Ellipsoidal spotlight use a special reflector to collect and direct the light through a barrel that contains a lens or lens train. Adjusting the tube by pushing it further in or pulling it further out of the unit allows changes to the focus. Ellipsoidal lights are used in theatre, nightclub, light design and movie / TV production. Ellipsoidal reflectors are used for their strong, well-defined light and their versatility.
Ellipsoidals are supplied with a certain size lens or lenses that determines the field angle, anywhere from five to ninety degrees. Field angle is the angle of the beam of light where it reaches 10% of the intensity of the center of the beam.