RA Calibration Failure

[Tony Bigbee]

Hello,

I cannot obtain RA calibration and am using the latest PHD2 with a CGEM with an Orion Starshoot autoguider connected to the ST4 port of the mount.

Mechanical loading is either C11 or Skywatcher ESPRIT 100ED.  Both fail.   No or light wind.

The dist value never exceeds about 19 after 61 steps.

After looking through various diagnostic documents and postings, I've tried increasing the step size up to 2500msec and aggressiveness of 100.

I'm attaching scatter plots of the dx and dy for 2 calibration attempts.  They look strange;  one is for a step size of 1000msec, the other the 2500msec.

I've attached both a log and debug file.

Thanks for any advice.

Tony

[Andy Galasso]

Tony,

Sorry to hear you're having trouble calibrating.  It's not clear from the logs that PHD2's guide pulse commands are getting to the mount at all--I suspect they are not.  A good way to confirm this is to use the Manual Guide tool in PHD2 to see if guide pulses can move a guide star in each of the 4 directions (N/S/E/W).

You may also want to confirm that the guide rate in the mount is set to a value in the range 0.5x to 1.0x sidereal rate.  At 1.0x sidereal rate a 3 second guide pulse should move the guide star a distance of 45 arc-seconds, or about 7 pixels given your scale of 6.6 arc-sec per pixel.

Andy

[Andy Galasso]

I meant to also say that if you find that the Manual Guide tool cannot move the guide star, then you'll want to focus on the guide cable and connectors--try replacing the cable.

Andy

[Tony Bigbee]

Thank you for the suggestions, Andy.   I changed the mount guide rate to 99% and that didn't change anything, but once I swapped out the guide cable, calibration was able to complete.   I then saw the RA/Dec axis angles that are questionable alert repeatedly and guiding clearly wasn't happening.  I never did change the sidereal rate itself before I had to shut down.  I've attached the logs and screen shot.   Based on online research, the only remedies of which I'm aware are to do a better polar alignment and/or recalibrate.  Perhaps the log files will suggest other things to you.

Tony

[Andy Galasso]

Tony,

PHD2's warning that you had a bad calibration was valid: your the mount moves in the same direction regardless of whether PHD2 tells it to go North or South or East or West.  This is something you would see right away if you try the Manual Guide tool.  There's no point in trying to calibrate or to guide until you resolve that problem. I suggest using the Manual Guide tool to confirm that the guide commands issued by PHD2 can move the star in all 4 directions (N/S/E/W) before attempting to calibrate. Moving the guide star in all 4 directions is a requirement for guiding... if phd2 can't move the star it can't guide.

If using the On-camera (ST4) guide method is not working even after replacing the cable and checking the connectors, then you'll probably need to find another way for PHD2 to talk to the mount.  You could see if there is an INDI driver available for the mount and go that route and bypass the problematic ST4 connection altogether.

Andy

[Tony Bigbee]

Thank you for the suggestions, Andy.   The ST-$ cable/connection was problematic.

I switched to using ASCOM 6.3 and connecting to the mount through USB-> serial -> Nexstar hand controller.    But the mount is not responding to manual guide commands.   Using the small ASCOM GUI that pops up does result in the mount responding to N S E W commands, so I'm not sure why PHD2 cannot drive the mount.  I do see errors in the log, which I've attached.

I also tried the Indi drivers, but those aren't working in macOS, Ubuntu 16, or Windows.

best,

Tony

[Andy Galasso]

Hi Tony,

I see in the log that the manual guide tool was used 6 times to send a 2.5 second North guide command, then you exited PHD2.  There were no errors reported by ASCOM, so the ascom driver did accept those guide commands from PHD2.

I don't see anything in the log about any attempts to move in other directions-South, East, or West.

What appears to be lack of response to a northward or southward guide pulse is often a symptom of declination backlash.  6 x 2.5 seconds pulses should have been enough to take up any normal amount of backlash.

The ASCOM driver's GUI will move the scope at a much faster speed -- a slewing speed or a centering speed. PHD2's Manual Guide tool will move at guide rate, so the motion will be very slow.

One thing to do if you suspect backlash is to nudge the scope North using the ASCOM driver's GUI or the hand control before attempting to use the North guide pulse in PHD2.  The North nudge at a slewing rate clears the dec backlash.

I would recommend using the Manual guide tool to confirm all 4 directions of motion. Then, if that works, then you can proceed to calibration. Make sure you nudge north before starting calibration to take up the backlash.

Andy

[Tony Bigbee]

Thank you again for the diagnosis and recommendations, Andy.  I was able to successfully calibrate and guide on Windows 10 via ASCOM Celestron driver and going through USB->serial->NextStar handset.  I was unable to use/connect with the Indi drivers on Win10, macOS, or Ubuntu.  I had to flash the firmware in the NextStar handset for the ASCOM driver to see the CGEM telescope/mount--the firmware was about 1.5 years old and I was using the latest ASCOM platform 6.3 and Celestron drivers.  Bread crumb trail for others...

Attached are screenshots from the log viewer from a 22 minute guiding session and manual guiding.  I was able to capture 5 minute exposures with round stars on my QHY168C and Esprit 100ED OTA, but I'm requesting an assessment of the results.

Thank you.

Tony

[Brian Valente]

Hi Tony

Is your focal length on the telescope entered correctly in PHD at 2800mm? 

If i understand correctly you are using a skywatcher esprit 100ED, which is around 550mm 

Brian

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Brian Valente

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[Andy Galasso]

Hi Tony,

Glad to hear you were able to calibrate and guide with the Celestron ASCOM driver -- great progress.

We generally prefer to look at a full guide log and not screen-shots. However, from the screen-shots It looks like you have an incorrect guide scope focal length entered so the pixel-based numbers are not correctly converted to arc-seconds units.  You can fix this in the Guiding tab in the brain. Be sure to enter the focal length of the guide scope (which would be the same as the imaging scope if you are using an OAG.)

Andy

[Tony Bigbee]

Thanks for the detailed look, Brian.  You are right, the (new) OTA is 550 mm but I'm using an Orion SSAG for guiding and not OAG.   I was previously using a C11.

Best,

Tony

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[Tony Bigbee]

Ok, Andy, I appreciate the careful look and will fix the guide scope focal length for the next runs.   The log file is attached if it's worth something with the wrong focal length.

best,

Tony

[Tony Bigbee]

Correction - I'm using a Celestron 9x50 finder scope with an Orion SSAG... 

[Andy Galasso]

On Tue, Nov 28, 2017 at 1:53 AM, Tony Bigbee <tony....@gmail.com> wrote:

The log file is attached if it's worth something with the wrong focal length.

The log file looks pretty normal to me, I don't see any immediate issues there. I think you're ready to move on and take some nice guided images.

[Tony Bigbee]

I ran another session with the attached results. The seeing was forecast to be good to average.

The suggestions provided in this thread:

1.  Check guidescope focus.   Log star images.

I read up on the Star Profile and Target Displays and think I did better in this regard.  Adjusting focus on the guidescope seems to throw off the lock on a star, making this more difficult.  Perhaps user inexperience is the problem.

I did check the Enable diagnostic image logging and check For all Auto-select star frames, but no images were written to the log directory.

2.  Try PEC or PHD2 PPEC.

The session tonight was a first attempt at collecting enough data to use a third party PEC analysis tool.  Sections 6 and 7 in the log look adequate for that task.

3.  Try uni directional DEC 

Not tried yet.

The DEC pattern of staying on one side of the axis almost the entire time is a new pattern for me.  Cord issue?  The balance on the mount was done right before the session.

SPA - My first attempt to use this tool was an utter failure.  Most of the session occurred before attempting anything other than my usual manual polar alignment procedure.

Every time I clicked "Rotate," the selected star was immediately lost.   One thing I don't understand about the procedures is where to sequence the SPA.   The mount would not respond to SPA commands if I turned it on but did not do the initial alignment.  If did the alignment, then did a go to within 5 degrees of the pole (Polaris) and 90 degrees DEC, the mount returned to a configuration that did not match anything near the initial setup (counterweight down and the RA and DEC index marks aligned).   

I did run the Guiding Assistant, but after monkeying with the polar alignment, I'm not sure how reliable that information was.   

Reported backlash from the debug log:

Line 129396: 21:13:49.709 00.000 10896 BLT: Backlash amount is 15.28 px, 11889 ms

Thanks for the feedback to date and further suggestions.

Best,

Tony

[Tony Bigbee]

I found the auto select star frame files and posted them here:

https://drive.google.com/open?id=1PYEPW5yF17AzrFZljiyPqenRGyCSF-H5

[Brian Valente]

Hi Tony

good guide logs. the last calibration looked pretty good (except I don't know what are the ghosted calibration points, Andy/Bruce?)

i can see why there was a recommendation for PE correction - RA has a rather large periodic error.

i didn't see anywhere where you switched to PPEC algorithm for RA? you should definitely give that a try

Regarding DEC, there's a ton of backlash. so much that PHD appears to take a long long time to get it back on track. you might look into adjusting the dec backlash on your mount. 1500ms is pretty big. 

assuming you turned on auto adjust backlash, does it still report 1500ms now or another value? 

overall although the details look kind of ugly, according to your resolution, you are operating about 1/3 of a pixel for errors, so your stars should be nice and round?

Brian

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[Tony Bigbee]

Hello Brian,

I haven't tried PPEC yet, I was waiting to do the PEC work first, then try PPEC.

The largest stars are round, but the smaller stars are either a little elongated or have a some hot spots.

In my sessions from about a month ago using the same equipment but less experience with PHD2, I was able to obtain nice round stars with the 100ED with 10 minute exposures.

I've already had the CGEM hypertuned, so I don't know if I can do any better with the dec backlash.

Over about an hour period, PHD2 increased the backlash comp from 1500 to 3000 msec.

Best,

Tony

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[Tony Bigbee]

I inadvertently omitted that I am using a dark frame library in PHD2 for exposure times of 1 to 4 seconds.

[vVertigo]

Reading this post with great interest and hate to barge in. Have 10”lx200, modified super wedge, modified focuser with mirror lock, 400mm f5 guide scope with zwoasi290mc as AG(had only two days), canon 4ti thru 6.3 FR for main camera. Using old laptop winxp pro with bye, PHD2, latest ascom Driver’s from zwo website, use a pcmcia? Card that has 9pin serial .connection with phone connector on other for r232 scope. Sharpcap and Meade’s epoch2000 will communicate with scope ok, but last nites test only opened PhD. In PhD I selected the zwo camera, Meade classic under mount and both appeared connected. Once I center a star on screen, start looping, and then go to guiding star starts to move upward fairly quickly and numbers at bottom of screen show the ra/dec corrections(which were ridiculously high 20-30 pixels and higher) and in no time star was out of box. Next try I used phd manual controls to see if I could keep star in box but I didn’t see any indication it was moving any thing. NOW the Confession. Being so impatient to try out zwo camera I did not use my wedge, mounted altaz calibrated to two stars that were too close to each other(impatient and lazy, it was cold last nite remember) and so stars were not staying in for very long anyway, this was the worst setup I’ve ever done as for as tracking in 18 years I’ve had scope. So questions go:
1.The fact the PhD showed corrections for both ra/dec at bottom of screen, is that a sign it’s communicating with mount, or would it show this regardless.
2.I know it was probably rediculas for me to use sloppy setup to test this, and accounts for tracking above, but what I’m concerned with is when manual directions were tried there appeared to be no movement, star drifts north, so east/west movements should have been evident.
3.zwo is connected to laptop usb, And tried both with and without st4 connected to scope with no difference.
4. Is there a static way of testing phd2 output to telescope
I can’t see North Star at my home so we use the local gun club in country with beautiful dark full horizon, but you can imagine the setup like mind will be complex for polar alignment using PhD for first time, so I want to know for sure if the scope and PhD are working together before going to field.
If I resolve this will be good news, bad news is next would have to figure out the rest of that dang phd2 manual .
I have done film AS and digital AS with manual guiding in past, so know basics, just have trouble following forums when they use so many acronyms. Thanks vvertigo

[bw_msgboard]

Hi vVerigo. I can't make much of this but I can probably answer your
question about static testing. It's actually pretty hard to do this because
the angular movements of the gears are very tiny and happen very quickly.
If you remove the cover on the Dec drive system, you *might* be able to see
a tiny rotation of the worm if you get a helper to send a long-ish PHD2
manual N/S guide pulse - say 5 seconds long. If you can see that motion,
it's pretty likely the software is set up correctly and the driver/mount are
capable of handling pulse-guide commands. I'm assuming you haven't seen any
alert or error messages from PHD2 telling you the pulse guide commands
aren't working.

Bruce

[Bruce Waddington]

One other thing vVertigo - if you need to continue this discussion, please start a new thread.  What you're talking about is completely unrelated to Tony's situation.

Thanks,
Bruce

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[Ken Self]

Hi Tony

I had a look at your guide log and it looks to me like you have a very large polar alignment error. It is well in excess of 1 degree which is why the dec curve stays on one side.

Now with that much PA error, if you have star aligned your mount and try using SPA it will not work well in auto mode. In auto mode SPA issues goto commands which should only move in RA but the mount controller changes those to correct for the misalignment and includes some dec movement which messes up the calculations.

What you should do is to start with the polar drift tool which will quickly get you to a much better polar alignment - say 10minutes. Then you can switch to either SPA or drift alignment to get it to 5 minutes or less. If you use SPA its best to clear any alignment points first. If it still isn't behaving you can try manual mode or drift alignment.

For your PEC analysis you need to disable guiding before starting the trace. You've got guiding on so the PE is being corrected out.

[Tony Bigbee]

Ken - Thank you, this is the advice for which I was hoping.

Tony