Learn to control depth of field and unlock more of your creative photographic potential
You’d think photography was all about recording things in sharp focus, but that’s only part of the story. A very satisfying technique for creating great photographs is to balance what’s in focus with areas that are very much out of focus. We’re talking DOF or Depth of Field.
What is Depth of Field?
Technically Depth of Field, which we’ll refer to as DOF from now on, is the range in front of and behind the subject you are focused on that is in sharp focus. For some types of photograph, like macro photography and landscapes, for example, the goal is usually to get as much of the scene in focus as possible. But by limiting DOF you can creatively isolate the subject from the surroundings.
This usually results in an attractively blurred background. This is often referred to as bokeh. Sometimes blurring the foregroud in front of the subject can add to overall result.
In this gallery you can find some examples of the use of limited DOF:
How do you limit DOF?
The DOF you see in an image is proportional to several factors. Fundamentally, the smaller the physical aperture size inside the lens is, the greater the sharply focused range in your your image. Cameras with very small frames or sensors tend to have small apertures.
Smartphones, for example, have little space to house a camera so the lens must be very small. This means a small sensor and so a small aperture. The ultimate depth of field camera is a pinhole camera. A smartphone’s camera is close to being a pinhole camera, which is why it’s difficult to limit DOF with camera phones.
Another factor is the lens focal length. The longer the focal length of the lens, or the more it tends to be a telephoto lens, the less DOF will be achieved. To demonstrate this, it’s very difficult to get the characteristic limited DOF blur with a wide angle lens than it is with a telephoto lens.
So the magic formula for getting limited DOF blur is to have a camera with a reasonably large sensor, with a lens that isn’t too short in focal length and which is set to a wide enough aperture.
Here is a photo taken with a medium telephoto lens at an aperture of f/2.8. Th background is blurred, isolating the foreground leaves nicely.
If you are having trouble getting the background to blur adequately, try stepping back from your subject and zooming in on your subject so that they fill the same area of the frame.
Sometimes, if you are very unlucky, you might be saddled with a lens that is inherently poor at being able to blur background details attractively. The result is known as ‘busy’ bokeh and is caused by the optical design of the lens.
Blurring is sometimes not enough
Even if you can get background blurred some care is required to ensure that some unwanted features of the background spoil that precious bokeh. Below is an example where some distracting bright colours have survived the action of being blurred:
If you would like to explore the detailed technicalities of DOF I can recommend the DOFMaster website. The mathematics of the optics behind DOF are explained and you can use their online calculator to estimate DOF based on the type of camera you have, the lens settings and the distance you are from the subject.
Finally, if you have any questions about DOF and how to get to grips with it, or if you’d like to show us your limited DOF images, you’re welcome to post a comment further down this page.