The convergence of light rays to a specific point to form a clear, sharply defined image. In lighting and optics, it also refers to the mechanical adjustment of a lens or reflector to achieve this convergence at a desired distance. When an instrument is out of focus, the light rays scatter over a wider area, creating a blurred image or a soft, diffuse beam.
Heard on the job
Rack the focus on that profile spot until the gobo edges are razor sharp.
Related terms
Focal point
The specific point in space where collimated light rays converge after passing through a lens.
Focal plane
The flat surface perpendicular to the optical axis where an image is sharply formed.
Focus call
The scheduled crew session in which the lighting designer directs electricians to aim and shape every fixture.