Better Video Through Bokeh & Depth of Field (Camera Lesson 04)

Summary: How you creatively use bokeh and depth of field can influence how your audience feels about the films images you create. In this video Ryan covers what these terms mean, and how to use them in filmmaking.

Length: 3:41 minutes

Video Lesson

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Transcript

Introduction

Now that you’ve mastered the six essential terms to understanding digital cameras, in this video I’ll be covering two important terms that affect the aesthetic of your image: bokeh and depth of field.

Bokeh

Bokeh defines the out of focus areas of the of the image. There are different types of bokeh. Sometimes it will be nice and smooth, sometimes there will be hot spots in the center, and other times there will be hot spots on the edges.

It is the build quality of the lens that affects the look of the bokeh the most. The aperture has a direct impact on how round it looks. The more blades there are in the aperture, the rounder it will look. The less blades, the more polygon it will look. There are even some older lenses that have a triangular shaped bokeh.

How a lens corrects for spherical aberration also impacts the look of the bokeh. In an ideal lens all light rays will converge into a single point. In a less precise lens, those light rays converge at different points and that affects how the bokeh is rendered.

What determines good bokeh has a lot to do with personal taste. But generally speaking good bokeh is bokeh that …

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3 replies
  1. aurelienbrentraus
    aurelienbrentraus says:

    Hi, I am a little confused here, please correct me if i am wrong. I think the depth of field is totally dependent on three factors: focal length, distance to the subject, and aperture.

    For example if we shoot with 100mm at f1.4 from 10 feet distance and the same subject we shoot with 50mm f1.4 from 5 foot distance the depth of field will be the same. The pictures might look different because of angle of view, the bokeh will be different based on angle of view, depth of field also depends on sensor size as well. The bigger the sensor the shallower depth of field.

    Reply
    • Ryan E. Walters
      Ryan E. Walters says:

      You are on the right track and mostly correct (98%).

      Contrary to popular belief, Depth of Field (DoF) doesn’t actually change depending on sensor size. A 50mm lens at a T1.4 focused at 5 feet gives you a DoF of (roughly) 2 inches regardless of if you are shooting on a full frame camera or a micro 4/3 camera. I say “roughly” because the Circle of Confusion also factors into how the DoF is perceived. (I also touch on this a little in the video on lenses when I mention that a 50mm lens is always a 50mm lens.)

      The reason why people say sensor size has a big impact on the DoF, and why it seems that way as you use your camera, is because most of the time we are trying to get a similar image (angle of view) out of both cameras. If you put a 50mm lens on a full frame camera (5D), frame your subject at 5 feet at a T1.4, (DoF = ~3 inches) and then you take that same 50mm lens and put it on your Micro 4/3 camera (Blackmagic Pocket Camera) and you try to get the same angle of view, you have to back up about 3x the distance, or to about 15 feet. Since you have just backed up, your subject distance has changed, which increases your DoF to ~10 inches.

      Of course, for ease of communication, it is simpler to just say “smaller sensors have a greater depth of field” because functionally speaking that is what ends up happening. 🙂

      Cheers,
      Ryan

      Reply

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