Pentax 18981 - Ist D Igital Camera SLR, Руководство по эксплуатации

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The aperture increases or reduces the light beam (thickness) which
passes through the lens, controlling how much light strikes the CCD.
• Widening the beam by opening the
aperture
Objects closer and farther than the focused
subject will be more out of focus. For instance,
if you take a picture of a person against a
landscape with the aperture open, the
landscape in front of and behind the person
will be blurred, emphasizing only the person.
• Narrowing the beam by closing the
aperture
The range in focus expands forward and
back. For instance, if you take a picture of
a person against a landscape with the
aperture narrowed, the landscape in front
of and behind the person will be in focus.
Effect of aperture
• When you focus on a portion of the subject, there is a range in which object
closer and farther will also be in focus. This focused range is called the depth
of field.
• As the aperture is stopped down, the depth of field (focused range) increases
(wider range of focus).
• Also, the wide-angle lens, and the farther away the subject, the wider the
depth of field.
• Zoom lenses do not have a scale for depth of field because of their structure.
• The depth of field for the
w differs depending on the lens but, compared
to when using a 35mm camera, the value is roughly one aperture setting
lower (the focused range becomes narrower).
Further, check the depth of field at one stop open side for lenses with a depth
of field scale.