Depth of Field, Part 2:

How Focal Length, Distance, and ND Affect Depth of Field

Written and presented by Scott Ballard

Summary: In Part 2 of our series on depth of field we cover how the focal length of the lens and the distance from the subject affect depth of field. We also cover how you can use neutral density filters (ND) to control light levels so you can achieve your desired depth of field.

Length: 5:41 minutes

Video Lesson

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Transcript

Introduction

In the last lesson we covered how to control depth of field using aperture and ISO. Here are two more useful tools at your disposal that will aid in being able to control your depth of field. They are distance or lens focal length and ND (neutral density) filters.

Lens choice and distance affect depth of field
We can make our lens choices determining two factors – how close we want the camera to the subject and how much of the frame around our subject we want to see.

Focal length of lens affects depth of field
The larger the subject, in this case the cup of coffee, is in the frame, the shallower the depth of field will be behind the cup.

Distance from subject affects depth of field
Remember that each lens has a minimum focusing distance, meaning that it can only focus on an object as long as the camera is set a certain distance from the object. This will depend on which lens you are using and is usually marked on the lens. If a subject is closer than the minimum focusing distance, critical focus cannot be obtained.

Depth of field is affected by focal length of lens.
Prime lenses have a fixed focal length, whereas a zoom lens is able to adjust or zoom through a variety of focal lengths. Typically prime lenses are faster (meaning their aperture opens up further) and there is less light lost in the lens as there are less glass elements through which the light is passing. And as we saw in previous episodes, this can have an effect on depth of field.

A 14mm prime lens requires being closer to subject to have narrow depth of field
Using prime lenses allows the distance between the camera and subject to change, depending on if we are using a wide angle or telephoto lens. A wide angle lens would be around a 24mm or 14mm lens.

Distance is limited by minimum focus distance
If we use a 14mm, you’ll see that we introduce quite a bit of the world. The wider the lens, the smaller the minimum focusing distance – therefore we can get very close to our subject. Now the camera is much closer to the cup. Notice that our depth of field has now narrowed, since the subject is closer to the lens and larger in the frame...

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Tools We Used

Depth of Field, Part 5: How Circle of Confusion and Diffraction Blur Your Image
Depth of Field, Part 4: Using a Depth of Field Calculator
Depth of Field, Part 3: Hyperfocal Distance
Depth of Field Part 2: How Focal Length, Distance, and ND Affect Depth of Field
Depth of Field, Part 1: How Aperture and ISO Affect Focus
Your Guide To High Speed, Part 6: Five Tips For A Successful Shoot
Your Guide To High Speed, Part 5: Lighting Six High Speed Sets
Your Guide To High Speed, Part 4: Common Lighting Problems
Your Guide To High Speed, Part 3: Camera Operation & Workflow
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