If you are new to photography, you may have heard about something called depth of field, but you are not entirely sure what it means and how to take advantage of it. Depth of field is basically the zone of sharpness in a photograph. In every picture you take, a certain part of it is in focus and some of it is not. When the zone of sharpness is small, we call that a shallow depth of field. Otherwise, when a large part of the image is sharp, that is a large depth of field. Let’s take a look at the parameters that define the depth of field.
The aperture as a regulator of depth of field
By changing the aperture we are not only changing the amount of light that enters the camera, but we are also influencing the sharpness of a photograph. A low f-stop, like f/2.8 means that the aperture is more open than with a larger f-stop, like f/11. Coincidentally, a low f-stop will allow more light to enter the camera. By controlling the aperture, a photographer can utilize the depth of field to emphasize certain parts of an image. The larger the f-stop number – the larger the depth of field.
The photograph above was taken with an aperture value of f/2.8. You can see that only the eyes of the dog are sharp and the other parts of the image have gone blurry. Using low f-stops can be very useful when you want to really emphasize one particular subject. Knowing what parts of the image you should keep sharp and what parts you want out of focus is a great tool you can use to your advantage if you want to produce outstanding images.
On the other hand, when you are taking pictures of landscapes, like the photograph above, preferably you would keep most of the image sharp. That can be accomplished with a higher f-stop number. This particular image was taken with an aperture value of f/11, which is enough for the depth of field to span from the railroad tracks in front, to the statue that can be seen in the distance.
Another parameter that defines the depth of field in a photograph is the focal length of the lens you are using. Longer lenses produce much more blur than wide angle lenses. In other words, the same aperture value combined with a lens with a larger focal length means a bigger opening. A 100mm lens with an f/2 has a bigger aperture opening than a lens with 50mm focal length, also with an f/2.
Depth of field is not defined only by the aperture value and focal length, but also by the distance between the camera and the subject. Here, there is a simple rule: the shorter the distance between the lens and the focused subject, the more out of focus the rest of the photograph will be. The larger the distance between the camera and the subject is, the bigger the depth of field.
As you can see by now, there are a number of parameters that influence the depth of field in photography. Once you’ve got them down, you will see that they are not as intimidating as they sound at first. Trial and error is the best learning tool, so don’t be discouraged if you don’t immediately master them – try again!