Woman with soft focus “bokeh” lights in background

As your grasp of videography grows,  you’ll start to understand how you can control emotion and design through the use of depth of field. This article talks about what determines bokeh and what makes one type more pleasing than another.

I once showed a veteran cameraman a shot I was particularly proud of. He looked at it briefly, grunted and said “that’s some mighty funky bokeh you got going on there.” And went back to whatever he was doing. Funky bokeh? I was really puzzled. What was he noticing in my shot that I wasn’t? And what was that word, “bokeh”? It sounds like a Sunday morning cartoon.

What the Heck is Bokeh?

It’s inevitable that the more you learn about a topic the more detail you see in things. Searching the Internet you might learn that “bokeh” is a Japanese word for describing the out of focus areas in an image which has no English equivalent, but that’s actually wrong. It’s sort of like saying “Godzilla” is a Japanese word describing a giant city-smashing monster that has no English equivalent. The english word for “bokeh” is “bokeh” and among videographers, photographers and cinematographers, it’s commonly used.

Bokeh doesn’t describe how out of focus the background is, only how nice it looks. Depending on the design of a lens the out of focus areas can be pleasing or … “funky.” In this article we’re going to take a look at the things that make up pleasing bokeh which will help you in your future choices of lenses so that when you show your meticulously shot scene to a crusty old cinematographer, he’ll say “that’s some mighty fancy bokeh you got going on there.”

Bokeh and Depth of Field – Inescapably Entwined

Out of focus areas, without in focus areas, are just out of focus. Any talk about bokeh really needs to begin with a discussion of depth of field: the area of a shot which is in focus. “Depth of focus” might be a better term for it.

Depth of field is usually defined in terms of “shallow” or “deep.” A shallow depth of field has a very short distance from the lens, sometimes a fraction of an inch, where objects are in focus. A deep depth of field may extend from a few inches to infinity.

Bokeh doesn’t describe how out of focus the background is, only how nice it looks.

There are two factors that determine the depth of field: the aperture size, and the distance from the lens to the subject. The closer the object is to the lens, and the wider the aperture, the shallower the depth of field. There are two other things that don’t actually affect the depth of field, but they seem to. (What!? Don’t fret, it’s not really that confusing.)

Bokeh doesn’t describe how out of focus the background is, only how nice it looks.

Focal Length

First: the focal length of the lens does not actually affect the depth of field. The focal length does, however, affect how magnified the out of focus areas are in your frame, and it affects how far your subject needs to be away from your lens, so the magnification of the lens makes it appear that the background is more out of focus by giving it more screen space. If this doesn’t make sense you can safely pretend that the longer the focal length the shallower the depth of field, just remember it only looks that way and don’t say it at parties where there are fancy cinematographers.

Sensor Size

Second: the size of your sensor doesn’t affect the depth of field, but again, like focal length, since it affects what you can fit on your screen, it influences your choice of focal lengths which affects the appearance of the depth of field.

Until recently, shallow depth of field was relegated to big motion pictures. Consumer and prosumer video cameras without interchangeable lenses didn’t have the apertures necessary for very shallow depth of field and for that reason, shallow depth of field is something that’s associated with high budget movies. However, at the same time, movie makers were trying to figure out how to get really long depth of field, in some cases inventing things like the split-focus diopter that focused differently on different sides of the frame, or even compositing two images together to get someone in focus in the foreground and someone else in focus in the background.

A split-focus diopter was used in Robert Wise’ 1979 Star Trek: The Motion Picture to keep Persus Kambatta in focus on the left and William Shatner and Leonard Nimoy in focus on the right. In between the two, you will notice an inexplicable out-of-focus area; that’s the space in between the two halves of the diopter not actually focused on anything. Most movie viewers don’t notice such shenanigans, but now you will, every time you see it done.

With more and more videography being done with DSLRs, very fast, inexpensive interchangeable fixed focal length lenses, with their shallow depth of field, are now easily within the reach of prosumer videographers. Want some captivating video? Try putting your subject close to the camera, adding a simple 50mm lens, opening up the f-stop to f1.8 and watch your subject pop out of the background. Be careful however, the very narrow depth of field makes it easy to have your subject out of focus if you’re not paying attention.

Now, What’s with the Funky Bokeh?

As we touched on before, bokeh—the out of focus area of the frame—has a quality to it. This is determined by the shape and number of the aperture blades. Typically the more aperture blades a lens has, the better the bokeh is going to be. Also, modern lenses tend to have curved aperture blades while older ones have straight aperture blades which often gives the out of focus areas a pentagonal shape. Telephoto mirror lenses are notorious for having some of the worst bokeh because the light is bounced off a donut shaped mirror which makes the bokeh…donut shaped. (You can just Google “donut shaped bokeh” if you’re curious.)

In this scene from season five of Breaking Bad we can see an out of focus foreground that is made up of a glass being held by Walter White while he talks to his cohort, Jessee. You can clearly see the octagonal shape of an eight-bladed aperture here. Using a shallow depth of field and choosing to include some out of focus areas in the foreground gives depth to the image, there’s a foreground, a middle ground and a background, without distracting from the subject (Jesse). Pay attention during night scenes in movies, especially older ones, and look at the shape of out of focus street, traffic, and car lights, they will take on the shape of the lens’ aperture blades.

Artistic Use or Purposeful Direction?

In this scene from Gary Muldoon vs the Vampires (which I just made up) we have two characters, Gary Muldoon, the sword wielding vampire slayer in the back, and his protegee Kit Danger in the foreground. A director of photography will look at the scene and make a determination on what depth of field to use based on what the scene needs to convey.

If we use a deep depth of field, we see that Gary and Kit are in this together, waiting for the sun to go down.

If Gary is out of focus in the background, then it draws our attention to Kit. What’s she thinking? Maybe of Captain Yurds who has gone off to fetch a load of stakes to fight the night stalkers with; will he make it back in time?

The two options give the Director and the Director of Photography two very different moods and two very different storytelling elements. If they choose to have Gary out of focus, then bokeh becomes an issue – is the out of focus area pleasing? Is it smooth? Is it filled with junk and distractions? Remember, just because an area is out of focus doesn’t mean it’s no longer competing with the in-focus areas. Bad bokeh can clobber all your hard work in setting up a shot by calling attention to itself instead of the subject.

What to Look for in a Lens for Shallow Depth of Field

Luckily, some of the least expensive DSLR lenses have the ability to give you a very shallow depth of field with decent bokeh. The venerable 50mm f1.8, one of the most common lenses, when shot wide open, gives you tremendous amounts of light gathering. So much so that very often it’s difficult to actually get the correct exposure because too much light is hitting the sensor. So with your 50mm 1.8 it’s a good idea to pick up a couple of neutral density filters that will screw onto the front of the lens and block some of the light coming in without affecting its color temperature.

Conclusion

The in and out of focus areas are important to the composition of a frame. You can use out of focus areas to make the viewer pay attention to your subject by removing distractions. Your lens choice is important in creating attractive out of focus areas. Wider apertures create shallower depth of field, but the quality of the out of focus areas are also affected by the shape and number of the aperture blades. Being able to recognize good bokeh puts you on the path for better understanding one of the beautiful subtleties of movie making.

Kyle Cassidy is a visual artist who lives in Philadelphia with his wife and cats.

1 COMMENT

  1. Nice article about bokeh Kyle.

     

    However not everything that you wrote here is correct.

    You wrote: 'Second: the size of your sensor doesn’t affect the depth of field'

     

    Sensor size makes all the difference! For that reason we like to work with a medium format camera like a Phase-One or Hasselblad camera.  Also the difference using 10×8 inch sheet film and 35mm is huge if you compare the depth of field.

     

    Two things mainly effect the depth of field:  aperture and the size of the projected image on the sensor (or film)

     

    Focal length surprisingly has only a very slight effect on depth of field!

    Most people think that a telephoto lens produces pictures with a shallow depth of field, because of the way the image looks.

     

    If you would take a portrait with a 35mm lens with the subject's face filling the same surface of the sensor as with the same headshot using a 300mm from a distance you should measure almost exactly the same depth of field in centimeters.

    The appearance is different because of the distance, but the actually measured depth of field is almost the same.

     

    There a several smartphone apps for calculating the actual depth of field. Check out the parameters.

     

     

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