One the most fundamental techniques necessary to really to master creative photography is depth of field. It was always a bit of a mystery to me because of the link to aperture and understanding all those back to front f-numbers. I think it was more of a mental block because it is actually quite easy to grasp.
Creatively you are able to do more with your photography and as you learn digital photography you will find using it key to great images. You can use it to blur out backgrounds while the subject remains pin sharp, or, create an image perfectly in focus from front to back as in great landscape photos.
1. What is depth of field?
It is quite simple. It is the amount of a scene that is in focus in front of your point of focus or behind it. Depth of field is more simply understood as, depth of focus. How much of the image is in focus. A lens can only focus at one point which is the sharpest, most in focus point in the photo. But what you can do by using depth of field is to control the perceived zone of focus. This will differ when shooting different subjects or scenes. Now there are three main factors that affect depth of field. Firstly, the aperture you are using, secondly the focal length of the lens and thirdly the focusing distance. All of these will impact the depth of field. Each of these will affect depth of field so in order to control it effectively it’s necessary to master each one of them.
2. Focal length
When shooting an image using a 28mm wide angle lens at say f5.6 you will see a much greater depth of field as compared to a 400mm at the same aperture. So when using different lenses understand what the impact will be so that you can creatively use the resulting depth of field.
On a lens you have possible apertures ranging from f1.2 all the way up to f32 and each of these lens openings will have an effect on depth of field. If shooting on the extremes like F32 you’ll find that it results in quite a considerable difference than when you shoot on f2.8. Then when shooting using the mid-range numbers the depth of field will again be different. An aperture of f2.8 will have a very shallow depth of field while f32 will show sharp focus throughout the whole image.
4. Focusing distance
How far you are to the point of focus is another factor to consider. When using any lens the depth of field will increase the further the focusing distance. If you focus on an object 3 metres away and if you focus on something 300 metres in the distance, the depth of field will be greater. So in other words, the when the subject is far away from the camera there will be a greater depth of field and more of the image will be in focus.
5. When to use depth of field
Most of us have taken landscape images where most of the scene is in focus. This is true when you are shooting scenes of fields and trees and boats on the sea. The way in which this is achieved is by setting you aperture to the highest number, e.g. f22 and above, which means the smallest aperture. Virtually the whole scene from foreground to background is in focus. But this changes when choosing a wide aperture or a small f-number on the lens. Here you would only use this setting to shoot something you want to isolate such as a face in a portrait photo. The background gets blurred out and the face is in crisp focus. You would also use this when shooting close-ups of flowers or animals in a zoo where you don’t want to see the background, or the bars or fence in the foreground.
So as you can see depth of field is really quite simple. Blurred out backgrounds use a large aperture and landscapes that need to be in focus from foreground all the way through to the background, a small aperture. Key to this as you learn digital photography is to experiment with all settings and then practise, practise, practise!
About the Author:
Wayne Turner has been teaching photography for 25 years and has written three books on photography. He has produced 21 Steps to Perfect Photos; a program of learner-based training using outcomes based education.
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