The visual effects for "Stargate SG-1" and "Stargate Atlantis" are predominantly produced by Rainmaker Digital Effects, a notable visual-effects studio. However, some effects, including the entire Ori battle sequence in the episode "Camelot", were done "in-house". The unstable vortex effect, both in the film and the early seasons of the series, on account of being "difficult to achieve" was generated only once and recorded from various angles; this recording was the same used for all gate opening shots early in the series. Rather than being a jet of water, it is actually the image of high-pressure air being blasted "into" a tank of water. The effect was achieved by mounting a jet airplane engine two feet above a water tank, and using its windstream to create the sufficient water displacement. In post production, the surrounding water was removed with computer editing, and the image of the air-jet pasted into the center of the opening stargate. This technique was only used for earlier episodes, and the effect was replicated digitally soon after to allow more flexibility in shots.