Undestanding Depth of Field is one of the keys to mastering the basic photography composition techniques.
The camera lens focusses at a specific distance from the lens, however an area in the foreground and an area in the background remains in acceptable focus. This total distance of acceptable focus is called depth of field. It depends on 3 factors:
- Focal Length of the Lens: More the focal length less the depth. i.e. a wide lens has more depth of field than the normal lens which has more depth of field than a tele lens.
- Lens Aperture: Depth of field decreases with increasing aperture. At f5.8 the depth of field is less than f8. Rememer that the aperture or the lens opening has an inverse relation to the aperture f-number.
- Focussing Distance: A subject in focus will have less depth of field than another subject in focus that is further away from the camera.
Also the field of acceptable focus is more in the background than in the foreground, i.e the subject if focus is not halfway in the depth of field zone. Using the above factors to control the depth of field is an essential skill for a photographer. For creative impact the depth needs to be less or more depending on the type of photograph. For instance, portraits require less of field whereas landscapes require as much depth as you can get. And when doing macro photography, somethings it becomes a challenge to get as much depth as you want. It is not easy to know exactly how much the depth of field will be. Some lenses have a depth of field scale or a preview button but these are to be used for general idea. If you are new to the concept of depth of field, the only way to master it is to take photographs of the same scenes by varying the factors listed above and analysing the photos. Then it will make sense why different scenes require different depth of field and how to get the it just about right in a photograph.
