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iOptron SkyTracker Periodic Error
Another video showing the periodic error on one sample of the iOptron SkyTracker. I've measured this error in several ways, it always comes out to somewhere between 85 and 100 arc seconds peak-to-peak.
This image is of the region around the star Mintaka in the constellation of Orion (this star is at declination -17 minutes, much less than one degree from the celestial equator). The images that were used to create this video were captured with a 105mm Nikon lens on a Sony NEX-5N camera. Each of the sub-exposures was 5 seconds long and one image was captured every 10 seconds (or six images per minute).
The image has also been plate-solved and rotated to align with the celestial coordinates, so any left-to-right motion is in R.A. and any up-or-down motion is in Dec. Note how the stars move in parallel with the top and bottom of the frame. This suggests that I had pretty good polar alignment and that almost all of the motion was caused by tracking errors in the SkyTracker.
In any case, when I measured the periodic error I separated out the motions in R.A. and Dec. The 90 arc second error is for R.A. only, there was also a very small error on the declination, amounting to only a few arc seconds. This video covers about one and a half periods on the worm gear in the SkyTracker, so you see the range of motions over a time period that is just over ten minutes (at a 1:1 scale from the original images, or about 9.4 arc seconds per pixel).
iOptron SkyTracker Periodic Error
Another video showing the periodic error on one sample of the iOptron SkyTracker. I've measured this error in several ways, it always comes out to somewhere between 85 and 100 arc seconds peak-to-peak.
This image is of the region around the star Mintaka in the constellation of Orion (this star is at declination -17 minutes, much less than one degree from the celestial equator). The images that were used to create this video were captured with a 105mm Nikon lens on a Sony NEX-5N camera. Each of the sub-exposures was 5 seconds long and one image was captured every 10 seconds (or six images per minute).
The image has also been plate-solved and rotated to align with the celestial coordinates, so any left-to-right motion is in R.A. and any up-or-down motion is in Dec. Note how the stars move in parallel with the top and bottom of the frame. This suggests that I had pretty good polar alignment and that almost all of the motion was caused by tracking errors in the SkyTracker.
In any case, when I measured the periodic error I separated out the motions in R.A. and Dec. The 90 arc second error is for R.A. only, there was also a very small error on the declination, amounting to only a few arc seconds. This video covers about one and a half periods on the worm gear in the SkyTracker, so you see the range of motions over a time period that is just over ten minutes (at a 1:1 scale from the original images, or about 9.4 arc seconds per pixel).