The Great Hercules Cluster (M13) and Equipment Tuning

The sky cleared off at about 1800 last night just as Astrospheric had forecast that it would, so I went out and set up for DSO imaging before dinner. My objectives were to check today’s backlash adjustment, and to test autofocus. I also did a test imaging run on M13.

The NP101 was on the G11. I added the ASI6200 and connected the power.

The temperature when I went out at 2050 to power up, polar align and set my initial focus was 62F, and there was no discernable surface breeze. The Astrospheric forcast for transparency was average, dropping to below average by 0100. The seeing forcast for the night started at below average, improving to average by 0300.

After polar alignment and calibration, I slewed to a star field near Arcturus to check autoguiding. The RMS error numbers looked a little worse than the night before, but sill not too bad: Ra RMS was .78”, Dec RMS was .58” and tot RMS was .99”. Ra backlash was so bad that the Guiding Assistant tool could not measure it.

Next I worked on autofocus. After making sure that the clutch was engaged, I got a good graph on the first try. I tweaked the parameters a bit before sticking with parameters used for the third run.

I did two M13 test runs. The first was a 24-minute run with PHD operating separately from NINA (both were running), and the second with a 30-minute run with NINA controlling PHD. I compared the PHD logs for the two runs to star eccentricity analysis of the images in PixInisght. The PHD chart for the first run looks horrible. The Ra, Dec and total RMS errors were 1,07”, .69” and 1.27”, respectively. The star eccentricity for the images from this run showed .75 to .95, which is pretty bad. Visual inspection of the images shows elongation of the stars that is consistent with the Ra RMS error being larger than the Dec RMS error by almost 2x. The PHD chart for the second run looks much better with Ra, Dec and Total RMS errors of .76”, .53”, and .93”, respectively. The star eccentricity chart for these images shows .45 to .6, and visual inspection reveals round stars. The eccentricity seems consistent with the RMS numbers.

Autoguiding seems to work best as a stand alone app (without NINA controlling the mount), or with NINA controlling PHD. It does not seem to work well when PHD and NINA are running separately and at the same time, but not connected to one another. I need to work on the backlash adjustment to get back to at least what I had two nights ago.

Wrapping up at 2345, I noticed that there was dew on the grass but not on the equipment. This was the first dew that I have noticed this year. The temperature was 57F, and I noticed that the temperature and dewpoint plots on my home weather station had nearly converged, and perhaps were just beginning to run parallel to one another with the dewpoint being about 4 degrees less than the temperature. Last summer I surmized that dew begins to form when the two plots begin to run parallel, so I will watch for the coorelation between the plots and dew forming this summer.

I have posted a single test frame from the first run. The image is highly cropped, and it is stretched. Noise (even when zoomed in) doesn’t look bad. I had previously thought of objects like M13 as quite large, but it looks very lost in the uncropped ASI6200 full frame. I checked it out in Stellarium and found the following:

M13 is about 20’ in diameter.

The Meade/6200 fov dimensions are 50’ x 33’

The NP101/6200 fov dimensions are 3d 49’ x 2d 33’, or 7x larger than with the Meade.

Using the Meade/6200 combination, M13 fills the frame much like the cropped image from the NP101/6200 combination that I posted. I am sure that the Meade with its longer focal length and larger aperature will produce a more pleasing, higher resolution image that I can get with the NP101.


The Meade is better for 20’ and smaller objects like clusters and smaller galaxies

The NP101 is better for large objects like M45, M32 and M42, and extended objects like North America Nebula, Cygnus Star Cloud and Markarian’s Chain.

Decision: Keep pressing forward with NP101 DSO imaging to improve my skills through the summer, as this is the best learning platform, and some of the larger objects are coming up. I will not stop working with the NP101, but will start to include some DSO imaging with the Meade as fall approaches.

The Good:

Autofocus worked perfectly…schweeeet!!!

I think that I am closing in on how to adjust backlash.

Setup workflow has smoothed out very nicely. If not for a Remote Desktop drop, my outside time to power up, polar align, and get to initial focus would have been twenty minutes. After going inside, I did not return to the scope until the end of the session.

Working inside of NINA is getting smoother.

I am feeling really good about being ready for the farm when the time comes. There are workarounds for all of the problems that I am experiencing, but I will have a more enjoyable dark site session if I can get some things fixed. A dress rehearsal or two will be very helpful.

The Bad:

Backlash is worse after yesterday’s adjustment. Backlash was so bad that PHD could not measure it. I think that I am now better prepared to fix this.

The M13 imaging data (image metrics and autoguiding metrics) do not look great.

The Ugly: I am getting frequent Remote Desktop drops and periods of lag. Sometime it works perfectly for extended periods. It is really great when it works. I want to carry everything to the curb when it doesn’t.

Immediate plans:

Next session will be a dress rehearsal that will include plate solving, autofocus, autoguiding, full compliment of LRGB filters, and flat calibration frames at the end.

I will continue to work on:

Backlash. I need a cloudless day so that I can see sunspots. When I last adjusted before yesterday, I could see sunspots continue to move for about 3s after an east slew. It was cloudy and I could not measure the backlash duration after yesterday’s adjustment. Even so, it felt pretty tight. I will measure the current backlash  duration before adjusting it. It seems that I am get pretty good guiding with 3s backlash, but I’d like to tighten that up just a little bit.

Remote desktop drops. This is very frustrating!! I’ll test to see if I get drops with the nano router or with hard wired Ethernet connection. I am pretty sure that Ethernet will be a workable fallback position until I get this fixed.

M13 - 2022-05-11 03:25 UTC - Test

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