Known for their industry leading camera sliders and portable jibs, Kessler continues to innovate by creating useful products for filmmakers. Their latest creation is called the Parallax, and in this video, Eric Kessler demonstrates how it works to create a motor-less, controlled panning action on your existing slider. This can make a move where during your camera's horizontal move, the head pans to stay with its subject.
Having tried several times in the past to pan the camera manually during a slider shot, I know how hard it is to pull off smoothly. The fact that it's an easy add-on to an existing rig that many people have is another awesome bonus for making this a very slick accessory.
The Parallax isn't expected to start shipping for a few months, and it's projected to cost about $400. There aren't any details on the Kessler website yet, so check out the video description on Vimeo for what little information is out. Here is the list of sliders that Parallax should be compatible with:
"Traveler and standard length Pocket Dolly v2.0 BASIC, Pocket Dolly v2.0, Stealth & Philip Bloom Pocket Dolly as well as the traveler, 3' & 5' CineSlider."