Tilted plane focus

Focus is relative to spatial depth. Selective focus in photography is usually associated with depth of focus. A pinhole generates an image of ‘infinite’ relative focus from a point just outside the opening out to infinity. Lenses focus more selectively so that for objects near the lens the distance between lens and sensor or film is increased, and is shortened for more distant objects to a point beyond which all is in focus. In telephoto lenses this point may be tens or hundreds of metres from the camera. Wide-angle lenses distinguish differences in depth only up to a short distance beyond which all is in focus.