For context: a barn door tracker is a simple DIY device – essentially a hinged arm driven by a servo-actuated screw – that can be used to counteract Earth's rot

For context: a barn door tracker is a simple DIY device – essentially a hinged arm driven by a servo-actuated screw – that can be used to counteract Earth's rotation and thus keep objects in the night sky from drifting too much within the field of view of a camera. This allows for long exposure times (minutes or tens of minutes) which are more or less mandatory when imaging dim objects with a telephoto lens.