Animation of gravitational lensing over the Hubble Deep Field North. Gravitational lensing occurs when a massive object lies between Earth and a much more distant object. The gravitational field of the middle object the lens bends the path of light from the more distant object, resulting in an observer seeing distorted images, multiple images or, in the case of a perfect alignment, a ring called an Einstein ring. The Hubble Deep Field HDF is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope.