Many beginner, and even hobbyist, photographers see the images of professionals, with their nicely blurred backgrounds, and wonder how to create that same look in their photos. The technique is quite easy, actually, and only requires three steps to learn.
Before explaining the three steps, it’s important to understand that a blurry background is more than one not in focus. It’s the quality of the blurriness that counts and that quality is known as “bokeh.” Bokeh refers to the condition, or impression, of the areas of a photo that are not in focus. It doesn’t measure the degree to which these areas are not in focus. Instead, it is the nature, or the quality, of the blur of the background.
At a scientific level, light waves enter your lens and camera and strike the sensor. Light reflected from areas of a photo that register on the sensor as a single point causes those areas to appear in focus. When the focus point is in front of or “behind” the sensor, then what registers on the sensor is a circle. It is a cross-section of the cone of light that narrows to a single point.
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No lens is “perfect,” in that any of them will have distorting properties, such as spherical aberration. It’s this imperfection that creates what is known as correct bokeh, which is when the border of the circle of light waves striking the sensor is fuzzy. You can read more about the scientific explanation of bokeh and spherical aberration in the PhotographyTalk article link below.
Professionals know that controlling bokeh, or the quality of the background blur, is extremely important for outdoors portraits and sports, wildlife and action and macro photography. With the correct background blur, your in-focus subject seems to pop from the background and your images have more three-dimensionality. If you’re shooting sports in a stadium with a background of people, for example, then you want it sufficiently not in focus, so the athlete or athletes can be easily and quickly distinguished from the sea of faces and bodies behind them. Even a casual portrait takes on a professional quality when you know how to control the background blur.
To create pleasing and professional-looking blurred backgrounds, you must start with a professional camera, a DSLR. Compact cameras are limited in their capability to control bokeh, so you won’t achieve the best bokeh possible even with the latest models.
Step #1: Use the longest focal length of your lens. If you bought your DSLR camera as a kit with a lens included, then it is typically an 18–55mm. You can create good background blur with the 55mm focal length of this lens, but it will be even better when you use a lens with a much longer focal length, such as 200mm to 300mm. If you’re photographing portraits, however, then you’ll want to choose a focal length in the 85mm to 135mm range, which is just enough telephoto focal length to avoid any distortions of the person’s body or facial features.
Step #2: Compose your image, so there is a maximum amount of distance between your subject and the background. Returning to the scientific explanation of light above, the farther the background, the fuzzier will be the borders of the circles of light that strike your camera’s sensor.
Step #3: Select the smallest f/stop number, or the widest aperture, of the focal length of the lens you are using. This is why many professional portrait photographers use fixed focal length lenses, such as a 85mm, instead of a zoom lens. Some 85mm lenses have very wide apertures at f/1.8, which allow more light waves to enter the lens than zoom lenses. Their widest aperture may be only f/3.5, f/4 or even f/5.6. With more light waves entering the lens, more of them enter near the edges of the glass elements. Because of spherical aberration, these light waves will focus shorter than those that come straight through the center of the lens (and elements). Again, this lens imperfection helps to make the background blur more pleasing.
You may have realized that the other photography concept that is being described by these three steps is depth of field. Focal length of the lens, the space between the subject and background and the widest aperture are the same techniques that are used to control depth of field.
Photo copyright PhotographyTalk member Delayne Martinez
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