Motorized pot
These motorized pots are extremely cool! They contain a 20kΩ potentiometer, connected to a DC motor via a gear assembly and clutch (for manual turning). While I assume that these were originally intended for applications such as a motorized volume control on a stereo, they're just perfect for this project. And if this wasn't enough, they were very cheap at the Electronic Goldmine.
Exposure Time: 1.6 sec • F-Number: f/8.0 • ISO Speed Rating: 100 • Focal Length: 16.40 mm