Depth of Field And Focus Explained
When taking photos, it is important to keep in mind that what you see on your camera is not usually what the outcome will be. Most of the time, even if the scene appears sharp in all areas; the actual photo will show only a portion (or some portions) to be truly sharp. This is what the depth of field is all about.
Understanding the Depth of Field
The term depth of field refers to the range of distance in front of and behind objects in a photo or image that appears sharp. For example, when you take a photo of marching clowns in a parade, your main subjects are not the only ones that will appear sharp. Objects that are in between you and the subjects, and even those behind the marching clowns (like a cheering crowd, perhaps?) – will also appear sharp.
There is a specific area or zone that is covered by the depth of field and this is identified and controlled by three major factors.
The aperture, which is the opening of the lens, is used to determine the amount of light that goes through the lens and into the image sensor. Its size is identified by what is called f-stops, which is characterized by f/numbers. Small f/numbers are equal to large aperture sizes, while large f/numbers stand for smaller aperture sizes. The aperture size affects the depth of field of a scene.
For a wider depth of field, go for small aperture along with wide lens. Remember that the higher the number, the smaller the aperture. So the perfect examples for this would be f/16 and f/22. Since you might find it a little difficult to take steady shots in this environment, you should use a tripod to eliminate shaking and trembling.
If you want to focus your attention on just one (or a smaller) scene, use a large or wide aperture and long lens. This will render areas outside the depth of field out-of-focus. Good examples would be f/1.8, f/2 and f/3.5.
When you talk about how much a lens magnifies an image or a scene, you are referring to its focal length. This is also an important factor in controlling the depth of field.
If you choose to use wide angle lens, your depth of field will be wider or more extensive. Focusing is easier in a scenario like this.
If, however, you want a smaller or limited depth of field, you will need to use a telephoto lens or lens with longer focal length.
Focus Point or Focus Distance
How near or far your subject is to the camera will also help determine the depth of field.
If you are close to or near the subject, there will be a limited depth of field in the scene you are trying to capture. Most probably, the image will cover only the front and back portions of the scene.
The more distant you are from your subject, the wider or larger the depth of field. As a result, the depth of focus is shorter. When you talk about depth of focus, you are referring to the range of distance that your lens can be adjusted (either forward or backward) without ever affecting the focus of or on an object or subject.
The DOF Preview
As previously mentioned, what you will see through your lens and your camera’s viewfinder is usually not the exact image that is produced. Basically, you’ll see the same image on your viewfinder regardless of which f/number you used. This is why dSLR users take advantage of the DOF Preview feature of their cameras. This feature will bring the camera to the aperture you chose so that you will get a preview of the actual depth of field.
If you want to achieve almost-perfect depth of field, then you should definitely go for a camera with a DOF Preview.
Shallow Depth of Field
Shallow depth of field is another way of describing photos that were shot using a wider aperture. Thus, only a small portion of the scene is sharply focused.
A lot of photographers choose to go with a shallow depth of field because it allows them to achieve the best focus for cluttered backgrounds. With a shallow depth of field, there is selective focus, so your main subject is the one on central focus. For example, you’re shooting a child dancing in the street, oblivious to the people walking by. Though the scene will initially appear cluttered, by using a wide aperture number, you get to de-clutter and shift your focus only to the child. The objects in between you and the child will become out-of-focus.
Using shallow depth of field will help you create dream-like photos that often elicit dramatic responses from viewers.
To sum up how you can control depth of field on your photos, it is important to remember two things:
- For a limited depth of field, use a wide aperture and a longer focal length. Be sure to move as close as you can to your subject.
- For a wider depth of field, use a smaller aperture and shorter focal length (or telephoto lens). Then move as far away as you can from the subject.
When you manipulate the depth of field by adjusting the aperture, be sure to also change the shutter speed of your camera. This will help you come up with good photos despite the changes resulting from the manipulation of the DOF.
As in everything else in photography, practice will help you achieve good depth of field. You’ll learn to adjust according to your needs once you’ve mastered the techniques. Practice shooting scene with wide and limited depth of fields so you can compare and contrast. This is one way of determining which one is best for you (or your clients’ needs). Lastly, familiarize aperture size as you’ll need this to create sharp and well-focused photos that generate viewer interest.