LX600 StarLock Astrophotography Optimizations
Posted: 27 February 2016
I had originally planned to start construction of the POD Zenith Table (PZT) Friday morning, 26 February 2016. Unfortunately I had missed one essential tool in my previous reads of the construction manual: a 4' straight-edge. So I had to make a run to the hardware store (a 20 mile trip, one way). I now plan to start construction on Sunday, 28 February.
Open: Friday, 26 February 2016, 1807 MST
The first thing I did this session was to place a piece of red lens tape over the StarLock red LED status light. I had decided it was way too bright for my dark sky site.
Later in the session once it was dark I ended up using five layers of red lens tape to dim the LED sufficiently.
The main thing I wanted to accomplish this session would be to do all the StarLock enabled setups, with the goal of ultimately improving the StarLock autoguiding for DSO imaging. Before it got dark I tweaked the wedge base leveling to make it as horizontal as possible.
1817 MST: sunset. I would wait until closer to the end of Astronomical Twilight (1940 MST) before beginning the StarLock setups. 1905 MST: powered on the 12" LX600 telescope. 1918 MST: the Zodiacal Light was nicely visible. 1927 MST: viewed NGC2392 (Eskimo Nebula, planetary nebula), 102X. Excellent view. then viewed M31 (Andromeda Galaxy), followed by M81 and M82 galaxies, 102X. Some structure was visible in M82. 1935 MST: began StarLock optimizations.
The StarLock system uses a narrow field 80mm f/5 refractor telescope and a separate super wide-angle lens that automatically finds the selected object with high precision in conjunction with the AutoStar, locks on to a field star, and then automatically begins guiding. As I have experienced since first setting up my LX600 last week, StarLock works pretty well for visual use in both Alt/Az and Polar modes. But autoguiding has not been so good for astrophotography, as seen in one of the poorer examples of StarLock autoguiding before any optimization:
Note the stars and particularly the two faint satellite trails.
So, what are the StarLock setups that will optimize astrophotography? It does the following:
Polar Drift Alignment
Periodic Error Correction (Right Ascension)
Automatic Guiding Rate Calibration
Sync to attached camera field-of-view (FOV) center
I'll discuss each of these in the order performed.
The AutoStar handcontroller can show StarLock guiding information. This session, before starting any optimizations, the StarLock showed these values for guiding (arcseconds, which frequently changed) and "aggressiveness" (percentage):
Polar Drift Alignment
Although I had aligned the mount using the AutoStar One Star alignment, I thought it would be useful to drift align the mount. The StarLock can do very quick (supposedly) drift alignment by using a star in the south and a star in the east (just like with a manual drift alignment). But what is rather slick when using the StarLock is that it will tell you how many turns of the X-Wedge Azimuth and Latitude knobs to make and in what direction to polar align the mount.
When Drift Align was selected on the AutoStar the telescope was automatically slewed to a southern star near the Celestial Equator. Unfortunately, the selected star put the StarLock aimed at the observatory dome. The StarLock began "Searching, Calculating, Slewing" repeatedly but it never seemed to "lock on" to any star (which it couldn't, seen the StarLock cameras were obscured by the dome. After about 10 minutes I aborted the Drift Align. This problem will go away once I have the POD Zenith Table (PZT) installed as it allows the dome to be slide off of the observatory. I will try again once the PZT is installed.
Periodic Error Correction (RA)
I next began the StarLock Right Ascension Periodic Error Correction training. I slewed the telescope to the star Rigel and then selected RA PEC TRAIN from the AutoStar. One training cycle was supposed to take 7 minutes (according to the LX600 manual) and three cycles were suggested. When I started the first cycle the telescope slewed about 60° west and stopped. The AutoStar display showed "searching". Nothing seemed to be happening and after 17 minutes I aborted this training cycle. I decided to try again, this time using the star Procyon in the east. First I erased the PEC training data as I had no idea how good it was. This time when the RA PEC training cycle was started it worked. There was no 60° slew. The cycle took about 20 minutes (not 7) to complete, but it did complete. As Procyon was now close to the dome I slewed to the star Regulus and began the first PEC update. It completed in 25 minutes. The second update using Regulus also took 25 minutes. Although the entire RA PEC training process took much longer than expected, it seemed to finally be done. But was the RA PEC training good? That would be determined a little later. 2202 MST: the eastern sky was beginning to brighten from the rising waning gibbous Moon.
Automatic Guiding Rate Calibration (ARC)
The next step in the StarLock optimizations was to adjust the guiding "aggressiveness" for the current seeing conditions and imaging setup. I mounted the D7200 DSLR at prime focus + visual back + Lepus focal reducer. The telescope was still pointed at Regulus when I began the Automatic Guiding Rate Calibration by selecting it from the AutoStar. The process took 10 minutes. At the end, the Guide Rate had been changed the default value of 66% (shown earlier) to 32%, with the Guide values seen here:
The Guide Rates didn't seem to have been changed much following the Automatic Guiding Rate Calibration. But would autoguiding be improved? I was about to find out.
Sync to attached camera FOV center
After doing a focus test image on the star Regulus using the Astrozap focusing mask I did a GOTO Rigel and did the AutoStar SYNC with the star centered in the camera viewfinder. This does the usual AutoStar alignment sync but it also tells the StarLock what offset to use for the camera centering. By now the sky was getting brighter due to the rising Moon.
So, did the StarLock RA PEC training and ARC work to improve autoguiding? This is M42 (Orion Nebula), 30 seconds, ISO 3200, after all the setups were accomplished:
Compared to the earlier image of M42 I would say that autoguiding improved dramatically.
I will be doing further astrophotography tests on future sessions and will report how things are going.
2230 MST: removed the camera and focal reducer and viewed M42, 102X. Next, viewed Jupiter, 102X. Four moons and the Great Red Spot were visible. Then began closing up after a productive StarLock optimization session.
Close: Friday, 26 February 2016, 2246 MST
Session Length: 4h 39m|
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