This bellows features (when used with the Double Cable Release) is automatic aperture operation with Canon FD and FL series lenses.
In addition, it features easy vertical or horizontal use (even with motor drives or winders mounted), easy lens reversal and a host of exciting accessories to greatly expand its usefulness.
CANON DOUBLE CABLE RELEASE
Used with the Auto Bellows, this double-acting cable release permits diaphragm automation with FD and FL series lenses in one smooth operation. Can also be used with extension tubes and the Macro Auto Ring.