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henry albert wrote:
Well, no. Depth of field cannot be changed by cropping or resizing. The die is cast when the shutter clicks. Every action after that is irrelevant in terms of DoF.
Please acquaint yourself with the concept of COC. What you say is not true and can easily be understood by looking at how DOF is determined using the concept of COC. DOF is NOT a fixed thickness of a plane where everything is sharp and which is not changing by cropping, changing distance aperture etc., but is the depth that APPEARS to be in focus. The larger you display the image, the more obvious it will become that deviations from the "plane of perfect focus" are out of focus, and the smaller you display the image, the less obvious it will be. So what is appearing to the human eye to be in focus is dependent on viewing size (and therefore cropping and magnification) and distance to the print/image, which is used to define COC, which then determines the DOF.
The link above deriving the DOF formulas shows in its first images the rear and front part of the DOF-zone. This zones is determined by defining a blur circle formed by the light rays penetrating the sensor plane, with a size that is seen by the user still as a point, ie. is smaller than the COC. So cropping and magnifying your image will change these relations, as the point formaly seen as sharp could be seen as blurred now or vice versa and therefore the depth of the region where everything is in focus changes.
Look here, too:
http://www.josephjamesphotography.com/equivalence/#dof
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