Understanding Depth of Field
What is ‘depth of field’? It’s simple. At its most basic, It’s how much of your scene is in focus. That’s it.
And here’s a more complicated definition. Depth of Field is the distance between the closest objects in focus and the farthest point of focus.
Consider this. You are out photographing a beautiful landscape. And you want to be able to see the whole scene for what it is.
Here, you would use a deep depth of field, as it will keep your foreground and background in focus.
Now, you are walking around a city, trying to capture portraits of people. You want to cut out the distracting background, so you use a shallow depth of field in your photography.
Here, your foreground is in focus but the background is not.
Your aperture or ‘f/stop‘ is what indicates your depth of field. If you don’t know about aperture, then you need to read this post first.
The wider the aperture, the shallower the depth of field and vice versa. The diagram below explains this.
Is Depth of Field Equally Distributed in Front and Back of my Focus Point?
When you place your focal point on a subject, there is a depth of field range. This means that before and after that focal point is a distance where everything in focus. The larger the narrower the aperture, the larger the distance.
But, is the distance before and after the focal point the same? You would have thought it was, but it isn’t. Usually, one-third of your focus falls before the focal point, and the other two-thirds behind.
As your focal length increases, it becomes more equal. Let’s look at an example using two different lenses. The Canon EF 50 mm f/1.2 L and the Canon EF 200 mm f/2.8L.
How Does the Focal Length of a Lens Control Depth of Field?
The focal length of the lens is how close you can photograph a subject. A wide focal length lens, such as 14 mm will give you a field of view of 114°. A telephoto lens with a 200 mm focal length gives you a 12°.
Without becoming too over complicated, a longer focal length will give you a shallower depth of field. Let’s look at an example:
Images that show selective focus have a shallow depth of field. This means that the range of focus is very small. Let’s look at an example using two different lenses. The Canon EF 50mm f/1.2 L and the Canon EF 200 mm f/2.8L.
Let’s say your subject was 10 meters from the camera. By using a focal length of 50 mm at f/4, your DoF would be 6.77 – 19.1 m. Everything between these distances (12.4 m) will be in sharp focus.
Does Distance Affect Depth of Field Photography?
Yes it does. Your Depth of Field photography also changes with distance. While photographing a close subject, your depth of field is smaller or narrower.
Moving farther away from a subject will make your depth of field photography wider. Moving closer to your subject will make it shallower.
The background and the foreground effectively become closer. This is when compared to the distance between you and the subject.
There is one instance where your depth of field can be manipulated. That is by using a tilt and shift lens. By playing around with the ’tilt’ of a lens, you can place an entire scene in focus when using a wide aperture.
Shallow Depth of Field Photography
A shallow depth of field comes from using a large aperture. Anything between f/1.4 and f/4 will give you a shallow depth of field photography.
This is a great way to separate your foreground from its background. The background might be uninteresting, distracting attention from your subject.
You can even use depth of field photography to single out a point of interest. This is especially helpful in an otherwise busy scene.