Equipment Tuning

Earlier today I was thinking that I could work through some guiding stuff that I had read about, and then pretty quickly and move on to imaging. Seeing threatening weather when I went out, I was pretty sure that I would be working on guiding only. That’s the way the night turned out.

Set up and start up went flawlessly, as it does lately. I powered up at sunset (2030), had software up and connected to equipment and was waiting for Polaris to appear in the Polemaster display by 2050. I had Polaris at 2108, and was able to quickly polar align. It felt pretty solid.

Checked focus, and it was good enough for my purposes, so I moved on to calibration.

Calibration passed without error. Orthogonality looked good, and I had a slight squiggle in the dec leg. I’ll take that too.

I then went to Drift Alignment. I worked with the tool from about 2120 until I shut down after being clouded out at 2245. I did not have much success at all.

I should add that I adopted a few points from Rista, but otherwise elected to use the bolt adjustments to move the trend line to zero using the az and alt bolts. The points that I adopted from Rista, which I need to add to my workplan, was to star align, slew to CE-Meridian (not just close), and set looping to 1s. I also added a Jim-step, which is to periodically slew back to 0,0 after the mount has run westward for more than a few degrees. All of this was easy to execute.

First, it felt like the Dec (red) trend line was not responding to my bolt adjustments, no matter what I did. I would call it non-sensical much in the same way that yours appeared when you were here last. At two points, I got it the trend line to move upward until the az error was about 8’ and then instead of the line going to or past zero with additional adjustment in the same direction, it went back down. I was really feeling like I was missing something big.

I was also feeling like the Az error was not going to get any closer until until the Alt adjustment was closer. Thinking about it right now, that seems pure nonsense. I now have a theory that when I see an 8’ error when I am making az adjustments, that number just applies to the az error, and vice versa for alt adjustments. If this is correct, then I surmise that you need to be in the GA tool to see the overall PAE.

After this happened the second time, I struggled to get the az error back to 8’ again, and then I switched over to alt adjustments, and had a similar nonsensical experience. I got the alt error as small as I could and gave az adjustments another try, and was getting little to no response to my adjustments, even when I was making big ones.

Then the clouds came in, and I shut down. As is my habit, I reached for the scope put the counterweight bar and scope in horizontal orientations manually. Both the Dec and Ra clutch were extraordinarily loose, and the mount could be turned with very little force. I think that the inertia of the scope and counterweights overcame any friction (well-lubed mount, so almost zero friction) in both axes, and therefore the scope did not move when I made an adjustment.

I have a step in my work plan, which I followed tonight, to check the clutches and set them properly – moderately firm. In fact my step says to make sure that they are not so tight that they cause stiction, which I found to be a problem months ago, and to make sure that they are not so loose that I lose my star alignment with a small bump.

I accept too loose clutches as the reason for the difficulty, but peeling the onion back another layer, I ask why were they too loose after I had adjusted them? It was still pretty warm when I went out, maybe 88 degrees. I think that the mount cooling down is probably the answer, so perhaps another gotcha that I need to be on the lookout for.

At this point I am resolved to keep working with the drift alignment until I can get a 1’ -ish overall PAE as measured in the guiding tool. An then, I have a couple of guiding adjustments that I want to try. Then I will move on to imaging. That will be my objective tomorrow night.

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