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Old Jul 18, 2010, 7:28 PM   #1
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Default What causes some subjects to be out of focus?

I'm a beginner so just trying to understand why some subjects that are in the same plane and not in the background would be out of focus? I am using a Canon T1i and 70-200f4 IS lens. I am assuming it's from camera shake? I did not use a tripod.
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Old Jul 18, 2010, 7:33 PM   #2
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Example?
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Old Jul 19, 2010, 2:41 AM   #3
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An example would help but I suspect objects need to be the same distance fron the lens, which is not the same as being in a plane. Think more of the curved surface of a sphere.

Camera shake would affect the whole image. It could be that you were steady and some of the subjects were moving though. But that should be apparent in the photo because there will be some direction to the blurring.
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Old Jul 19, 2010, 2:54 AM   #4
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Quote:
Originally Posted by MartinSykes View Post
An example would help but I suspect objects need to be the same distance fron the lens, which is not the same as being in a plane. Think more of the curved surface of a sphere.

Camera shake would affect the whole image. It could be that you were steady and some of the subjects were moving though. But that should be apparent in the photo because there will be some direction to the blurring.
It depends on the lens if it has a flat or curved focus plane but I believe the 70-200mm f4 is flat.

An example of a photo with the problem will help but likely it is just that the DOF is so shallow even being a few inches out makes a difference when at f4.
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Old Jul 19, 2010, 12:00 PM   #5
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Quote:
Originally Posted by gavsmompa2 View Post
I'm a beginner so just trying to understand why some subjects that are in the same plane and not in the background would be out of focus? I am using a Canon T1i and 70-200f4 IS lens. I am assuming it's from camera shake? I did not use a tripod.
If you have just moved from using a P&S or bridge camera, you will
find that the T1i will tend to produce images with a much smaller
depth of field, particularly when you use a fairly long focal length
lens like the 70-200.

Try using a smaller aperture (bigger F number) to increase the depth
of field. This will require a longer shutter time (more camera shake)
or higher ISO setting (more noise), so you might need to use a
tripod in some situations.

Some sample images with EXIF information intact would help
us to diagnose the problem.
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