1. Depth Of Field

2. The Depth of Field is a measure of how much ‘depth’ of an image will be in focus.
An image with large depth of field will have much of the image sharp and in focus.
An image with a shallow or small depth of field will usually have only a small part of the image sharp and in focus.
There are three things which can change the depth of field:
The aperture
The focal length of the lens used
How near the subject focussed on is to the camera

3. Aperture & Depth of Field

4. Camera lens focussed on the barbed-wire Large aperture (f2) Note how the background is out of focus.

5. 1. Changing the Aperture
Camera lens focussed on the barbed-wire Small aperture (f16).
Note how whilst not completely in-focus, the background is sharper

6. Large aperture (f2.8) – Note how not all the seaweed is in focus

7. Small aperture (f22)

8. Two photographs from the same position, both with the camera focussed on the wooden beams.
Which image was made using a small aperture and which with a large aperture?

9. Two photographs from the same position, both with the camera focussed on the wooden beams.
Which image was made using a small aperture and which with a large aperture?
Small aperture (f22)
Large aperture (f4)

10. Large aperture Small aperture
One of the problems with using a small aperture to get maximum depth of field is that to get the correct exposure a much slower shutter speed may be required. This has led to a problem in the right hand image …

11. Large aperture Small aperture
The right hand image was taken at a slow shutter speed (1/30) to get correct exposure and because of this the moving fishing net has become blurred (motion blur).

12. 1. Where was the camera focussed for both images. 2
1. Where was the camera focussed for both images? Which image was made with a small aperture and which with a large aperture?

13. There are two other variables which also alter the depth of field:
2. Focal length of lens
Long focal length lenses (telephoto lenses) have less depth of field than short focal length lenses (wide angle lenses).

14. F16, 1/250 of a second 24mm (wide angle) lens F16, 1/250 of a second
100mm (telephoto) lens
(To take this picture I had to stand much farther away from the car to get a similar composition)

15. 3. Distance of subject to the camera
The nearer you are to the subject which you focus on, the smaller the depth of field.

16. Three images taken with the same lens and exposure, each focussed on the car.
f5.6, 1/500 second
Camera close to car
f5.6, 1/500 second
Camera further from the car
f5.6, 1/500 second
Camera even further from the car.

17. SUMMARY Depth of field is affected by THREE factors:
The aperture (small apertures give more depth of field)
The focal length of the lens (shorter focal lengths give more depth of field)
The distance from the camera to the subject focussed on (the greater the distance the greater the depth of field).
Chris Monaghan