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Digital Camera Know-Hows
Aperture Value and Expression
Aperture provides two main functions. One is to control exposure. The other is to adjust the depth of field and the image sharpness. A large aperture reduces the depth of field, adding softness to the background. When the aperture size is decreased, the image gains greater depth of field, giving sharp focus to objects from far to near. By varying the aperture size, various photographic expressions can be achieved, such as enhancing the mood and depth of the image, emphasizing the subject, and providing a pan-focus effect to sharply focus on everything from the foreground to the distant background.

Using the aperture setting for exposure control
Similar to the pupil in the human eye,the aperture opens and closes (in the camera's case,a set of blades) to control the amount of light passing through the lens.
  • The larger the aperture opening (f-number: smaller aperture value), the greater the amount of light that passes through it. A smaller aperture (f-number: larger aperture value) restricts the amount of transmitted light.
  • When the aperture is at its maximum opening position, it is referred to as "maximum aperture." Conversely, "minimum aperture" indicates the smallest aperture opening.
The f-number is the focal length divided by the "effective" aperture diameter.
Aperture and light level
Aperture and light level

Here, the shutter speed was kept the same, and the aperture was varied...

smaller aperture value
larger aperture value
Aperture value: F2.8
Shutter speed: 1/125 sec
Aperture value: F5.6
Shutter speed: 1/125 sec
Aperture value: F11
Shutter speed: 1/125 sec
At maximum aperture,too much light turned the image whitish. A smaller aperture size caused insufficient light,making the image dark.

Differences of image expression resulting from different aperture settings
By altering the aperture setting, the depth of field and the sharpness of the image can be controlled for greater photo expressivity.

At the maximum aperture setting, objects located in front of the subject also appear blurry, thus making the subject stand out sharply.
  • A brighter lens with a large aperture (F) value has a shallower depth of field, thus producing greater blurriness.
When the aperture is set at the midpoint, the image starts to become softer at mid-depth, and farther subjects appear blurrier.
Everything from the foreground to the distant background appears sharp.
  • In addition to the aperture, the lens' focal distance affects depth of field. A shorter focal distance for the lens and a longer distance to the subject being focussed will result in greater depth of field. For a pan-focus effect, i.e., to keep everything sharply focussed from foreground to background, use a wide-angle lens and a small aperture setting.
digital camera know-hows