My objective tonight was a pre-Farm practice session so that I might have the opportunity to discover and correct problems before going to a dark sky site.


I changed my target from Crescent Nebula to Sadr, which is a star located at the intersection of Cygnus’ wings and fuselage (sic). It is situated in an interesting and dense Milky Way star field. It lies less than a sensor frame to the east of Crescent Nebula. I may do a multi night collection on this target, but I think that ultimately it will be a better narrowband target.


I had taken the TV of off the mount right after the last session so that I could attend to a todo list item, which I got taken care of yesterday. I started setting up at 1935. After putting the scope back on the mount, I added the camera, and made power and data connections. Initial power up was complete by 1955, and I was waiting for the sky to get dark enough to polar align. All activities here went smoothly.

When I returned to the scope at 2115, the temperature was 70F and the dew point was 68F. There was no discernable surface wind, and there was some dew on metal surfaces. Later, a slight breeze picked up and the dew went away. The sky was completely clear. The forecast was for the temp and dew point to stay separated by about 10F all night. Tracking together but at a greater separation than usual was new to me, so I didn’t know if that would mean a dewy night. Astrospheric forecasted 0% cloud cover, above average transparency, and below average seeing.

The sky was dark enough for me to acquire Polaris at 2122, and I was able to complete polar alignment in one iteration by 2227. Polaris was just inside of the alignment circle at the end of the procedure, and it needed very slight adjustments in El and Az to center it up.

I began the initial focus at 2127. The focus position was pretty good when I checked with the Bahtinov mask as the position was not perturbed from the previous session. I initiated an auto focus run, that showed a R squared value of slightly less than 1 (I am used to getting perfect 1s lately) and finished up by focusing the guide camera at 2147.

PHD2 calibration began at 2147, and it went smoothly. The orthogonality was off by only 6.5 degrees, and the chart looked pretty good. Initial guiding was Ra/Dec/Tot of .94”/.38”/1.03”.

The Guiding Assistant tool ran from 2154 to 2207. It found that the polar alignment error was only 1.6’ – the best I’ve seen yet. The backlash measurement failed because the mount never established consistent south moves. The chart was horrible. The south leg of the chart was horizontal instead of the nominal 45d downward slope. Guiding Ra/Dec/Tot afterward were 1.03”/.68”/1.19”

With the minor exception of the R squared < 1, everything up to this point was as good as the results that I have been getting lately.

At 2207, I started target acquisition, using the NINA manual rotator. I don’t think that it will work with my setup because the sensor and OAG cannot rotate independently. The only rotatable point is the focuser body, and since it is forward of the OAG, the rotation ruined the calibration. After manually rotating to get approximately the 45 degrees that I wanted, I initiated another calibration run. The dec leg of the chart was extremely bowed away from the ideal path. Guiding Ra/Dec/Tot were .66”/.79”/1.08”, so I accepted the calibration and moved on by slewing to the target. Since Sadr does not have an image in the framing data base, I elected to slew to it using coordinates in the Gemini hand controller. I had Stellarium connected, and in retrospect I wish that I had used it to command the slew to the target because that would have been easier. Sadr landed exactly where I wanted it within the frame.


The imaging sequence was: slew to target, center target, start guiding, start imaging (RG&B: 20 x 120s, L: 140 x 60s)

I initiated the imaging run at 2233, just four minutes before end of astronomical twilight. The plate solver needed a slight adjustment and the autofocus ran flawlessly. I noticed as the first image started that I had set the exposure duration to 480s, the number that I was using for farm planning purposes. I aborted the run, and reset the exposure duration to 120s, which is more appropriate for the R filter in the local Bortle 6 sky. I had to reinitiate the exposure sequence which drove a time impact of another plate solve and autofocus. The first image was downloaded by 2250, and although it was a single roughly stretched image, it looked pretty interesting. The Ra/Dec/Tot guiding were .94”/.68”/.99”

0240 Checkup: Temp was 61F and dew point was 51F. There was no dew on metal surfaces. Unable to re-establish RDT except through Ethernet cable. Sadr was nearly on the meridian, so I stopped the sequence and initiated a meridian flip with the hand controller. I used the hand controller and Ra/Dec coordinates to return to Sadr. NINA executed a plate solve and autofocus without difficulty after I resumed the sequence.  I think that I am ready to implement flips in NINA. Guide star FWHM had bloated to 7. I need to study this more closely to determine what is going on. Guiding was pretty good after the flip. Ra/Dec/Tot were .54”/.66”/.85”. The L sequence line was executing. Subs 57 through 61 could have been affected by the flip. Sequence ends at 0420.

0415 Checkup:  Although the image session was set for 140 L subs, I cut it off at 100 at 0425. Guiding Ra/Dec/Tot were .74”/.43”/.86”. I noticed that post-dither PHD settle time seemed long, but I could not find a setting in PHD or NINA. Temp and dew point were 60F and 50F, and there was no dew on metal surfaces. There was no discernable surface breeze. The sky was completely clear.


Started Flats capture of 30 subs/filter at 0425 and finished at 0505 (25 minutes). Exposures ranged from 3 to 9s. I changed each filter’s max and min exposures to 1s and 3s respectively to shorten them even more next time. I think that I can force that range for all filters with brightness adjustments and removing card stock sheets if needed.

Dark Flats capture of 50 subs/filter began at 0506 and lasted until 0550 (44 minutes). It was getting pretty light by then so there is some worry about light leak.

Wrap up

My attempt to use the rotator cost some time, but that’s ok. I was really intrigued by the possibility of being able to get the exact same sensor rotation when collecting data on the same target over multiple nights, and I was disappointed that it doesn’t appear possible on my equipment, but I do want to explore other ways to handle rotation. Thinking about it afterward, it seems easy enough to rotate the camera to where I want it when I install the camera. I can use a piece of tape to mark the rotational alignment if I plan to collect more data on that target on another night.

After keeping my head in the work plan up to Polar alignment, I got away from it once I reached that point. Having the discipline checking my activities against the plan would have avoided the Stellarium error. It is not as easy to see the plan in the dark, but it is not that hard either. Also, I wasn’t careful enough when adjusting the exposure duration numbers that I plan to use at the farm for use at home.

Later auto focus runs had better R squared numbers. Focus positions sometimes were consistent and sometimes changed a pretty good bit. This is something that I will monitor.

RDT connects easily, but the connection is periodically interrupted. Reconnect happened quickly and without trouble through initiation of the image sequence. Checkups that came later checks required the Ethernet cable.

The Dark Flats were ruined by light leaks, but I can recover by reshooting these in the dark box. Going forward it will be better to begin the Dark Flats earlier/while it is darker. I must begin the Flats earlier than I did this morning (0425), and I need to limit them to 5s so that both the Flats and Flat Darks finish while it is still dark. Also, I left the Flat light panel on top of the telescope, switched off, when covering it for the Dark Flats instead of screwing the cover back on.

Todo List

  • Research workarounds for rotating the ASI6200 independently from the larger/M66-threaded OAG.
  • Investigate increase in guiding FWHM
  • Consider automating meridian flips in NINA
  • Monitor guide star FWHM bloat
  • Test for autofocus offsets across the LRGB filter set.
  • Inspect L frames #57 through #61
  • Process and archive data
  • Check chair rivets
  • Look for post-dither settle time setting.
  • Re-shoot Dark Flats
  • Update the work plan to reflect getting an earlier start on Flats/Dark Flats, shorter sub exposures, and screwing on the front cover.
Sadr in Cygnus - 2022-06-28

Leave a Reply