When you are new to photography, there are tons of things to think about when you're taking a photo. The shutter speed, the aperture, light, what you had for breakfast, etc. Literally tons of things. One of the more misunderstood terms is depth of field, or DoF. You may have heard the term depth of field, but if you are new to photography you may not yet be taking advantage of how it can enhance your photos. A basic definition of depth of field is: the zone of acceptable sharpness within a photo that will appear in focus. In every picture there is a certain area of your image in front of, and behind the subject that will appear in focus.
This zone will vary from photo to photo. Some images may have very small zones of focus which is called shallow depth of field. Others may have a very large zone of focus which is called deep depth of field. Three main factors that will affect how you control thedepth of field of your images are: aperture (f-stop), distance from the subject to the camera, and focal length of the lens on your camera. Here are some explanations and answers to other common questions concerning depth of field.
How does aperture control depth of field?
We talked about aperture in a previous post. If you forgot, or never read it, use the little search box in the upper right corner of this page and search for "aperture." Anyway, aperture refers to the access given to light from the lens to the camera sensors. The size of your aperture (the diameter of the hole through which light enters the camera) controls the amount of light entering your lens. Using the aperture (f-stop) of your lens is the simplest way to control your depth of field as you set up your shot.
Large aperture = Small f-number = Shallow (small) depth of field
Small aperture = Larger f-number = Deeper (larger) depth of field
I know this can sound confusing. Large things equal small numbers and vice versa. WTF? Just remember that the lower your f-number, the smaller your depth of field. Likewise, the higher your f-number, the larger your depth of field. For example, using a setting of f/2.8 will produce a very shallow depth of field while f/11 will produce a deeper DoF. If you're not totally confused now, read on.
Now what about focal length?
Focal Length refers to the capability of a lens to magnify the image of a distant subject. This can get crazy complicated, but the simple answer is that the longer you set your focal length the shallower the depth of field. Come on, that one is pretty easy, right? At least easier than that DoF stuff above.
Wait, distance controls depth of field too?
The closer your subject is to the camera, the shallower your depth of field becomes. Therefore, moving further away from your subject will deepen your depth of field.
So when should I use a shallow depth of field?
Using a shallow depth of field is a good way to make your subject stand out from its background and is great for portrait photography. Shallow DoF can also be useful anytime you want the subject to stand out from its surroundings, like wildlife shots. This is also useful because many wildlife photo opportunities are low light situations, and increasing your aperture size will give you more light. Shallow depth of field is also very often used in sports photography, where many times you want to separate the athlete from the background to bring attention to them. The result of this should also help give you a fast enough shutter speed to freeze the action.
In this example, notice that the eyes are totally sharp and in focus? That's where I wanted focus... for the eyes to be sharp. However, the background right behind her is soft and out of focus. That's a shallow depth of field.
Okay, I think I got it, so when should I use a deep depth of field?
Easy... Landscapes, period. Okay, not period. There are tones of examples where a deep depth of field would make sense that are not landscapes, but in general... landscapes.
Notice that everything is in focus here... from the front of the image all the way to the back... miles away. that's a deep depth of field.
Hope that helps. It's a concept that took me a while to understand, but once I did, I feel like i immediately became a better photographer. If nothing else, when you're at a dinner party, talking about DoF will really make people think you know what you're talking about. Try it, I promise it works.