Depth of Field in Your Video: Why and How to Use It
Published on December 8, 2016
Depth of field is a very technical-sounding term, but don’t let that scare you off. It’s simple to understand. If you use it well, you can transform ordinary images into cinematic marvels that your friends, family, and clients (and you!) will love.
Today I’m going to share with you what depth of field is, why you might use it, how to create it, and also throw in several helpful tips that will make it easier to work with.
First, what is it?
What is depth of field?
I prefer to avoid highly technical mumbo jumbo, so I’ll say it like this:
It’s the area of your image that’s in focus. In other words, you can use it to make blurry backgrounds and blurry foregrounds.
And we all know that blurry backgrounds look awesome.
You’re shooting video of your daughter about to blow out the candles on her birthday cake. The camera is at her eye level from directly in front, and we’re pretty close on her face. Your daughter smiles as we hear other children singing happy birthday in the background. The lit candles are between us and her face, and because we’re controlling depth of field, they’re out of focus. They’re just blurry, glowing circles.
Then at the last moment, right as she inhales and blows out the candles, you quickly adjust the focus so the candles are sharp, and your daughter’s face is blurry.
That’s some good video right there!
When you do this, you’re applying the concepts of cinematography to your video. Do you see how it can add visual interest?
(Of course, you might need to practice the focus-change a few times before the actual attempt. You wouldn’t want to keep re-lighting the candles to practice again. The other kids might get a little impatient. This is all…ahem…hypothetical.)
Why Use Depth of Field?Here are some of the reasons I love using a shallow depth of field:
- It directs the viewer’s attention. When we strategically place things out of focus, the viewer doesn’t pay attention to them. Viewers focus on the part of the image that’s in focus.
- It reduces distraction in the background. Distracting backgrounds can be a huge problem. And unfortunately, they tend to be a normal part of video. You can control depth of field and make distracting backgrounds bearable.
- It makes the image look more cinematic. If you’re going to be shooting video anyway, you might as well make it look cinematic. :)
- You can add visual interest. In the birthday cake example above, I described a technique called a “rack focus” which is simply shifting the focus from something in the background to something in the foreground, or the opposite direction. This a technique you can do in video, that you can’t do in a single still photograph.
You can probably think of more reasons, but these are the big ones I could immediately generate.
So now you know why to use depth of field. Now the question is…how?
A Shallow Depth of Field: How to Create It
Would you be surprised to find out that your current video camera can most likely create a shallow depth of field?
There are a few exceptions, such as the small pocket cameras like the Flip Video camera, Kodak Zi8, or the iPhone.
However, with a traditional video camera, here’s how you create a beautiful shallow depth of field:
- Move far away from your subject (because you’re going to zoom in a lot.)
- Zoom in a lot (maybe all the way).
- Open the aperture on your camera all the way. This might be called the f-stop or Iris on your camera, but open it all the way up. It could be that your video camera has a mode called “portrait”. If so, choose that mode.
What you’re going for here is a long focal length (which is why you move away from the subject and then zoom in) and a wide open aperture (lowest f-stop number).
Most video cameras have small sensors, so it’s hard to get a shallow depth of field. But you can do it with the above steps.
If you’re shooting video with a digital SLR camera or one of the new large single sensor video cameras (such as the Panasonic AG-AF100), then you’ll find it much easier to create a shallow depth of field.
The bigger the sensor, the easier it is to create a shallow depth of field. This is why the Canon 5D Mark II with its enormous sensor is great for this.
Generally speaking, with more traditional video cameras you have to move away further and zoom in, whereas with the cine style cameras with the big sensors, you don’t have to move so far away. A nice focal length and a big sensor make it easy for you to have a shallow depth of field.
Depth of Field TipsThese additional tips will come in handy…
The Neutral Density Filter Is Your Friend These are filters you put over your lens that reduce the amount of light going into your video camera. Some higher end video cameras have neutral density filters built in. Others you’ll need to manually attach to your video camera. When you’re shooting video outside in the sun and you open the aperture all the way, your image will overexpose unless you increase the shutter speed. But you might not want to increase shutter speed because it will create unnatural motion blur. What do you do? Put a neutral density filter on the lens to knock the light level down a couple stops.
Difficult to Focus One of the problems with shooting video with a shallow depth of field is that it’s hard to keep important things in focus, especially if they’re moving.
Some tips that might help with the focus problem:
- Maybe don’t open the aperture ALL the way up. Consider shooting with F4 or F5.6 and see if you like the look. If you’re shooting video of a person’s face, and one of their eyes is in focus while their other eye is a little out of focus, well it might be time to close the aperture a little. As you close it down, you get a deeper depth of field which means that more area is in focus. This tip is a good one for cameras with very large sensors, such as the Canon 5D Mark II.
- Use an external monitor (preferably a large one), instead of trusting the video camera’s built-in screen. When you’re shooting with a shallow depth of field, it’s totally possible that you *think* your subject is in focus but then when you go home and see it on the big screen, it turns out that the focus is soft. The little LCD screen on the camera is usually not a great way to judge focus. You need a big screen to reference. A good external monitor will have size, and maybe other features such as peaking (solid colored lines that the monitor draws around sharp edges), or other focus assist features.
- You’ll need a tripod for shallow depth-of-field work. Shakycam can look good with a wide angle lens, but with a long lens and shallow focus, shake doesn’t look very good. I highly recommend using a good fluid head tripod to stabilize your camera.
- You might need someone else to handle the focus. In fact, there’s a title for this job. It’s called a focus puller. If you’re shooting a cine style project with a shallow depth of field, it can be a complete job just to keep the subjects in focus within the image. Hence, the focus puller.
Depth of Field: Achieving the Film LookSure there are other things that create "the film look” with video — think lighting, color, and composition — but if you control the depth of field, you’ll find that your moving images will instantly look more like film.
Ready to make your videos more cinematic? Take control of depth of field, and you can do wonders.
Two additional quick things:
- If you want to read up on all the technical mumbo jumbo on depth of field, check out this Wikipedia entry.
- Almost five years ago I created an introductory video about depth of field. I’ll embed it below…
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