Possible Duplicate:
Technically, why is the out of focus area blurred more when using a bigger aperture?
Why is it that a larger lens aperture produces a shorter depth of field, causing the background of a photo to be more blurred?
Possible Duplicate:
Technically, why is the out of focus area blurred more when using a bigger aperture?
Why is it that a larger lens aperture produces a shorter depth of field, causing the background of a photo to be more blurred?