Has anyone built or purchased a barn door for astrophotography?
Got any suggestions?
I'd like to purchase an inexpensive motorized one. Any recommendations?
They also seem to be pretty simple to build on your own. I don't have much experience building mechanical things though, so any tips on how to do it and what all is involved?
I've not got round to building my own tracker yet, one day! But I can recommend a great little book I've got which deals with this , I don't know whether its in print or not anymore, I got mine secondhand via the Internet:
"Handbook For Star Trackers" by Jim Ballard, published by Sky Publishing Corp, ISBN 0-933346-47-6 in 1988. The sub-title for the book describes it as " Making and Using Star Tracking Camera Platforms". I can't remember what I paid for it, but it was very inexpensive indeed.
I've been considering making one of these. There's quite a lot of DIY info online, just google for barn door tracker. The simplest versions use just two planks, a piano hinge, and a manually turned threaded rod. They aren't accurate enough for long exposures, but for long exposures you need very accurate polar alignment anyway, and I'm thinking it makes more sense to start with a simple mount and just stack exposures.
When you start looking, you'll see talk of "tangent drive", "isosceles drive", and "dual arm" versions. These have increasing accuracy assuming a constant drive rate. Note that you can simply vary the drive rate to get perfect theoretical accuracy out of even the simplest version, so there's no reason to go with the more complex models unless you're going to put in a constant rate stepper motor to drive it.
I don't know of any commercially available versions.
Check out the AstroTrac TT320X Tracking Mount. Not low cost, but it works quite well, and is still fairly portable. I always wanted to get around to building something, but finally gave in to temptation when this came out.
