Lesson 3: Depth of Field

Kozak02Depth of Field
by Steve Kozak
M. Photog., CR.
CPP

 

 

 

Depth of field is defined as “the area in a photograph that will be in acceptable focus.”

Simply put, depth of field determines the relative sharpness or lack of sharpness in the background (and the foreground) in relation to the subject.

This image has enough depth of field in front of the subject to keep some of the framing elements in the foreground sharp, while not extending too far behind the subject to allow the background to go soft.

Depth of field is a measurable distance. Approximately one-third of the total distance extends forward towards the camera at the point of focus and two-thirds extends behind the point of focus. For example, with a subject focused at 10 feet with a 9ft depth of field, the photographer can anticipate relative sharpness between 7 to 16 feet. (3ft in front, 6ft in back)

There are three things that control depth of field:
• F-stops
• Camera-to-subject distance
• Focal length of the lens

Controlling the depth of field allows the photographer to “soften” or “sharpen” the background and foreground to the degree that is desired for the specific image. A shallow depth of field helps to put emphasis on the subject and may help to eliminate unwanted distractions.

F-Stops
The f-stops not only control the amount of light that reaches the sensor, but they also control depth of field.
dof3

dof1 Shallow Depth of Field
A shallow DOF means that the background and the foreground will appear more out of focus.

The image at right was taken at F2.8 and has a shallow depth of field. Notice how the background is quite out of focus.

This technique allows the photographer to place the emphasis on the subject without distractions from the background.
dof2

Large Depth of Field
With a large DOF, the background and the foreground appears sharper or more in focus.

The image at left was taken at F16 and has a much larger depth of field.

A larger depth of field is useful when elements in the background are used as part of the overall composition.

Camera-to-Subject Distance
The camera-to-subject distance has a pronounced impact on depth of field.

The closer the camera is to the subject, the shallower the DOF.
The further the camera is from the subject, the greater the DOF.

Focal Length
There are inherent tendencies in lens selection to depth of field.

The longer the focal length of the lens, the shallower the DOF.
The shorter the focal length of the lens, the greater the DOF.

Photographers Choices and Depth of Field
The photographer who is looking to gain as much depth of field as possible will tend to utilize wide angle lenses, a greater camera to subject distance and small lens openings.

The photographer who is looking to create minimal depth of field will utilize a combination of large lens openings, longer telephoto lenses and getting close to the subject.

Calculating Depth of Field
This task was much simpler in the days when lenses had a depth of field scale etched into the barrel of the lens. With many of today’s modern zoom lenses used on so many cameras of varying sensor sizes, the depth of field scale has virtually vanished.

There are a number of online DOF calculators and some printed charts available which are camera specific, but the easiest way to calculate DOF these days is with a helpful smart phone app. (I use Depth of Field Calculator BY Essence Computing.)

The DOF calculator in not required for and would not be allowed in taking the CPP Exam.  You will be given the necessary details required to answer any questions on DOF.

Welcome to your Lesson 3: Depth of Field

1. The f-stops serve two purposes - what are they?
2. What is Depth of Field?
3. Why would you want to move the lens from F4 to F2.8?
4. If you move the f-stop from F5.6 to F8, what happens to the amount of light that reaches the sensor?
5. If you move the f-stop from F5.6 to F8, what happens to the depth of field?
6. What happens to the depth of field when you move the lens from F11 to F16?
7. What happens to the amount of light reaching the sensor when you move the lens from F11 to F16?
8. If you are photographing with a 50mm lens, which camera-to-subject distance would create the largest depth of field?
9. Which lens would provide the photographer with the best option for a shallow depth of field?
10. If you are photographing with a 200mm lens, which camera-to-subject distance would create the shallowest depth of field?