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Shift Lens disabled (left) and enabled (right) to allow capturing the entire building while keeping the camera level, thus creating parallel vertical lines
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After you have leveled the camera, you should navigate the camera in the viewport only by panning (Alt+MMB) to avoid rotating it up/down and thus creating a three-point perspective again. Once you have the view you want, use the Shift Lens parameters to move the frame up/down/left/right. It acts like percentage of the size of your image, so a 100% shift in the Y axis will offset the image up exactly the height of the image.
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