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Message: <blockquote data-quote="Dave_W" data-source="post: 122958" data-attributes="member: 9521"><p>In fact, the reason you know the focal lengths do not change between FX to DX is that the lens has a very specific place in which the light rays all converge. And it is at that exact point that you must place the sensor. If you move the sensor forward or backward relative to that single focal point your images will be out of focus. The lens is designed to focus all the light rays at that single point irrespective of the camera body. And it is this focus point that creates the measurement of focal length. Therefore focal length is dependent upon the lens and has nothing to do with the camera or sensor.</p></blockquote><p></p>