The double-arm barn door tracker

> A barn door tracker, also known as a Haig or Scotch mount, is a device used to cancel out the diurnal motion of the Earth for the observation or photography of astronomical objects. It is a simple alternative to attaching a camera to a motorized equatorial mount.[1]

[1]: https://en.wikipedia.org/wiki/Barn_door_tracker

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.

He developed it in the 1980's to do an astro-photography on the cheap (cheaper than equatorial mounts). Used a Commodore 64 at the time to run the numbers — presumably find out the tangent error deltas for various relative arm lengths.

I suspect a simple spreadsheet today could be constructed to give the same results. Maybe even a clever graph of error over degree.

Video I found on YouTube:

https://www.youtube.com/watch?v=Z-20j49UNbM

There's another simple way to decrease tracking error for a barn door mount, and that is to use a curved bolt with an appropriate radius of curvature. See Gary Seronik's 2007 article [0].

[0] https://garyseronik.com/a-tracking-platform-for-astrophotogr...