This DIY motorized zoom for a dSLR camera has been built to be used with the eMotimo TB3 for use with time lapse phototography. Specifically, I plan on using this to create vortex star trails of the night sky. Although there are ways to do this in Photoshop, I wanted to try and build a rig that would slowly zoom the lens in between each shot. The eMotimo TB3 allows for a external stepper motor that is usually used in motion slider photo ro video sequences, but I'll be using this to drive the gears to spin the zoom. I would assume that you could use this with other time lapse rigs that allow a shoot-move-shoot sequence. Most of the parts are Actobotics from ServoCity.com.
This could also be used as a motorized follow-focus rig with a little tweaking. I'll be using it specifically for astrophotography for now. If I ever pull the trigger on the new eMotimo Spectrum, I'd be able to do a motion time lapse with zoom or variable focus. Sounds fun!
(ServoCity.com Parts Only)