I understand how to use asymmetric movements. I think I understand how they work as well: when you tilt or shift the rear standard, it's arranged such that the axis of the tilt/shift passes through the ground glass right along the marked lines. That means that line along the ground glass remains stationary, so of course its focus won't change as the distance to the lens of that particular slice of the image doesn't change.
What I don't quite understand, though, is why it's necessary for these axes to be offset towards the edges of the image. With a camera that tilts/shifts around the center of the film plane, couldn't you simply line your subject up along a center line and then repeat the same procedure you use on a camera with asymmetric movements? Are the offset axes just there because it's usually more convenient for composition purposes to use an object closer to the edges of the frame?
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