A good understanding of ‘Depth of field’ is essential to being able to take good photographs. However, this is a topic that often confuses a lot of photographers and while one can find many tutorials out there, the explanations are often very technical and make for daunting reading.
We will take a more practical approach to this subject. We will try to explain what depth of field is, how you can achieve it, and how and when to use it in your photographs; and we will try to do all of this while keeping things as non-technical as possible.
Before we proceed we are quickly going to remind you of some very basic terms in photography, that are essential to being able to understand ‘Depth of Field’.
Exposure: This is the amount of light received by the film or sensor, when you take a photograph.
The amount of light entering the camera is controlled by two things: the shutter speed, and the aperture.
Shutter speed: This determines how long the shutter remains open, and therefore how long the film or sensor is exposed to light.
Shutterspeeds are usually expressed either as:
1) fractions of a second, eg: 1/2s, 1/4s, 1/8s or even 1/4000s or
2) for longer exposures, in seconds. eg: 30s, 15s, 4s, 2s, 1s.
A longer shutter speed, like 1/2s, lets more light enter the camera than a shorter one, like 1/8s.
Aperture: The aperture is the size of the hole in the lens, that allows light to enter the camera. The bigger the hole, the more light enters the camera, and vice versa.
Aperture sizes are expressed in f-stops, which are denominators of a fraction. So f/8 is actually 1/8, and f/4 is 1/4. And since these are fractions, f/4 is larger than f/8, and therefore f/4 lets more light enter the camera than f/8.
Each next f/stop (aperture) setting reduces the amount of light entering the camera by half. We can use the terms f/stop and aperture interchangeably as for our purposes they mean the same thing. The larger the number, the smaller the aperture, the smaller the number, the larger the aperture, and, the larger the aperture, the more light enters the camera.
Depth of Field and is one of the most important concepts of modern photography. It originates from the very fabric of a camera and its optics. When you take a photograph, the optical system on your camera has to focus on a subject. This is either done automatically (with Auto Focus) or manually (with Manual Focus) but always consists in selecting a specific distance for the lens to adjust to.
The effect of focusing is that all the objects located at exactly the focus distance away from the camera, will appear perfectly sharp in the final picture.
On the other hand objects that are located in front of and behind the focus distance, will gradually appear out of focus.
It is also important to understand that focusing works according to the distance from the camera to the subject.
You cannot focus on the left part of a scene and leave the right part blurry, but you can focus on something at a certain distance from the camera and leave everything else blurry. For example, you can focus on the foreground and leave the background blurry.
The distance in front of and behind the focusing point, in which everything appears to be “acceptably sharp”, is referred to as the depth of field.
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This article is an excerpt from Complete Technical Photography Manual
(for any camera and any photographer!)
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