Re: DEC Tracking test


Ray Gralak
 

Thanks Craig for the feedback! I am glad your initial tests went well.

We'll definitely discuss your suggestions. Of note, NINA will soon have a feature that can invoke APPM to auto-map a couple rows of data around each target before imaging that target. Would that satisfy your item #1?

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Wednesday, September 1, 2021 12:18 PM
To: main@ap-gto.groups.io
Subject: [ap-gto] DEC Tracking test

I have been a major critic of APCC over the last several years due to its poor tracking performance on my 16"
RC w/1600AE mount and plate scale of 0.57 arcsec/pixel. So it was with great enthusiasm to finally get a
chance to try out the new DEC arc tracking feature in APCC. For my photometry research program it is
required that the mount track on the same pixel over a 6 hour DEC arc run. I don't use an autoguider because
of all the technical issues and instead wrote a software program called ATrack which controls the mount
precisely using science image plate solving in real time to make corrections to the mount tracking. This has
been successful and achieves the goal of 1 pixel over 6 hours without an autoguider.

So last night I setup a DEC arc centered of -30 DEC (I am in southern hemisphere), east sky only using 3 DEC
arcs with 1 degree spacing: -31, -30 and -29. The RA spacing was set at 5 degrees and the arc ran from -3 HA
to 0 HA. This resulted in 9 points on each arc for a total of 27 points. APPM collected the data which took
only a few minutes and built a model based on these parameters.

I then pointed the mount at -1.5 HA and -30 DEC and recorded 20 images each of 60 seconds. No autoguider
was used and ATrack was used to measure the drift and image shift numbers without doing any corrections.

The results were spectacular. ATrack reported an inter-image drift of less than an arcsecond, typically 0.2
arcseconds across all 20 images. Over the 20 minutes or so of testing the image drift was no more than a
couple of arcseconds with the final image being less than an arcsecond from the first image in the sequence.
Residual tracking errors in each image combine to produce an image shift over the entire run but ATrack can
easily correct for this by re-centering the next image. This is done by adding a slight bias in RA and DEC to
the tracking motors for a period of time, similar to what an autoguider would do when using pulse guiding
corrections.

More testing is needed but I would like to request two features:
1. A tab on APPM titled "DEC ARC models" in which you define your DEC arc. For example, a DEC arc
would be defined as centered on -30 15 27 and a spacing of 1 degree. This would result in a APPM model of
three arcs, the center arc, and an arc on either side separated by 1 degree. In addition, the RA spacing could
be specified to define the number of points on each arc. The defaults for this would be: DEC position would
be current mount DEC. DEC spacing would be 1 degree. RA spacing would be 5 degrees. And a checkbox
for East or West or both. A name for the arc would also be good. I believe this would make it easier and
faster to create DEC arcs.
2. APPM is used to create multiple DEC arcs, one for each object being imaged. Then when the mount is
slewed to an object, APCC looks for the DEC arc that most closely matches the object DEC and loads it.
That way the user does not have to manually do this.

In any case, well done Ray for providing us with an excellent new tracking feature and all the hard work Ray
and the AP team have put into this. This really advances the software capability of APCC and shows how
good the AP mounts and software can perform.

Craig
Crystal Lake Observatory
New Zealand

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