My objectives were to check Dec backlash after adjusting it last week, test the autofocuser position consistency, and get some experience with the IR temp gun and dew point indicator. I also wanted to take a south horizon cell phone image for comparison to my backyard horizon rendering in Stellarium, and gain some experience with the smartphone camera doing wide-field night sky shots. Progress was made on all objectives.
An overall observation
As tonight’s work was almost entirely dedicated to testing for the purpose of making improvements, I realized that since April I have been taking an informal Lean Six-Sigma approach to process improvement to get consistent and high-quality imaging results. Thank you NGA for the LSS class!
Also, as I am getting better and documenting my sessions, I am getting better at noticing more subtle connections. There is an example of this in the PHD guiding section where I noticed bi-directional Dec guiding adjustments and how that might related to the inability to measure backlash
I have also noticed that the items that I fix, with the exception of RDT, stay fixed. My set up and automation is complex, but it does feel that I am making progress toward where I want to be.
The Astronomer
I was very tired at the outset, and got a little chilly as the night wore on. I think that a chair nap would have helped, and I could have done that while clouds were rolling through. Chair naps seems to be a lesson that I refuse to learn. I was in bed by 0215. I tried to get up when Lisa did at 0700, but ended up going back to sleep until 0950.
The Clouds
The first cloud bank rolled in at 2200, but by then I had completed polar alignment and calibration, and had started on a Guiding Assistant run. I went inside and came back out 45 minutes later, and the clouds were gone. I completed a Guiding Assistant run, and started on the autofocuser/filter test. Another bank of clouds came through, but I stuck with the test and got enough information to reach a conclusion. The sky was completely clear when I ended the session at 0130.
Equipment
Setup, power up, and start up went extremely well. The equipment did everything that I asked of it, but testing revealed that I need to make some adjustments in what I am asking of it.
PHD2/Backlash test
The backlash test is a part of my usual PHD2 start up, and is done in calibration and GA tool.
In calibration, the orthogonality error was 6.7 degrees and the graph had a slight S-curve for the Dec leg, probably due to backlash. The orthogonality error was about the same as last time,, but the results graph looked a lot better than before. The orthogonality error makes me wonder if there is another problem causing that error, but for the time being, I want to get backlash squared away before chasing that problem.
In the GA tool, I was able to see that the polar alignment error was 2.7’. The backlash measurement failed (like last time) because PHD could not detect a consistent south response., so I still do not have a measurement in ms. The results graph looks a lot better. Before, the leg that was supposed to slope downward at 45 degrees was horizontal, which is consistent with no consistent south response. This time, there was some downward curvature, which is a slight improvement. Thinking about this today, the Dec drift was southward and the slope was pretty steep. Maybe tightening up the worm gear adjustment will help, but maybe I should try using PHD Drift Alignment Tool to decrease the Dec drift.
While monitoring the guiding graph after the GA run, I noticed that PHD2 was issuing both north and south guiding nudges. While monitoring the graph during the GA run, I noticed that the Dec drift was south. As this is a function of polar alignment error the Dec drift can be in only one direction, and since the drift is south, the Dec
guide commands should only be northward.
After the GA run, the Ra/Dec/Tot guiding RMS was 1.37’/.57’/1.59”, which is worse than I have been getting lately. After changing the guiding algorithm from Auto to North Only, the Ra/Dec/Tot RMS improved to .78’/.49’/.90’. This is a dramatic improvement, but thinking about it as I write this up, it seems that going to North Only would have affected the Dec RMS, but it was the Ra (and total RMS) that improved dramatically.
To-do Items related to Guiding:
Tighten up the worm gear adjustment a little more and see what happens next time.
Add a DSO Workplan Step to check for N and S guiding on the Dec axis, and to reduce Dec drift with the PHD2 Drift Alignment Tool
Investigate Ra guiding improvement as a result of going to North only guiding on Dec axis
AutoFocus/Filter Test
The reason for designing this test was to investigate the appearance of a highly bloated guide star in PHD2 well into my last few sessions. My hypothesis was: Since the main camera and the guide camera move in unison as the focuser is racked in or out, maybe the focus position from an autofocus run was different from filter to filter, or maybe autofocus was not consistent for the same filter.
The test that I designed to evaluate this was to set up a sequence in NINA that would autofocus on a filter, do a 10s exposure on that filter, and repeat for the next filter. After cycling through RG&B, the RGB sequence was to repeat RGB ten times.
My expectation was that every time the same filter came around, the autofocus position for that filter would be very close the same for each measurement, an maybe the autofocus positions for the RG and B filters would all be close enough to use one focus position for all three filters.
What I found was that there was no consistency in focuser position for any filter. The results could very by 20 steps for the same filter. This could account for star bloat in PHD2.
I have found a CN post that addresses settings that will improve this. I will read, adjust the settings, and re-run this test.
Night Sky Imaging with the Smart Phone
I mounted the smart phone on a regular camera tripod using the $10 adapter that I bought for the backyard horizon panorama. Some exposures appeared to be a single image, whereas other exposures clouds could be seen moving across the FoV. Not sure why the difference, but worth investigating.
The moon tracked higher across the trees than Stellarium had projected, which seem so suggest that something needs to be adjusted. It could be that my accuracy expectations are completely unrealistic.
I would like to experiment with the smartphone and the adapter on the wind up star tracker that I used for Three Comets.
Objective Lens Dew Monitoring
I set the dew controller to 33% at sunset, and left it there for the rest of the night, and periodically monitored the air temperature, lens temperature, dew point, and relative humidity. I also noted if there was dew on surfaces (like my metal table) or on the lens. Ideally, I would have had a control lens that was unheated so that I could really know if my heating approach was successful. Also, this is just one night’s observations with just one telescope.
One difficulty was the impact on the imaging sequence. I had to stop the sequence before pointing a laser dot down the front of the telescope. It seemed worth it time impact. I expect that as I gain enough experience that at some point I may no longer need to monitor the lens temperature
Here are the raw numbers:
| (d) | (d) | (d) | (%) | (% pwr) | (y/n) | (y/n) | |
| Time | AirTemp | LensTemp | DewPoint | RH | DewCont | SurfDew | LensDew |
| 2030 | 70.8 | 75.2 | 62.8 | 79.2 | 0 | N | N |
| 2105 | 67.6 | 72.5 | 63.3 | 87.1 | 33 | N | N |
| 2204 | 67.0 | 71.6 | 64.0 | 90.9 | 33 | N | N |
| 2300 | 63.5 | 69.0 | 62.8 | 97.5 | 33 | Y | N |
| 2330 | 63.1 | 68.1 | 62.1 | 97.2 | 33 | Y | N |
| 0030 | 63.1 | 67.3 | 62.4 | 97.1 | 33 | Y | N |
| 0130 | 61.9 | 66.7 | 61.1 | 98.5 | 33 | Y | N |
Looking at the data, I have made some observations
Dew did not appear on other surfaces until the RH jumped up into the high 90s.
The lens temperature consistently stayed about 5 degrees warmer than the air temp.
The air temperature and the dew point in the backyard weather station began running parallel at 2300, converged at midnight and remained converged for the balance of the night. This is consistent with the observations that I recorded.
From these observations I have drawn some conclusions.
33% dew controller heat kept the dew off the scope all night, but future monitoring is necessary
Maybe the RH% is a good metric to monitor for knowing when to crank up the controller.
Todo Item: Add wind speed and direction to the observations that I collect.
Where to go from here.
The Astrosphereic forecast for tonight is for better cloud cover, transparency and seeing than last night, but the nearly Full Moon dominates the sky. It is still a good night to get some useful work done, so I am planning to work at the scope again tonight. I think that my prep time today will be best spent on the updates to my work plan that could give me a better dec backlash result, so I want to try this before I actually adjust the backlash. I also want to read and tweak AF settings before I repeat the filter/autofocus test.
I will work off of last night’s polar alignment, I and can probably get through the PHD start up calibration and GA run pretty quickly. Once that is done, I can load and initiate the NINA sequence, which takes a quite a while to complete, but it runs autonomously. I am available to work with you and the CG5 if you want to come over. I can monitor both scopes for dew.