During the morning two radar operators at a missile tracking site caught a fast-moving object on their scope. At the same time a tracker watching a B-29 with binoculars saw a large UFO near the bomber. Another observer sighted the UFO and, with a 35 mm camera, shot 200 feet of film.

The UFO showed on the film as a round, bright spot. (The film has never been released.) source:

http://www.nicap.dabsol.co.uk/sands.htm