Aperture and Depth of Field

Depth of Field  is one of the most important aspects of photography. It can make the difference between a snapshot and a stunning image. However, many photographers have little or no idea of how to set their cameras for a desired Depth of Field effect. Aperture controls the depth of field.

When a lens is focused on an object, there is some distance in front of the object and some behind the object, which will also be acceptably sharp. A component of aperture is the depth of field and will allow you to create more dynamic photos.  Depth of field adds dimension to the photo by either blurring out the background and foreground or ensuring everything in the photo remains in focus. The size of the stop directly affects the depth of field.

The smaller the f-stop, the shallower the depth of field.  The means the foreground and background objects will be blurred.

Take a look at the picture of the puppy below.  Notice how the puppy's face is sharp and in focus. However the background and the areas of the rug in the background (farther from the puppy) and the foreground (closer than the subject) get blurrier the farther away they are from the main focus (the puppy's face). Portrait and macro photography usually use shallow depth of field. This tells us that this photos is a good example of shallow depth of field and the photo was taken with a small f-stop number.

When shooting a landscape, for example, you'll want as much of the photograph as possible to be in sharp focus, so larger depth of field is required.  The larger the f-stop, the deeper the depth of field.  These photos will have the foreground and background objects sharp and in focus. Landscape photos usually user a deep depth of field. Take a look at the example below.  The flowers, the hills and the mountain are all in sharp focus.  This tells us that this photo is a good example of deep depth of field and the photo was taken with a large f-stop number .

3 Factors that Control Depth of Field 

Focal length is a factor to the depth of field because it decreases as the lens' focal length increases. Thus, wide angle lenses (relative to film or sensor size) offer inherently more depth of field along the entire focal length while telephoto lenses (80 and longer ...as long as 600-1000mm) have less. A smaller aperture (larger f-stop number ) gives you a greater depth of field. This means that shooting at larger apertures like f/1.8 will make the background appear blurred, while using small apertures like f/16 or f/22 will result in a picture where much of the scene is in sharp focus.

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Great depth of field (resulting from using a small lens aperture, a wide angle lens, distant focusing, or a combination of these factors) is often used for the following types of subjects: - Landscapes, such as wide angle, general views. - Architecture, in which the foregrounds to buildings are important features. - Interiors, including nearby furniture and other objects, and far windows and similar features. As a byproduct, somewhat smaller apertures tend to reduce lens flare and improve lens performance ... some think that the smaller the aperture, like f16, f22, or f32 is the sharpest setting for most lenses, that is NOT the case ... for ultimate sharpness, a mid-range fstop setting like f8 is generally the best, according to scientific optical bench tests on various lenses.

Great depth of field (resulting from using a small lens aperture, a wide angle lens, distant focusing, or a combination of these factors) is often used for the following types of subjects: 

- Landscapes, such as wide angle, general views.
- Architecture, in which the foregrounds to buildings are important features.
- Interiors, including nearby furniture and other objects, and far windows and similar features.

Again, as a byproduct, somewhat smaller apertures tend to reduce lens flare and improve lens performance ... some think that the smaller the aperture, like f16, f22, or f32 is the sharpest setting for most lenses, that is NOT the case ... for ultimate sharpness, a mid-range setting like f8 is generally the best, according to scientific optical bench tests on various lenses.

A shallow depth of field (resulting from a wide lens aperture, a long focal length lens, focusing close up, or a combination of these) renders only a small portion of the image sharp, and is often used for: 

- Portraiture, to help concentrate viewer attention.
- Reducing the distraction from elements that cannot be removed from the lens's field of view.
- Isolating the subject from the distracting visual clutter of its surroundings.

How Do You Adjust the Depth of Field on Your Camera?

It's time to grab your camera.  Remember the Mode dial on your camera?

As was mentioned in a previous lesson, the Av button stands for Aperture Value. Turn the mode dial to Av.  Your camera will now make Aperture the primary factor in your exposure.  As the photography, you can now adjust the f-stop (eg. smaller for shallow depth of field) and the camera will automatically adjust the shutter speed to give it's best guess to achieve perfect exposure. 

Let's think about this for a minute.  If the aperture diaphragm opening is small the shutter will have to stay open a little longer.  If the aperture diaphragm opening is large the shutter will have to stay open a little shorter.  Refer back to your eyes.  If it's very dark outside, your pupils will open a little wider to allow more light in.

Depending on your make and model of camera the Av adjustment might be a dial or a button. Experiment a little or check your camera's manual.  Your f-stop will usually be on your LCD screen and of course will be indicated as such.  eg. f-22, f-8.   You can also see which f-stop was used after the photo has been taken.  Again, you may have to adjust the menu or display settings depending on your camera.  Can you tell which f-stop number is indicated on the camera in the photo below? If you think it's F-6.3 you're absolutely right!

Depth of Field and Aperture Summary

Some styles of photography require large DOF (and small Apertures). For example, in most landscape photography you'll see small aperture settings (large numbers) selected by photographers. This ensures that everything from the foreground to the horizon is relatively in focus.

On the other hand, when doing portrait photography it can be very handy to have your subject perfectly in focus but have a nice blurry background. This can ensure that your subject is the main focal point and that other elements in the shot are not distracting. In this case you'd choose a large aperture (small number) to ensure a shallow DOF.

Macro photographers tend to mainly use large apertures to ensure that the element of the subject that they are focusing on totally captures the attention of the viewer. The rest of the image is completely thrown out of focus so as not to distract the viewer.

The best way to understand aperture is to get your camera out and do some experimenting. You will get the chance to do this in the next section.

This concludes the Aperture and Depth of Field section.  Please proceed to the next section, where you will learn about  Practice Depth of Field.