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Message: <blockquote data-quote="Eyelight" data-source="post: 326431" data-attributes="member: 24753">Well, from a lens point of view, changing focal length is not the same as changing focus distance, but from the camera's point of view changing focal length is pretty much the same thing as changing distance.Main thing is the real world application is: When framing a subject the same size, the same aperture produces nearly  the same depth of field at different focal lengths.  If a bird that occupies 50% of the view and fits in the DOF at f/11, the bird will fit in the DOF at 50% view and f/11 at all focal lengths.</blockquote>