behind your focus point in the image.
A little confusing? Have a look at the image below.
You can see the subject in focus and the background is blurred or out of focus. Thus, the area in focus is the DoF rest is blurred.
The effect of Aperture choice on Depth of Field
The larger the aperture the shallow the DoF and similarly, the smaller the aperture the larger the DoF. In Aperture Priority you can throw the background or foreground out of focus based on your Aperture setting. This implies that you’ll have a shallow DoF at an aperture of f/2.8 and have a large DoF at say f/5.6 and even larger DoF at f/11.
Factors affecting the Depth of Field
Along with the choice of aperture there are other factors that affect the DoF in an image.
1. Camera to Subject Distance
Depth of field is also determined by how close the camera is from the subject. The closer the camera with a given Aperture setting the the shallower the DoF. The farther the camera moves (with the same aperture setting) the larger the DoF is. This implies that you’ll have shallower depth of field at say an aperture setting of f/4 at at a subject distance of 5 feet from the subject vis-a-vis at a subject distance of 10 feet at the same aperture of f/4.
2. Choice of Focal Length of the Lens
DoF is shallow for a given distance between subject to camera for a telephoto lens. DoF is large for a given distance between subject to camera for a wide angle lens. Thus with a 200mm telephoto lens at an aperture setting of f/4 with a subject say 5 feet from the camera, the DoF will be shallower than a 35mm wide angle lens at similar aperture setting of f/4 and a similar subject distance of 5 feet.