In our last shooting guide, we talked about the aesthetic beauty of bokeh. As you recall, you use a large aperture to create the shallow depth of field (DOF) that helps to create bokeh. In addition to creating lovely bokeh, aperture and depth of field can be used as a compositional technique to help lead the viewer’s eyes in the image.
There are three main ways aperture and depth of field can help you compose a better photo.
When you use a large aperture like f/2.8 or faster to selectively focus on one subject, you create a visual emphasis on that subject. When our eyes and brain sees a subject that is in focus against a blurry background, we tend to put the most importance to that sharply defined subject. This is great for portraits, sports, and macro photography, where you want to isolate the subject and make sure that the viewer’s eyes go to the subject first.
The most common use of shallow depth of field isolation is to have something in the foreground in focus and blur out the background. The foreground subject will pop out in the image. Just remember to have enough distance between the foreground subject and the background.
The second way you can compose with shallow depth of field is to isolate a subject that is further back in the plane of focus and blur out the foreground and/or background elements. This adds layers of depth to the image and places the visual importance further back in the image. Even though the foreground is closer to the camera, because it is blurred out, it is not as important the subject in focus.
Finally, you can also use the out-of-focus foreground element to frame the in-focus background subject. Work with your environment to see how you can create natural frames.
Generally, a lens with a longer focal-length and a large aperture will have an easier time in creating shallow DOF. That’s why photographers love portrait lenses like the Nikon 85mm f/1.4G and the Canon 85mm EF f/1.8 USM, as well as the classic 70-200mm f/2.8 zoom lenses from Nikon and Canon.
When you are shooting with a shallow DOF, be sure to use your depth of field preview button to check how much DOF you really have in your image, especially when you are not shooting
completely wide open on your aperture.
Using a small aperture to create great depth of field helps to create a story in layers within your image. You have a foreground story, followed by the middle ground, and concluding in the background. The environment becomes an integral part of the story, so be sure that you don’t have any extraneous objects in the composition that can distract the viewer.
Generally, when you are composing with deep DOF, it is better to use a wider angle lens and an aperture range between f/7 t f/13. This is because the wide angle lenses capture more of the environment that helps to tell the story.
To focus to infinity, it is generally acceptable to pick a point about 1/3 up in the plane of focus. This will maximize sharpness in front and behind that point. If your lens has a depth of field settings or distance settings, you can also use them to calculate how much of your image will be in focus.
Finally, when using a really small aperture like f/22, you do run the risk of diffraction, so pay attention to that. This is a phenomenon where light starts to bend around the small aperture opening and end up softening the image.
Deep depth of field via smaller apertures is typically used for environmental portraits, architectural, and landscape photography.
When the subject and the background are in the same or close to the same plane of focus, you want to use the sharpest aperture for the lens you are using. Majority of lenses are at their sharpest from f/8 to f/11. This is also known as the critical aperture.
Aperture and depth of field play an important part in photographic composition. You can either isolate your subject by using shallow depth of field or use the entire environment to add context to your subject by using a deep depth of field. When your subject and background are at or near the same plane of focus, use the critical aperture to get the sharpest image possible.