Making blurry, beautiful backgrounds is one of the top questions new photographers want to find the answer to.
The answer to this question is simple: create shallow depth of field.
The way to do this, however, is commonly misunderstood.
When you first learn about exposure, you learn about the aperture – the size of the opening that lets light in.
Aperture has a direct influence on depth of field.
Large apertures like f/1.8 let lots of light in and create a shallow depth of field. Small apertures like f/16 let less light in and create more expansive depth of field.
So it makes sense to use a large aperture to create shallow depth of field, right?
Here’s where the misconception occurs.
While aperture does influence depth of field, it’s just one part to the story.
You don’t need a fancy, expensive lens with a super large f/1.2 aperture to create blurry backgrounds. Nor do you need a thousand dollar telephoto lens.
Instead, all you have to do is have a better understanding of the three factors that influence depth of field.
Factor 1: Aperture Opening
The fact is that a large aperture does create a more shallow depth of field.
Use an f/1.8 and you’ll find that lots of blur is added to background elements compared to using a f/8 or f/11.
In the example below, you can clearly see the background with an f/16 while an f/4 blurs it significantly more. The focal length remains the same for all three images.
This happens because of focus area.
When you focus a picture, you have to select one single spot. This is then becomes the sharpest area of the image.
This all happens on the depth,or z-axis.
Think of the z-axis as an imaginary line going from your camera lens directly out into the horizon.
Where you set your focus point and say ‘this is going to be the sharpest area’, this is just one point on this z-axis.
Your camera then makes that point as sharp as it is capable of. Of course, sharpness doesn’t just start and end at that point. It continues in front of and behind that spot as well.
How much in front of and behind that point sharpness continues is determined by your aperture size.
The larger the aperture, the smaller the area of focus around this point.
Aperture opening, however, is only one factor that affects depth of field.
Factor 2: Subject to Background Distance
Take a look at the example below. Both images were shot with the same aperture opening. The only difference is the distance of the subject from the background.
In the first image, the subject and background are close together. The background isn’t very blurry. In the second, subject and background are far apart. The background is more blurry.
Increasing the distance of the subject from the background pushes the background outside of the range of the focal area, as we saw from the illustration earlier.
To better understand this, let’s revisit that Z-axis.
You have your subject which is a certain distance from your camera on the z-axis. This subject is where you also place your focus point. It’s the sharpest point.
Now let’s say your background is right next to your subject. Being so close together, even the largest aperture leaves both subject and background within the focus area of the z-axis.
Move them farther away from each other on the z-axis and the subject will remain in the focus area while the background becomes outside of the area.
In the example illustrated here, the Z-axis is a diagonal line. It follows our normal view of the world – with a normal focal length.
Note that you still have to move the subject quite a bit away from the background to create background blur.
Change the z-axis angle and you’ll affect depth even more.
Factor 3: Focal Length
All of these examples and diagrams we have looked at had a static z-axis.
This is not the case in the real world.
You can make the z-axis less steep or more steep. You do this with focal length.
A wide angle lens creates a very large angle on the z-axis. This consequently means that we have to do a whole lot more moving of subject from background to get blur.
The reason is that this large angle makes everything appear so far apart, when they’re actually pretty close and all within the same focus area.
This is why wide angle lenses are typically avoided when you’re going for a strong background blur.
The more you zoom in (or increase your focal length), the steeper this z-axis angle becomes.
This compresses distance allowing you to have a subject and background within the same frame even though they’re miles apart.
Cameras aren’t made to keep these distant areas both in focus at the same time. Even the smallest aperture doesn’t have a focus area that large.
The end result is background blur or shallow depth of field.
Take a look at the example below. You can see much more clarity in the background with the smaller focal length than with the longer 100 mm one.
Distance Adds Depth
Shallow depth of field is made when you have more distance between subject and background.
You don’t need a fancy f/1.2 aperture lens to create extremely shallow depth (although it’s definitely nice to have).
All you have to do is two things:
- Move your subject far away from your background
- Move your camera far away from your subject
- Zoom in to your subject (or use a telephoto lens), optically compressing distance
While telephoto lenses compress distance, the distance is still there. The end result is shallow depth of field.
Remember, depth of field relates to the focus area on the z-axis. There are three factors that what ends up in this focus area and is rendered sharp, and what’s left out of the area and made blurry.
- Subject to background distance
- Focal length