The HA-77 Horizontal Extension Arm / Boom Arm from Sirui is a versatile accessory arm for macro photography, mounting dual tripod heads, and more. It features an arm that can be extended in length from 19.7 to 30.3" with the use of a simple twist-lock joint. Each end of the arm can receive a tripod head by way of a reversible 1/4"-20 to 3/8"-16 mounting stud. One end can also be converted to use the included ballast hook for added counterbalance when extending a heavy camera.
The angle of the arm can be adjusted +/-90 degrees, and then locked in place with a robust knob. A numbered angle scale allows precise and repeatable results. The arm can also be laterally positioned with ease, and features a numbered scale. The entire arm mechanism is mounted on a sturdy panoramic base with a 360-degree rotation capacity and an independent locking knob.