From the manufacturer's official website:

With a new arm actuating the parallelogram, the Centaur™ 2007 QS™ front derailleurs allow riders snappier and lighter shifting. They need to be interfaced with the left-hand Ergopower™ QS™ controls and are available in two versions: for standard cranksets and for compact cranksets.

For double standard crankset: capacity 15 – max. chainring 54 - min. chainring 39- antifriction insert.
Nominal weight: 86 g.

For CT™ compact crankset: capacity 16 – max. chainring 50 - min. chainring 34 - antifriction insert.
Nominal weight: 95 g.

For more information, please visit this product's webpage.