Here’s a neat bit of kit from Kessler Crane; a bracket which attaches to their existing slider set-up, that turns the camera, very slightly, as it tracks along the rails.
In other words, instead of the camera simply tracking parallel to whatever you’re filming, you can now aim the camera at a central object (such as an interviewee or the subject of your film) and the camera will continue to point towards it even as the slider moves from side to side.
The suggestion is it (the bracket only, not the whole slide assembly) will retail at around $399.
There’s a great video about it on Vimeo:
Kessler Parallax™ from Kessler Crane on Vimeo.