Sruggling with Guiding since adding OAG

[Tom Johnson]

So I have a Celestron Nexstar 8se on a Skywatcher EQM-35 Pro. Been using for a couple of years with an external guide scope and guiding was ok with the .63 reducer but not so great without reducer due longer focal length. Thought I would get the ZWO OAG and see if I could improve my guiding a bit, but so far not the case. No matter what I do when I calibrate I get a message about RA and Dec angle being questionable, and when I look they are either both in the same direction or close to 180 degrees apart in exact opposite directions rather than perpendicular. Not even sure how that is possible. I use polemaster to polar align, and even with the questionable guiding or no guiding I'm still able to keep about half my subs so don't think it is a polar alignment issue. My guide camera is ZWO asi290mm mini with pixel size of 2.9 and my focal length with .63 reducer is 1298, but per astometry.net it is actually closer to 1198 so have those values entered. Have tried running Guiding assistant, but that hasn't changed anything either. Any advice is appreciated.

 Here's a link to my latest PHD2 log file, https://openphdguiding.org/logs/dl/PHD2_logs_GPNR.zip

[Brian Valente]

Hi Tom

I think you may be confusing orthogonality with polar alignment

 During calibration, all the measurements are strictly in the camera coordinates because PHD doesn't know yet how to map those into the RA and Dec axes.  So when PHD is issuing calibration guide steps on one axis or the other, it has to assume that the guide star movement it sees is a reaction to those commands and the movement is along the axis we’re measuring.  In other words, it assumes the guide star will mostly “stand still” on the other axis.  Obviously, this can’t happen exactly, which is why PHD tries to move the star a long distance in a short time on the axis it's measuring.

In that case, the unwanted movement on the “other” axis should be substantially smaller and will have minimal effect.  For mounts that are working at all, the measurement of the RA axis orientation should be fairly accurate because the Dec motor isn’t running at all.  But if the polar alignment error is huge, there could still be large drift in Dec that will be interpreted as RA movement.  Conversely, if PHD is trying to measure the Dec axis orientation and the mount has a giant periodic error, some part of that error will be interpreted as Dec movement.  In other words, tracking errors on one axis can “bleed” into the measurement results for the other axis.

Common causes of orthagonality errors are
bad polar alignment,
large declination backlash, or
large periodic error in RA

In your case, the resulting calibrations are indeed very problematic. Here's an example of the steps showing no clear spacing in each direction, and RA and Dec appear opposites of each other. Your guiding will be severely compromised, and any subs you can save really have nothing to do with the quality of guiding.

If you want to explore this, you should probably start with PHD's star cross test to see how your mount performs in each of the four directions. My guess is it probably won't look good, but it's a place to start. Make sure you bump the mount north to clear any dec backlash prior to calibrating, that may help. 

I also noticed your mount type is "unrecognized" Skywatcher? Is that correct?

Mount = SkyWatcher driver,unrecognised model #50

 

Brian

On Wed, Jun 7, 2023 at 8:49 PM Tom Johnson <runth...@gmail.com> wrote:

So I have a Celestron Nexstar 8se on a Skywatcher EQM-35 Pro. Been using for a couple of years with an external guide scope and guiding was ok with the .63 reducer but not so great without reducer due longer focal length. Thought I would get the ZWO OAG and see if I could improve my guiding a bit, but so far not the case. No matter what I do when I calibrate I get a message about RA and Dec angle being questionable, and when I look they are either both in the same direction or close to 180 degrees apart in exact opposite directions rather than perpendicular. Not even sure how that is possible. I use polemaster to polar align, and even with the questionable guiding or no guiding I'm still able to keep about half my subs so don't think it is a polar alignment issue. My guide camera is ZWO asi290mm mini with pixel size of 2.9 and my focal length with .63 reducer is 1298, but per astometry.net it is actually closer to 1198 so have those values entered. Have tried running Guiding assistant, but that hasn't changed anything either. Any advice is appreciated.

 Here's a link to my latest PHD2 log file, https://openphdguiding.org/logs/dl/PHD2_logs_GPNR.zip

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Brian Valente

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[mj.w...@gmail.com]

Hi Tom

1)  "Mount = SkyWatcher driver, unrecognised model #50"

From what I've read this is a problem with Skywatcher's mount driver.

Try switching to an EQMOD setup.

  

2)  You should try Binning the guidecam.

This will double the pixel scale   Pixel scale = 0.50 arc-sec/px,     which is a result of the guidecam having unusually small pixels  pixel size = 2.9 um

And will increase sensitivity, always a bonus with an OAG.

(Make a new Equipment Profile with a unique name)

3) Dec Calibration was dominated by Dec Backlash,  11 steps in one of the Calibrations.

Clear the Dec backlash by stepping north until you see the guidestar moving, then start the Calibration.

Here's some advice from the Experts:

https://openphdguiding.org/phd2-best-practices/

https://github.com/OpenPHDGuiding/phd2/wiki/EQASCOM-Settings

Michael

Wiltshire UK

[Tom Johnson]

Thanks for the reply Brian.

I apologize in advance if I am misunderstanding anything in your reply, just trying to reply to see if I do understand or am misunderstanding any parts.

As to the orthogonality vs polar alignment, not sure I follow. The first thing I do once all connected is polar align using PoleMaster with QHY Polemaster cam/scope, well before anything in PHD2. Not saying the polar alignment is perfect, but should be pretty close.

Then I align my Skywatcher EQM-35 pro making sure my last movements are Up and Right, believe I read that somewhere a long time ago, but don't remember where.

Then fire up PHD2 to calibrate. I know until it completes a calibration it has no idea which direction is RA or Dec which would depend on guide camera rotation as well is probably several other factors.

It has complained about Dec backlash at times from the beginning. I did notice it seemed a bit loose yesterday so thought maybe that was causing the issue so snugged it up as much as I could without causing any binding and there is little to no visual or audible backlash now.

Again, been using this same mount and PHD2 for about 2 years, the only change was the OAG and new asi290mm mini, was using the asi120mm mini with the external 50 mm guide scope.

I'll give the star cross test a try and see what it looks like.

[Tom Johnson]

Thanks for the reply Michael.

1. I tried figuring out the EQMOD setup once before, but couldn't figure it out. Seemed like there was something different about the 35 vs the 5 and 6R that couldn't seem to get it working, but maybe I'll look into it further. I was using it as setup now for almost 2 years so at the time decided don't try to fix what wasn't broken, but may be more worth it to me now.

2. I'll try binning and see if it helps.

3. I always finish my mount alignment with up and right movements which I believe should be north, but I'll try bumping it north with the ASCOM applet to be sure next time.

[bw_m...@earthlink.net]

You should upgrade to the latest 2.6.11dev6 release which contains the new Calibration Assistant.  Then follow the other recommendations for creating a new configuration profile with 2x2 binning.  Be sure you know what the mount’s guide speed setting is, don’t just guess or blindly accept the default value. When everything is connected and you are reasonably well polar-aligned, run the Calibration Assistant (under the ‘Tools’ menu) and follow all of its recommendations.  This will eliminate a variety of operational problems that may be complicating the picture.  That said, I doubt it will fix the problem in which case you should run the Star-Cross test to see if the mount can be guided successfully in all 4 directions.

 

https://openphdguiding.org/development-snapshots/

 

https://openphdguiding.org/man-dev/Tools.htm#Calibration_Assistant

 

Good luck.

 

Bruce

 

If you want to explore this, you should probably start with PHD's star cross test to see how your mount performs in each of the four directions. My guess is it probably won't look good, but it's a place to start. Make sure you bump the mount north to clear any dec backlash prior to calibrating, that may help. 

 

I also noticed your mount type is "unrecognized" Skywatcher? Is that correct?

Mount = SkyWatcher driver,unrecognised model #50

 

Brian

 

On Wed, Jun 7, 2023 at 8:49 PM Tom Johnson <runth...@gmail.com> wrote:

So I have a Celestron Nexstar 8se on a Skywatcher EQM-35 Pro. Been using for a couple of years with an external guide scope and guiding was ok with the .63 reducer but not so great without reducer due longer focal length. Thought I would get the ZWO OAG and see if I could improve my guiding a bit, but so far not the case. No matter what I do when I calibrate I get a message about RA and Dec angle being questionable, and when I look they are either both in the same direction or close to 180 degrees apart in exact opposite directions rather than perpendicular. Not even sure how that is possible. I use polemaster to polar align, and even with the questionable guiding or no guiding I'm still able to keep about half my subs so don't think it is a polar alignment issue. My guide camera is ZWO asi290mm mini with pixel size of 2.9 and my focal length with .63 reducer is 1298, but per astometry.net it is actually closer to 1198 so have those values entered. Have tried running Guiding assistant, but that hasn't changed anything either. Any advice is appreciated.

 Here's a link to my latest PHD2 log file, https://openphdguiding.org/logs/dl/PHD2_logs_GPNR.zip

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Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

nature portfolio brianvalentephotography.com 

other astronomy https://www.brianvalentephotography.com/astrophotography/ 

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[Brian Valente]

Hi Tom

>>>As to the orthogonality vs polar alignment, not sure I follow.

What i was trying to convey regarding your ortho error is that based on your comments regarding your "good" polar alignment, it is probably not an issue, so it's better to look at the other contributors. An ortho error of 180 degrees is about the most extreme you can get, so something is not correct in the mount or elsewhere

the star cross test should help point you in the right direction on this

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/615f6d8e-c8ab-49c1-8ce1-8c9e3a73ab93n%40googlegroups.com.

[Tom Johnson]

Ok, got it. Thanks Brian.

[Tom Johnson]

Appreciate it Bruce. I downloaded and installed 2.6.11dev6 and will run through all those tonight skies permitting.