Barn doors

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A set of barn doors are on the right. On the left is a "top hat" or "snoot", another method of controlling light output on a fresnel lantern

Barn doors, or colloquially a set of barn doors, are an attachment fitted to the front of a Fresnel lantern, a type of spotlight used in films, television, and theatres. The attachment has the appearance of a large set of barn doors, but in fact there are four leaves, two larger and widening on the outside, two smaller and getting narrower towards the outside. They facilitate shaping of the beam of light from the fixture, and prevent the distinctive scatter of light created by the Fresnel lens from spilling into areas where it is not wanted, such as the eyes of audience members.

Barn doors are mounted with a ring that fits inside of the color gel slot on the instrument. Because of this, barn doors have a gel slot built in to them, so the light can still be colored. Depending on the size and local practices, barn doors may be attached to the pipe or the instrument with their own safety cable.

Barn doors are generally not used with 'profile' or 'Ellipsoidal reflector spotlights' such the Source Four because they have internal shutters which work more effectively. Barn doors are ineffective for shaping on PAR lights, but may be used to control lens flare in place of a snoot.