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Old Mar 7, 2010, 8:49 PM   #11
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A smaller aperture number (f2.8) means that the lens opening is bigger and will let in more light than a larger number (f8). A lens is usually sharper when "stopped down" a bit, letting in less light. For many lenses f8 - f11 is the sharpest apertures (it varies from lens to lens).

Exposure is based on 3 different factors - aperture, shutter speed and ISO. If you increase ISO (make the sensor more sensitive to light) and you use a faster shutter speed, your aperture doesn't have to change - it can stay the same. With your Sony, set the ISO to 200, use Av mode and set the aperture to whatever you used here and your shutter speed will have to be faster in order to keep the same exposure.

Aperture controls what they call depth of field - a larger aperture (smaller number, like f2.8) will have a smaller depth of field and a smaller aperture (like f8) will have a bigger depth of field - i.e., the distance from the minimum focus to the maximum point where the picture is still in focus. That means that a lens might have half a foot in focus at f2.8 and 6 feet at f8. Focal length also influences depth of field, but that's another story.
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Old Mar 7, 2010, 9:49 PM   #12
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Check out this site, it has one of the best illustrative interactive explanations Ive seen.
http://www.ted.photographer.org.uk/p...ce_control.htm
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Old Mar 8, 2010, 12:27 PM   #13
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what is the advantage of large aperture if you get sharpness and dof with smaller aperture? Could you give an example from real life situation? I believe with large aperture you would get most light from the place so it says me i need to use it indoor or night pictures, is there any other examples?
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Old Mar 8, 2010, 1:01 PM   #14
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You can use a wide aperture to control your depth of field. Taking a portrait outside and separating the background by making it out of focus is a use of wide aperture. For the portrait you might want focus depth from the nose to the ears and everything behind out of focus. Knowing what you want and how to best get it, is the learning process to becoming a photographer instead of a picture taker.
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Old Mar 8, 2010, 2:57 PM   #15
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Quote:
a larger aperture (smaller number, like f2.8) will have a smaller depth of field and a smaller aperture (like f8) will have a bigger depth of field
but you say "wide aperture to control your depth of field", a little bit confused, will i get dof with large or small aperture?
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Old Mar 8, 2010, 4:26 PM   #16
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Quote:
Originally Posted by imut View Post
but you say "wide aperture to control your depth of field", a little bit confused, will i get dof with large or small aperture?
The smaller the aperture (i.e. the larger the number) the greater the depth of field. Keep in mind that DOF is more critical at closer distances than farther away. Perhaps you want to blur a background behind your subject? Use the larger aperture.

In addition when you purchase a lens, read a good review. They will inform you about the quality of the lens at wide apertures. Some lenses are pretty sharp even at the largest aperture.

Dave
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