Stop motion animation reached the height of its popularity during the 1950s. The exploding popularity of science fiction films led to an exponential development in the field of special effects, and George Pal became the producer of several popular special effects-laden films. Meanwhile, Ray Harryhausen's work on such films as "Earth vs. the Flying Saucers, The Seventh Voyage of Sinbad", and "The Beast from 20,000 Fathoms" drew in large crowds and encouraged the development of "realistic" special effects in films. These effects used many of the same techniques as cel animation, but still the two media did not often come together. Stop motion developed to the point where Douglas Trumbull's effects in "" seemed lifelike to an unearthly degree.