Depth of Field(DOF) vs Bokeh
17 JAN, 2020 | BY YU CHENHAO
Depth of field, one of the most important tools for a photographer which helps the photographers in photographing the aesthetics of the subject and the background. In portrait photography, many of you know one principle that distractions should be removed from the background to extrude the subject, so you can adjust apertures, focal distances or lens, in order to create a blur background or foreground, or just call it: Bokeh.
As a result, however, in many photographers opinions that bokeh is simply equated with a shallow depth of field or just a lower f-number when they master the basic options of a camera. They spend lots of time take the depth of field into practice without completely understanding even its definition nor knowing how to properly use it. So they often confuse DOF and Bokeh, and can not properly create portrait effect.
Bokeh and shallow depth of field are absolutely not the same. But before we compare the both sides, let’s figure out the definitions first.
1. What is Depth of Field?
To achieve a striking effect that we want when we shoot portraits, we choose MF mode (manual focus) to better control the sharp or blur parts in the frame. That’s because a digital SLR camera can only focus at one distance at a time, sharpness gradually decreases on the parts which are out of focus. So we can regard the depth of field as the area of sharp focus.
According to Wikipedia, “ depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. “ For a particular focal length, the nearer you focus the more distributed your DoF will be. In portraits, it means the closer to your subject, the shallower the depth of field, which will profoundly be separating your subject from a properly blurring background or foreground.
2.Depth of Field vs Bokeh
In photography, bokeh is always used to describe the quality of the blur produced in the out of focus areas in an image produced by a lens. So, comparing with the shallow depth of field, which is regarded as the area of sharp focus, bokeh is the quality of the background and foreground blur.
You can achieve a shallow depth of field by decreasing the camera-to-subject distance (move closer to your subject), or choose a lens with long focal lengths and set a wide aperture. But these operations do not always mean a nice bokeh. The bokeh, on the other hand, is influenced by the phenomena outside the focal plane like foreground/background brightness, lens aberration, shutter speed, color and shapes & patterns of the subject, etc.
For example，you can achieve a wide-angle with a deep depth of field and a nice bokeh at the same time with a Canon 24-70mm f/2.8 lens, but you may fail to get a nice bokeh with a Nikon 18-105mm f/3.5-5.6 even when you have a shallow depth of field.
With the explanations above, now here are some suggestions for you to get a nice bokeh, in order to create a perfect background for your portraits:
- Choose a long focal length like 50 mm or more to get shallow depth of field.
- Select a wide aperture (f/1.4, f/1.8, f/2.8).
- Get close to the subject.
- Focus your lens on the area you want it to be crisp and sharp.
- Put your subject far from the background that you want blurred out.
Also, if there is enough budget, you can choose a lens that has more aperture blades with curved edges to make the aperture more closely approximate a circle rather than a polygon. The blades define the shape and size of your bokeh. The wider the aperture the wider your bokeh, and more blades will help.