In this area, motorized carts travel along 30-foot rails, allowing astronomers to adjust the length of the light path in real time. This adjustable section of the light path is called the Fast Delay Line.

Read the transcription from the related video: "Steering the Light"

The following are descriptions of locations in the panoramic image.

Location 1 - Beam splitters
Optical devices that use controlled reflection to produce two beams from a single beam.

Location 2 - Delay Line Carts
Each of these motorized carts carries three mirrors. Astronomers can adjust its position along the rails to control the length of the light path to within 1 millionth of an inch.

Location 3 - Fast delay line rails
The Delay Line Carts travel along these 30-foot rails to adjust the path length of incoming starlight.