Depth of Field - One of the most important elements in photography.

Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. A preferred selection Depth of field (DOF) in a focused subject in an image can be quite subjective. It is all a matter of personal preference when trying to determine the appropriate use of DOF to enhance an effect in a photograph. 

Quick Reference Guide: Depth of field is governed by three factors: aperture, lens focal length and shooting distance. 

1. The smaller the aperture, the deeper the depth of field (the other two factors remaining the same). For example, if the lens focal length and the shooting distance stay the same, the depth of field is much deeper at f/16 than at f/1.4.
2. The shorter the lens focal length, the deeper the depth of field (the other two factors remaining the same). For example, comparing a 28mm lens with a 50mm lens at the same aperture and shooting distance, depth of field is deeper with the 28mm lens..
3. The greater the shooting distance, the deeper the depth of field. i.e. other two factors remaining the same). For example, if the subject is photographed from three and then from seven meters away, the zone of sharpness in the foreground and background is greater at seven meters.

Another characteristic of depth of field is that it is generally deeper in the background than in the foreground.

A typical example of a photo with shallow depth of field control. Only the main subject of interest is enhanced by throwing other elements out of focus.

 Another example of a shallow depth of field effect for close up as the distracting background is "thrown" out of focus to draw the viewer's attention to the main subject. The nearer of the subject in focus to your camera, depth of field will be more "shallow".

This is the OPPOSITE. Maximum depth of field is required to show the details of the scene that attracted my interest and so, if I want to show the entire scope of the scene from NEAR to FAR in sharp focus. A smaller aperture is used along with a 28mm wide angle lens to achieve the objective.

 It works on other usage such as dealing with scenic, candid, portraiture or even street photography.
Here is another example of smaller aperture is used on the lens section for MAXIMUM depth of field to ensure all the elements are in focus.

 One of the most used application is using Depth of Field control for portraiture photography. A clever photographer would use Depth of Field intelligently to emphasize a specific effect of the main subject of interest (in this case, the model) by limiting DOF away from confusing background via use of a larger aperture and/or using a smaller aperture to enhance the visual with pin sharp details from near to far (such as scenic, travel , landscape etc.). 

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