Inspiration, Pro Tips

Deep Focus and the (Relatively) Lost Art of the Split Field Diopter


Great filmmakers are effective manipulators, and they use many visual and audio tricks to create moods, feelings, and meaning. Whether it’s with their lens choice, their camera angle, or the way they work with their actors or subjects, each plays a part in the overall experience. One of these tricks is called “deep focus,” and it can be used to literally (and figuratively) add layers to your composition, expand visual information in a scene, and juxtapose different subjects that have a relationship.

Typically, the majority of the focal planes in films and videos are shallow, and our eyes are automatically directed to whatever is in focus as the thing that we need to look at. With deep focus, however, everything in the frame is in focus, allowing our attention to be put toward looking at the overall picture, and how everything is related within the frame. The ideas of mise-en-scène and having everything in its place are important to an effective use of deep focus, because it can force you to creatively think about compositional details to make a more detailed and interesting scene.

Deep focus can be created practically within the camera or with a filter, but it can also be created with compositing. Doing it practically requires more precise work and thought up front, while the latter requires more work in post and an additional shot, usually with a different focal plane. First, let’s talk about the practical ways.

In Camera, No Filter

The goal is to have everything in the frame as sharp as possible. Using a wide-angle lens, shooting with a small aperture, and having lots of light are the crucial big steps (it’s also easier to shoot deep focus if the camera has a smaller sensor) for this. Once you have these figured out, it’s as simple as staging your scene and taking full advantage of the space in your frame. Fill it with layers of information to tell a detailed story, or leave it all empty and show the vastness of the setting. Either way, the deep focus keeps it all important to the shot.


Using the Split Focus/Field Diopter

The split focus/field diopter is a piece of convex glass that covers only half of the lens, making the half it covers near-sighted. This means a background object will be in focus, and a foreground object that’s positioned in front of the filter will also be in focus, giving the illusion of deep focus. The area between the objects will be blurred or distorted, which you’ll notice in the examples below, but directors have used pillars, walls, or other objects to creatively hide this “defocused” line.

Hand Reaching Around a Corner to Flick Switches by davidkrug

You can experiment with juxtaposing different subjects together in the same frame, but at different distances from the camera, all while keeping them in focus. Alfred Hitchcock, Steven Spielberg, Quentin Tarantino, David Fincher, Brian De Palma, John Carpenter, Alfonso Cuarón, and nearly every director in the 70s and 80s used a split field diopter for deep focus in their films. Star Trek: The Motion Picture, Citizen Kane, and Blow Out are some of the most often-cited. Here’s a supercut of some notable examples:

It’s not as popular as it once was, but the filter can be used to show a ton of information and create an unnatural feeling, since our eyes don’t usually see things this way. Viewers can also get a closer look at a foreground object or a subject’s facial expression that they otherwise wouldn’t be able to get with a normal shot. This filter is not necessary for achieving deep focus, but there’s something special about the look that it creates and the feeling(s) it conveys. A director can create specific and detailed movements and positions for everything in the frame, painting a rich tapestry of visual information that tells as much of the story as the dialogue does, if not more.

The filter is usually either mounted in front of the lens or directly onto the lens itself, and can run anywhere from $15 to several hundred dollars.

As great as the split field diopter can be, it can also be limiting. Shooting with a practical filter in-camera can reduce flexibility if you want other options. It’s also a lot of work up front, and perhaps most obviously, it can be replicated in post-production rather easily.

Compositing for Deep Focus

Thanks to the cost and ease of digital filmmaking, shots don’t need to be staged as strictly to pull off the deep-focus effect. You can simply set up two different but identically framed shots with different focal planes, then stitch them together or mask them in/out in editing (you still want to keep a relatively deep focus so they match as much as possible).

The biggest downside is that you have to make adjustments to the camera, making sure not to move anything in the frame, and then re-shoot the second take to get it to match seamlessly. Walls and other stationary objects or lines in the frame are important to use for covering up the “seams,” just like you would with a filter.

Take a look at this well-known diopter shot from Pulp Fiction. Observe the wall’s edge and notice the slight “fuzziness”:

If you were to composite these two together, however, you would use that same wall edge for your mask. You’d then shoot one side of the frame, then the other, adjusting the focus for each shot. It’s hard to say which one would be more work, but either one requires planning ahead of time to pull it off.

The beauty of the deep focus shot is that it’s another way to be creative when you’re shooting. Whether or not you use a filter is up to you, your budget, and time. Using deep focus can also force you to be more thoughtful with your compositions, because a well-executed shot can be remembered for a long time. In the end, adding another shot to your repertoire is always a good thing.

What do you think? What are some of your favorite split-focus shots? Tell us in the comments!

Top image: Still from O Brother, Where Art Thou?, courtesy of Buena Vista Pictures