Thursday, September 07, 2017

The Barndoor Tracker Revisited

Well, I got a chance to put the Barndoor Tracker to use this summer. On August 21st, I was privileged to observe the Great American Eclipse from Glenrock, WY. The weather was sparkling, except for some high, wispy clouds that showed up just in advance of the eclipse and continued to grow a bit right after. However, photographic opportunity was perfect and the eclipse occurred right on schedule.

In advance of the eclipse, I did a considerable amount of testing and work to get the tracker properly aligned to track the sun. I learned a lot about both astrophotography and the tracker. One thing is that the tracker has got a bobble to it. It tracked ok but not perfectly. The sun stayed in frame but it would move a bit from one picture to the next. I was taking pictures every two minutes and the sun would move one way and then the other. I think that there were two things that contributed to this. One was that the geometry is too complex. I plan to rebuild it this winter to align the pivot points with the lead screw. This will get rid of some of the calculations needed and also will make it easier to get the pivot points straight. That leads to the other possible problem, that at least one of the pivot points is not straight, which makes the door open at an inconstant rate.

The other thing I learned about the tracker was how to get it aligned. I had to do it the night before by sighting on the North Star (Polaris) with my camera attached to the tripod and shooting a timed exposure of about 30 second. Then I zoomed in on the image and adjusted the tripod to get the star to align perfectly with the center of the image. When this was correct, and the tripod was completely locked down against movement, I retired and, in the morning, attached the tracker to the tripod without disturbing it. After this, it tracked quite accurately, except for the aforementioned wobble.

So the other day I was at the Fry’s here in Wilsonville, Oregon, where we are visiting now that the eclipse is memory and photos, and I bought a Raspberry Pi. I guess I will be exploring this next and figuring out what I can do with it. Fun.



Jamey said...

Great eclipse photo Geoff! (What camera/lens did you use to take your photos?) Have you used your tracker to take any nighttime astrophotos? I'm planning to build my own arduino/barn door tracker in the next few weeks, and your flowchart for the software will be very helpful.

Geoff said...

Jamey, thanks for the comment. I used a Nikon D5600 with a 300mm lens (55-300 zoom). This picture is an HDR composite of 11 photos. I have not used it for night photography yet.