If you photographed in pre-digital days and used a large-format camera, you knew the Scheimpflug Principle. Sounds daunting and takes some getting used to, but basically, the front part that held the lens and the back part that held the film did not have to be fixed and parallel to each other (which they are in almost all cameras). In a normal camera, if you change focus, the sharpest areas are simply nearer or farther away, and depth of field goes from near to far also. Not so if you tilt either the lens or the back. The plane of focus, which you can imagine as a sheet of glass upright in front of and facing you, tilts away as you tilt the lens forward. Why? Because what you may want sharp in the image isn’t necessarily from near to far ...

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