Focus, Blur, and Depth of Field
Everything you need to know about sharp pictures, background blur, and the hyperfocal distance.
If you have ever been to a movie, or looked at a good portrait, you might have noticed how blurrry the background often is. This effect is called the depth of field – and it’s really easy to achieve! Read on for a short primer on all things depth of field – or DoF, as it‘s often shortened.
So, how do we get that blurry background? It‘s all down to the lens. When you take a shot with your camera, there actually is only one single distance from your camera at which objects appear sharp. This distance is called the focus distance, and it‘s just the distance that your lens is focused to. Every object that is closer to your camera, or farther away, is (at least) a tiny bit blurry. Objects that are close to the focus distance are still mostly sharp, while objects that are further away can be almost invisible due to the blur.
Image Credit: Human Outline by Holek on Wikipedia
The area in your shot that‘s still sharp enough is called the Depth of Field, or DoF. The Depth of Field can be shallow (ie, only a small range of distances is in focus) or wide (when almost every object is in focus).
With a shallow depth of field, objects that are further away than your subject appear blurry – like the background in this macro shot. A shallow depth of field allows you to separate your subject (e.g., a face in a portrait) from your background, and creates a beautiful bokeh (the blurry background often seen in the cinema). This is most often used in macro images or portraits, but it can be a powerful tool in almost any setting.
With a large or deep depth of field, most objects is sharp and in focus. his is great not only for landscape and architecture settings, but for many other scenes as well.
You can easily get both of these effects! Here are some easy tips.
How do I get a shallow Depth of Field?
Let‘s look at four different photos with a shallow depth of field, and see how you can achieve this effect.
Macro, Portrait (55mm, 5.6, weit weg), Stadtszene (f1.4) (Stock), Vogel-/Tierbild
To achieve a shallow Depth of Field, often called the „cinema effect“, use
- a large aperture (a small f-stop, like f/1.4)
- a tele lens with a long focal length (like 70mm)
- a camera with a large sensor (e.g., a full-frame-camera)
- a small distance from your camera to the subject, and a large distance between your subject and the background. (Explainer image)
You don’t need to use all of these suggestions! It‘s absolutely possible to achieve a beautiful portrait shot with stunning bokeh with a standard 18-55mm @ f5.6 kit lens on a small camera. In this case, #4 becomes really important! Make sure to get as close as possible to your subject, and to use a background that‘s relatively far away. Trees, sunsets, or city scenes from a riverside work well for this.
How do I get a wide Depth of Field?
Alright, so we know how we can geht that beautiful, dreamy background. But what about perfectly sharp architecture shots? What about landscape photography? Crisp late-night city shots? Let‘s take a look at a few situations with a wide DoF, and see how we got there:
Landscape, architecture (hohes f), Handy-Bild, macro (focus stacking)
To create photos with a wide / large depth of field, use
- large f-stops (like f/11 – but beware!)
- short, wide-angle lenses with small focal lengths (e.g., 17mm)
- a camera with a small sensor, or your phone
- a large distance to your focus subject
- focus stacking.
Again: you do not need every one of these (especially not focus stacking) for your photos to be crisp. A wide Depth of Field is often easier than a shallow Depth of Field.
Bringing it all together – Optimal settings for your Situation
By now, you hopefully have some intuition on how you can get blurry backgrounds or the cinema effect, or tack-sharp images. But these are the extremes. In most of your photos, you actually want to balance your depth of field to create the best photo. And even if you‘re after maximum background blur, you should not forget that you want your subject (wether that‘s your girl- or boyfriend, your dog, a house, or a flower) to be sharp and in focus.
Of course, there‘s a solution to this problem. In the old times (TM), people used to carry around small tables that listed the length of the depth of field for different apertures, focus distances, and focal lengths. Thankfully, we are in the age of the smartphones, and depth-of-field calculator apps. My app, light&depth, contains a beautiful and easy to use Depth-Field-Calculator, that you cantry out for free on your iPhone. (It will also support your camera. I promise!)
light&depth is different from other DoF calculators in that it will actually incorporate the resolution of your camera into its application, if you choose to do so. (RW!)
Screenshots
It can help you in two ways:
First, you can calculate the Depth of Field for every situation. Simply enter your camera, the focal length of your lens, and your aperture, and light&depth will immediately show you how large your depth of field is, where it begins and ends, and a lot of other useful information (including the hyperfocal distance!). It‘s designed to be a great tool to build intuition and to learn from. You can change values quickly and directly see their effects – no „calculate“ button needed. That way, you will quickly know by heart which apertures, focal lengths, and distances create exactly the effect you want.
You can also use the „inverse mode“, which is really useful to get the depth of field just right. Simply enter two points that should be sharp, and light&depth will calculate optimal settings (including diffraction) that lead to a perfectly sharp image.
light&depth is great for learning, but it‘s also a really powerful tool. It includes diffraction, which can lead to blurry pictures at high f-stops. You can use multiple cameras and quickly change between them, add presets for often-used situations, and even adjust the visuals!
Now, get out and explore!
So – How do I get this?
The Depth of Field (often shortened DoF) of a photo depends on the aperture (f-stop) you use, your camera, and your focal length (how zoomed-in your photo is). Simply put:
- A large aperture (that means a small f-number, like f/1.4) will create a shallower depth of field than a larger aperture (like f/16).
- A larger camera sensor (like that of a full-frame camera) leads to a shallow depth of field; smaller sensors (like those in your phone) often have a very deep depth of field.
- The longer your focal length (the more you zoom in), the shallower your depth of field will become. Wide-Angle shots at smaller focal lengths often have a large or infinite depth of field.