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Selecting an Aperture
A discussion of how to select an appropriate aperture boils down to an explanation of depth of field. When your subject is in focus, there is only a limited range in the foreground and background of the subject which is also in focus. This zone of sharpness is called depth of field.
Depth of field is governed by three factors: aperture, lens focal length and shooting distance. Remember the following relation- ships:
(1)The smaller the aperture, the deeper the depth of field (the other two factors remaining the same).
For example, if the lens focal length and the shooting distance stay the same, the depth of field is much deeper at f/16 than at f/1.4.
(2)The shorter the lens focal length, the deeper the depth of field (the other two
S Aperture priority AE |
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FD 300mm f/2.8 S.S.C. FLUORITE, f/2.8 ASA 125 |
factors remaining the same).
For example, comparing a 28mm lens with a 50mm lens at the same aperture and shooting distance, depth of field is deeper with the 28mm lens.
(3)The greater the shooting distance, the deeper the depth of field (the other two factors remaining the same).
For example, if the subject is photo- graphed from three and then from seven meters away, the zone of sharpness in the foreground and background is great- er at seven meters.
Another characteristic of depth of field is that it is generally deeper in the background than in the foreground.
When depth of field is important in your picture, it is best to control the aperture directly using the aperture priority AE mode. Using a small aperture is great for getting sharp overall focus in a landscape or any other type of subject, but shallow depth of field also has its merits. Using a relatively large aperture will make your subject stand out against its surroundings by blurring the background. This is an especially successful technique in portraiture and special effects.
There are ways to check the extent of depth of field. For this information, please refer to page 76.