Plane of focus
In a normal lens, your point of focus occurs in a plane parallel to the sensor, so if you focus on a point five metres away, for example, then everything in that five metre plane will be sharp. With tilt-shift, we can skew the plane of focus one way or another. It lets us either create a really narrow band of sharpness – often used for toy-town miniature effects. Or alternatively, we can angle the plane of focus across the face of the subject to produce greater sharpness, even at the widest apertures. This can be particularly useful when shooting video, as it means depth of field can be extended without having to ramp up the ISO.