Depth of Field (DOF) is the extent of the picture which is acceptably sharp. DOF is an important consideration in any type of photography and is creatively used to add depth, sense of dimension and perspective to the pictures. A number of parameters influence the extent of the DOF or sharpness in the image. In this article we shall be looking at how to create a deep Depth of Field or a shallow one to creatively enhance your pictures.
Aperture is the opening of the lens. It is the single mechanism that controls the entry of light into the lens and reaching the camera sensor. The aperture of the lens can be adjusted (along with the shutter speed) to control the amount of light that falls on the sensor. However, apart from controlling the amount of light, aperture also has an effect on the DOF.
DOF is expressed as ‘F’ / number such as f/4, f/5.6 and so on. Smaller the ‘F’ number, such as f/4 or f/2.8 and so on, smaller (or shallower) is the DOF. Alternatively, bigger the f/number such as f/5.6, f8 and so on, bigger is the DOF.
Look at the above picture. A small f-number has been used resulting in the foreground to be in focus whereas the background consisting of the street lights and the lights from oncoming vehicles to be blurred. This is a demonstration of how shallow DOF can be used in your photos.
Shallow DOF is used in a lot of situations, but they are particularly preferred by portrait, macro and flower photographers. In the subsequent photograph the dog is in sharp focus whereas the background is out of focus giving it a soft blur effect.
The main reason why the background is kept out of focus using the shallow DOF technique is to eliminate any uninteresting objects in the background. Let’s say a subject is standing against a wall and the wall is not exactly photogenic. The DOF can be reduced to focus on the subject and keeping the wall out of focus. However in this particular case the subject has to be at some distance from the wall for the later to be out of focus. In the subsequent paragraphs we shall find out how adjusting the distance between the subject and the background and the subject and the camera can alter the degree of out of focus effect.
A larger DOF is required when composing landscape pictures. Traditionally photographers have preferred using a small f/number something like f/8 or even f/11 to ensure that every bit of the frame is in sharp focus. The above landscape picture which has everything in focus demonstrates a perfect case of deep Depth of Field.
Deep Depth of Field has a particularly interesting use and that is in creating long exposure photos. Pictures of waterfall or sun-sets or sun-rise photos have often been taken using long shutter speeds to capture a misty effect of the water. Although Neutral Density filters or faders are used to perfect the shot, a smaller f-number assists in getting a larger DOF while allowing a longer exposure. The picture below highlights one such use.
2. Focal length
The focal length that you’re shooting at will have an impact on your Depth of Field. So if you’re using a 10mm lens e.g., you’re going to have a deep Depth of Field compared to if you’re using a 55mm. The more is the focal length of your lens going to be DOF will continue to get shallower and shallower.
3. Distance between the subject and the lens and the subject and the background
In the above picture, the subject is positioned very close to the lens. The closer the distance between the subject and the lens the shallower is the DOF and vice versa. The same is the case for the distance between the subject and the background. If they are very close together you’re going to get a deep Depth of Field or vice versa. In a previous example in this article, a reference was drawn to elaborate how a subject standing against an uninteresting wall was asked to step forward thereby decreasing the DOF and blurring out the wall.