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The double-arm barn door tracker (jlab.org)
31 points by Tomte on Aug 18, 2022 | hide | past | favorite | 10 comments



> 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


And here I was thinking it was a way of checking if the barn door was open, and how much, and was thinking "why not just reset it at closed".


why not just reset it at closed

If the horses are gone, there’s no point?


#1 rule of software development is always closing the barn door after the horses have left.


With reference counting, the doors can open as each horse escapes, and close after them automatically while no horse is escaping.


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.



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...


Yes, because curving a bolt with the appropriate radius is such an easy thing to do. /s




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