Depth of field is the range of distance around the focal plane, which is acceptably sharp.
Factors affecting the depth of field are the camera and lens type, aperture and focus distance.
Depth of field is not an abrupt change, but a smooth gradual sharp to blurry transition, as can be seen in the photograph above. Everything in front or behind the focus plane begins to loose sharpness, even if it is not detectable by the camera or our eyes.
Depth of field should not be confused with Depth of Focus. Depth of Focus, or Focal Spread, describes the distance over which light is focused at the cameras sensor, as opposed to how much of the subject is in focus. It is important because it sets tolerances on how level the cameras sensor has to be in order to capture proper focus in all regions of the image.
Controlling Depth of Field
Aperture and focal distance are the two main factors affecting depth of field. As a general rule:
- Larger Apatures (smaller f-stop numbers e.g. f/2.8) will result in small depth of field.
- Close focal distance will result in small depth of field e.g. Macro.
- Smaller Apatures (larger f-stop numbers e.g. f/32) will result in a large depth of field.
- Large focal distance will result in large depth of field e.g. Wide-angle.
Uses of Depth of Field
Depending on what your subject is, depth of field can help you or hinder you. In macro photography, depth of field means that you only have a very small “sweet spot” for the subject, which means focus has to be perfect. In another example, if you are photographing a portrait of somebody, depth of field will make the person stand out from the background.
More
For more in depth (no pun intended!) information, have a look at Norman Koren’s photography site.
