Lesson 2: Depth of Field
Depth of Field refers to the area of the image [or field] that will be in sharp focus and the distance from the lens that objects will be in sharp focus.
In the diagram below:
D is the distance from the lens where there is the sharpest focus
S is the acceptable sharpness of focus -- anything less focused will appear blury
E+E is the range of acceptably sharp focus, the distance before and after the point of sharpest focus where objects are acceptably in focus.
To control the depth of field [the location and range of sharp focus], the photographer uses two elements of the camera: the f-stop and focus.
The higher the f stop [e.g., f22, f18] the smaller the lens aperature and the greater amount of the field that is in focus.
The smaller the f-stop [e.g., f3.6, f4.0, f5.6] the smaller amount of the field that is in focus.
In all cases [for all f-stops], the focus feature of the camera determines where the point of exact focus of the image will be: close to the photographer, in the middle of the field, or far from the photographer.
Automatic cameras try to keep everything in focus [e.g., they use high f-stops] or they balance the f-stop, the point of exact focus, and the shutter speed to get as much of the image in focus as is possible. Thus, in Example 1 below, an automatic camera would lose the special effect that is gained by having only the boy in the field of sharp focus. To control depth of field, you need to learn to use your camera on manual settings which means that you select the f-stop, the sharpest focus point, and the shutter speed.
Example 1: For photographic effect, only the boy is in the field of sharp focus which is close to the camera. Can you guess from the discussion above whether a high f-stop or low f-stop setting was used in this shot? |
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Example 2: Only the church steeple in the far distance is in the field of sharp focus. Was a high or low f-stop used for this shot? |
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Example 3: Only the flower, very close to the lens is in focus. The field of focus is very small. Was a high or a low f-stop used for this shot? |
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