The updated version of the EF-S 18-135mm f3.5-5.6 IS lens incorporates two important features. First, it incorporates the new Nano USM (ultrasonic motor), intended to combine the still-focusing speed of the pro lenses with the quiet video operation of the current STM (stepper motor) lenses. Second, it's the first lens to have connectors for the new power-zoom adpater.
The adapter provides a camcorder-like zoom switch that you operate with your left thumb. You can set zoom speed and disable it for manual zoom.
These are the connectors where the power-zoom adapter fits to the lens. There are two notches on the sides where it locks in.
This is where the adapter connects to the bottom of the lens.
The power-zoom adapter is somewhat large, but it's a good size to pair with this lens.
The adapter runs on four AA batteries.