Understanding the Factors that Affect Depth of Field
What is depth of field (DOF)
The simplest definition for depth of field is the area of your image that is in focus. More specifically, the distance between the nearest and the farthest object that are in focus. The shallowness of the depth of field depends of the f/stop also known as aperture, the focal length of the lens, the size of the camera sensor and distances between you, the subject and the background.
Aperture or also known as f stop
The first thing we are going to talk is the aperture value. What is aperture? Well, when you look at camera lens you are going to see a maximum aperture range for that lens. For example f/3.5 – 5.6. The main purpose of the lens is to collect light and deliver it to the camera sensor.
The aperture of a lens is the diameter of its opening. Aperture is expressed as a f/stop. The smaller the f/stop number (or f/value), the larger the lens opening (aperture). Depth of field depends of the size of the opening of the aperture. The larger the aperture opening is the more shallow the depth of field will be and opposite vice versa.
The next thing that defines depth of field is focal length. If you have zoom lens or two prime lenses that are different in focal length you can test this yourself. The basic idea is that the longer the focal length is, the shallow the depth of field will get. And of course, the opposite is true when we have short focal lengths. For example if you shoot something with a 50mm lens at f/2.8 and then shoot the same thing with 200mm lens at f/2.8 the difference in the depth of field is going to be dramatic.
Distance between the object and background
The final thing we are going to talk about today is the distance between the object we are shooting and the background. The further away the background is from the subject, the more blurred the background is going to be. For example, if we shoot a model that is standing 3 meters away from us and the background is 5 meters behind the model, the background will be sharper than if the background were further away.