As a beginner photographer you may have been introduced to the term depth of field. This is one of those terms that you are likely going to hear quite a lot and will deal with regularly in your photograph. Playing with depth of field, no doubt, will become an important part of your photography.
Definition and types
Depth of field denotes the extent of the frame that is in focus. It could either be shallow or large depending on several attributes. Let’s say you are looking at a landscape image and the image has everything in sharp focus. This is an example of large depth of field. As you can imagine a large depth of field is used mostly for shooting nature photography, chiefly landscapes, as well as for journalistic style street photography. These type of photos require everything to be in focus.
Again, let’s say, you are looking at a portrait image. The subject’s face, and more specifically the eyes are in sharp focus whereas most of the foreground and the background are out of focus. This is an example of shallow depth of field. Shallow depth of field is used frequently in portrait, wildlife, flower and product photography.
Attributes to depth of field
There are a number of attributes that control this particular aspect of your imagery. They include not only the aperture value that you are using but also the camera sensor size as well as the focal length of the lens.
The F-number, very loosely, denotes the aperture that you are using. The actual definition is a relationship between the focal length and the opening of the lens. F-number is expressed in fractions such as f/2, f/4, f/5.6 and so on. Wider the aperture (smaller f-number), smaller is the area of the frame that is going to be in focus and thereby narrower the depth of field. On the flip side if the f-number is larger, depth of field becomes larger as well.
Sensor size has a major influence on the depth of field. Let’s say you are shooting with two cameras, one a full-frame 35mm and the other an APS-C DSLR. You are trying to compose the same shot with the same lens set to the same aperture. With the APS-C camera you will have to step back a few paces in order to capture the same composition. This happens because the smaller sensor effectively only sees a small section of the image coming through the lens. When you step back, automatically the depth of field increases. This is the opposite when you shoot with a full-frame 35mm sensor.
All things remaining the same, focal length of the lens also is a major contributor to depth of field. A telephoto lens, say 300mm will produce a shallower depth of field compared to a 200m lens. That is exactly why landscape photographers prefers to shoot with a wide angle lens. Alternatively, when you need maximum subject separation from the background a telephoto lens will give you better results. Speaking of telephoto lenses, they also do something else and that is to pull the background closer to the subject, a phenomenon known as background compression.
Videos on Depth of Field
We found a couple of videos on depth-of-field you’ll find are very informative. The first is from Dylan Bennett where he explains depth of field, how it works, and how to control it.
The second video on depth of field is from Mark Wallace for Adorama Photography TV.