Since it had been two weeks since my last imaging opportunity, imaging conditions (transparency and seeing) were marginal, and the Moon would be rising before the session ended, my objectives were to get in a practice run, try a new PHD2 Ra guiding algorithm, and capture some test images. For practice and test images, wanted to walk through PHD and NINA start up and start an imaging run on the Flame/Horsehead complex. The new Ra guiding algorithm that I wanted to try was Predictive PEC to see if it would improve Ra guiding.
When I went out to polar align, the temperature was in the upper 30s, RH was about 60%, and there was an occasional light breeze, which was projected in the forecast.
After polar aligning, I stepped right into calibration. A slight issue here is that I had deleted the old PHD equipment profile and established another one. I did not re-do the Darks library, because I thought that the old one was still valid. Just to be sure that everything is synched, I will establish another new profile and re-do the Darks library.
I got a great looking calibration graph, so I moved on to GA. I let it run for over three minutes before stopping it. I was surprised by the Dec backlash measurement, which was below 700ms, and I got a great looking backlash graph. I attribute this result to the one-piece worm block that permits much easier backlash adjustments.
From there I stepped into guiding, and let it run while I had dinner. Maybe 40 minutes. From memory, RMS numbers were about .75” for Ra and .55” for Dec. Total was less than 1”, which even with marginal seeing favorably compares to my image scale of 1.11″.
As for improved Ra guiding, the bad seeing made it difficult to say how much of a difference P-PEC actually made. My Dec was worse and I attribute that to bad seeing, and Ra was slightly improved, but better seeing, it seems, could have shown more improvement. Ra and Dec RMS values were closer to being equal and stars were rounder.
At 2025 I began an image run on Flame/Horsehead of 45 frames per filter, 60s per frame.
I concluded the session at 2250. The temperature was 25 degrees and RH was 60%. Although the forecast had projected the winds to die down by then, there was still a pretty good breeze. There was no frost or dew on anything.
Tonight was a good use of a marginal night to try out a new setting, and get in a practice session.
Guide Log Analysis
I have reviewed my guide logs and have decided to do nothing at this point as a result of what I see in the logs, because I think that seeing was the overwhelming factor in the results. I am basing my conclusions on Section 1 (Calibration) and sections 9, 10 and 11, which were my 46-minute RG and B runs. I didn’t write anything down, so I don’t know what the other Sections reflect.
Although seeing was sub-par. My RMS numbers were pretty decent. While I was looking for less than 1.11” RMS to beat my image scale, I was getting no worse than 1.02. Ra and Dec RMS were about .85” and .50” respectively. The improved difference between Ra and Dec RMS is probably a result of using P-PEC.
In Dec I see a pattern of guiding spikes that seem to be higher than warranted for amount that the star had departed the center line. I think that this was bad seeing, and perhaps sub-optimal Dec guiding settings.
I do see an interesting long-period oscillation in Ra that was not there before. I showed you the 240s worm period oscillation in my log charts from the 29th. They are present in last night’s log. You can easily see the 240s PE oscillation by right clicking in the Section 9 graph, and selecting Analyze selected, raw Ra. You can see 11 or 12 240s oscillations, but notice how the trend of the oscillations decreases, increases, and decreases again. If you click on the Frequency Analysis button, you can see the 240s peak that we were seeing before, but there is another peak out near 2000s.
Just guessing here, but I think that this is related to the use of P-PEC. I noted last night that P-PEC had auto selected a period of 239.70S, which is a little short of the G11’s actual period of 240s. I wonder if this is causing the 2000s cycle. I may try manually entering the period as 240 next time to see if that makes a difference. I am not horribly concerned about this as the Ra RMS was better.