Differential Focus and Selective Focus are the same thing
Differential focus is a photographic composition technique involving, believe it or not, focus. It is also referred to as selective focus. The photographer deliberately chooses to have part of the image in sharp focus while allowing other aspects of the image to be out of focus.
Our eyes naturally seek sharp focus, so when we view an image we glance over the out of focus areas seeking the sharply focused areas. By using differential focus we are directing a viewer’s eyes to the area we want to emphasise. The out of focus area, however, still forms an important part of the story or atmosphere of the image.
Choosing your focus
Because the sharpest part of the image is where your viewers’ eyes will ultimately rest, you need to decide what is the most important part of the image. What are you saying with the image?
An ideal example of this is a bride and groom next to their wedding car, with the focus on the ribbon and bow details. Obviously it is a wedding and the most important aspect of any wedding is the bride and groom. However, choosing to focus on details, with the bride and groom out of focus in the background, tells the story of their day and highlight the details that they specifically chose to celebrate their wedding day.
Here two composition techniques are being used: framing and differential focus. Settings: focal length – 62mm, aperture – f5.6.
Deciding on focus
When deciding to use differential focus, you also need to consider how blurred your out of focus areas need to be. If the background is too blurred, it is not contributing to the story, but rather simply acting as a means to making the subject stand out.
So, how little focus is too little?
Deciding on how out of focus your subjects again highlights the open-ended decision making in all things related to photography. There is a broadly acceptable range of blur and it depends entirely on the photographer as to how far to push the limits before going too far.
A good rule of thumb is that if you can’t instantly figure out the objects in the out of focus areas, you’ve gone too far. Your viewers’ eyes won’t take it in at all and your message will be lost.
Out of focus people
Bear in mind when you have blurred people in the background of your photos, that they should not be looking at the camera. This is simply because our eyes are naturally drawn to another person’s eyes.
If somebody in the blurred background is looking to the camera, their gaze will tug a little too hard on your viewers’ attention.
Camera settings: focal length – 70mm, aperture – f8.
How to achieve differential focus
There are a few ways to create differential focus in your photographs.
- Narrow depth of field
- Using a lens with a long focal length
- Distance between subjects within an image
- Camera sensor size
To understand the role of each of these three factors, read our tutorial – Using depth of field for gorgeous photography composition
To further refine your skills when using aperture to create a narrow depth of field, read The Exposure Triangle – what role does Aperture play?
How to actually focus
Of course, the most important aspect of differential focus, is the actual focus. So, let look at auto focus modes and auto focus area settings on your camera.
To successfully and consistently apply differential focus to the part of the image you want sharply focused, you need to know how to use the auto focus settings on your camera.
Auto focus modes
Choose between 2 auto focus modes:
Continuous Servo AF (Nikon), also called AI Servo AF (Canon) – your camera will continuously focus (like the name suggests) while you partly hold down the shutter button, or fully depress the back button focus.
Single Servo AF (Nikon), also called One-Shot AF (Canon) – again, as the name suggests, when you depress the shutter button to focus, your camera will focus and lock on that focus until you fully depress the shutter button to take the photo, or release the button. This is true also when using back button focusing.
Choose your auto focus area:
The only auto focus area you should be using when shooting with differential focus is single point auto focus. With this method you decide on where the focus will be and place your focal point on that area.
You can’t leave it to the camera to decide on what you want in focus. It may be a super awesome, top of the range DSLR camera, but they haven’t yet included mind reading technology with DSLRs.
Who knows, maybe in the future you’ll just have to think of an image you want to create and the camera will magically do everything. For now, learn to use single point focusing.
Further reading on focus:
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