Movie Making Manual/Special Effects
Often what people believe to be SPECIAL EFFECTS (SPFX) are computer generated VISUAL EFFECTS (VFX). This confusion results from the final products of both departments looking similar. Visual effects may involve computer animations, green or blue screen compositing or other post effect work. VFX may highlight or multiply the SPFX shots to create a much larger explosion for example.
Introduction to Special Effects for film
SPFX Technician Dean Campbell states that "special effects are basically any on-screen physical effect that is not done by the actor". This can mean atmospheric effects such as smoke, wind, rain, haze or simulated conditions such as boiling pots, exploding cars or campfires.
This also includes any movement of objects in front of camera such as falling dishes, floating furniture or breaking glass.
Often the PROPS DEPARTMENT will claim to do special effects, however under IATSE regulations props are items used or touched by the actor.
Concerning situations that call for department overlap, the above guidelines still apply; for example if a scene calls for an exterior shot of a snow covered street with gently falling flakes it would be the responsibility of the set dresser and greens department to dress in snow, but the responsibility of the special effects department to create the falling snow effect.