Selective Focus and Depth Of Field
Selective Focus is a great technique that directs the viewer to the primary focal point or subject within the photo.
Rather than being drawn to similar objects, which might otherwise compete for attention with the primary focal point within your photo, selective focus allows you to ensure the viewer’s attention is placed exactly where you want it to be.
Selective Focus at Versailles
I made the above photo of the beautiful, sunlit flowers in the gardens of Versailles on a warm summer's day to demonstrate the selective focus technique.
Let's look at how to apply the selective focus technique to your images.
Ensure the lens is focused on your primary focal point. You can employ focus peeking, if your camera incorporates that feature, to achieve more critical focus on stationary subjects.
Employ a shallow depth of field to de-emphasize the surroundings and, thereby, make your primary focal point stand out against a de-focused background.
How To Create A Shallow Depth Of Field
Folks often complain to me that they're unable to blur the surroundings to the degree they'd like to. The reasons for this are a little complex, although the solution is, sometimes, quite straightforward.
The three factors that determine depth of field are as follows:
Lens Focal Length
Camera to subject distance
Let's examine each of these factors, one at a time.
Aperture and Shallow Depth Of Field
A physically wide aperture, such as f/3.5 (or wider), will produce a relatively shallow depth of field.
The smaller the aperture (i.e., f) number the more shallow the depth of field will usually become.
I made the image directly above by critically focusing on the eyes of my primary subject, a lovely lady in Beijing, and employing an aperture of f/4 to place emphasis on her by rendering the other dancers surrounding her out of focus.
Conversely, a physically narrow aperture, such as f/11 or f/22, will generally produce a large depth of field.
The image directly above of three Aussie tourists at the Perry Sandhills, near the town of Wentworth in rural Australia, is a great example of a large depth of field.
I made the photo at an aperture of f/11 which allowed me to render all of the image, from the immediate foreground all the way to the distant background, nice and sharp.
The Concept of Focus in Photography
Think of focus as a measure of distance.
The sharpest part of an image, assuming either the subject or the camera doesn’t move during the exposure, will always be the exact distance, in meters or feet, at which your lens is focused.
I’d define depth of field as an impression of sharpness, both in front and behind the actual point (e.g., subject) at which the lens has been focused.
Lens Focal Length And Its Impact On Depth Of Field
A wide-angle lens (e.g., 18 mm) will produce a larger depth of field than a more powerful focal length (e.g., 55 mm) would at the same aperture and camera to subject distance.
The photo immediately above of moss covered trees in the beautiful area known as Paradise near Queenstown in New Zealand was made at a focal length of 24 mm at an aperture of f/16 on a Nikon D800e full frame camera.
As well as the wide angle of view produced by the 24 mm focal length the depth of field in this image is huge, extending from the near foreground through to the background.
Conversely, the close up image of a King penguin's feet on Cuverville Island in Antarctica was made on a full frame Canon 5D Mark II camera with a Canon EF 100-400 mm lens at a focal length of 400 mm and an aperture of f/5.6
The depth of field in this image is incredibly shallow as evidenced by the penguin's left foot being sharp while almost everything else in the image, including its right foot, has been rendered out of focus.
That’s the kind of depth of field you can expect when working with a powerful telephoto lens at a relatively wide aperture.
How Camera To Subject Distance Changes Depth Of Field
The closer you get to your subject the more quickly the surroundings, by which I mean the foreground and background, will fall out of focus.
Conversely, moving further away from your subject and then refocusing your lens will increase the depth of field.
Both the image above of the dandelion and the one below of surf and mist rolling onto Inlet Beach at the tiny tourist town of Aireys Inlet, along Australia’s Great Ocean Road, were made with the same lens.
While the aperture is somewhat different, the main difference is in the camera to subject distance and how that effects depth of field.
I think you'll agree that this comparison shows just how significant a change can be achieved with a radically different camera to subject distance.
Fast Lens and Shallow Depth Of Field
One of the problems folks have achieving a shallow depth of field is due to the fact that the lens they use (probably a kit lens) does not have a particularly wide maximum aperture.
While f/3.5 is relatively wide, apertures of f/2.8, f/2 or f/1.4 will produce images with significantly shallower depth of field with the same camera, lens focal length and at the same camera-to-subject distance.
Furthermore, the maximum aperture associated with most kit lenses varies with the focal length. As you zoom in, to bring the subject or scene closer, you loose the ability to gather light.
As a result the lens's maximum aperture is reduced from, for example, f/3.5 to f/5.6.
While zooming in should, in theory, create a more shallow depth of field the resulting reduction in maximum aperture, from f/3.5 to f/5.6, may well prevent that from occurring.
So, while kit lenses are affordable, they involve compromise.
If you’re working with a kit lens and are looking to produce a very shallow depth of field it’s probably best just making your photo at a distance that’s closer to your subject than you otherwise would have.
It's a great solution which, to all intensive purposes, appears non-technical. And that's the beauty in it, wouldn't you agree?
Do you live in or around Melbourne, Australia and are interested in learning more about how to use your camera to make really great photos?
Be sure to click the image above for details on a special one-to-one, private Melbourne photography class with me.