help with Trouble-shooting phd2 guiding after useing QHY polemaster

[sami aldoseri]

Hi

After receiving the QHY polemaster  this week, I start  testing  how accurate can i go with it  ,I start noting  very bad guiding ,

 

 

 

from the seeing of the phd2 guiding graph there is bad drift in DEC axes ,i check all procedures with setting up the mount but i an not find anything  missing and i followed up the step  on how to setup  the polar alignment in the  software (V132(beta7),but i do know how accurate is it ???? and where is the error , is there any way to  find how good my polar alignment!!!??? ???

 

I will  attached phd log files ,if  same one would like to helping me  troubleshoot is issue!!!!!, I am using qhy5  2 ,Orion st-80 guide scope on is NEQ6 mount

[peter wolsley]

Sami,

I calculate that your polar alignment error was roughly 5 minutes.  I suspect you can do better with the Polemaster.  What I find troubling is the hugh number of DEC backlash movements.  I estimate that your DEC backlash is roughly 75" which is quite large.  Your focus should be on DEC backlash.  Disable backlash comp in your mount and use the PHD guiding assistant to calculate your DEC backlash. This will give you a more accurate value for DEC backlash. As your polar alignment improves you are going to find that DEC backlash becomes harder to control.  You should try configuring PHD to perform DEC guiding in one direction only.  I find that using the DEC Hysteresis algorithm with 70 to 90% hysteresis works well for me.  I have 50" of backlash in my CGEM.

IMHO your RA guiding is quite good.  There is a dominant 10 second oscillation which has an amplitude of 0.5" Peak to Peak.  You may want to search the web forums to learn more about this 10 second oscillation.  Your mount's residual PEC is small so I suspect you have already trained your mount's PEC.

Certainly learn how to use your Polemaster but your focus needs to be on reducing DEC backlash and avoiding triggering DEC backlash events.

Peter. 

[bw_msgboard]

HI Sami.  The answers to your questions should come from running the Guiding Assistant for an extended period of time.  It seems pretty clear there’s a large amount of Dec backlash in your mount and that’s probably most of your problem.  Try running the GA for 10 minutes or so, then let it measure the Dec backlash.  To measure the Dec backlash, choose a guide star near the south side of the frame so the GA has plenty of room to push the star north during the backlash test.  The GA will also give you a direct measure of your polar alignment error which is probably already pretty good.  When you get all that done, post both the guide log *and the debug log* files so we can help you understand the results.

 

Good luck,

Bruce

 

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[sami aldoseri]

Hi Peter

Thank you for your assistance on troubleshooting

I find is issue before with eq6 dovetail and I think I fix it, you see this video for more info https://youtu.be/_fi9mOErYfo

Do you think that this issue is main problem in my mount ???,i try to solving the is problem always seem to cam back

I will update the post with the result

Regards
Sam

[sami aldoseri]

Hi Bruce

Thank you for your assistance

tomorrow I would do the test and I will update you with the results with log & dubg files

Best regards
Sam

[sami aldoseri]

hi

 i would like to update you about the issue that i have with the bad guiding  , in the attach you will  find the  PHD Log file& dubg files as  MR. Bruce recommended  after some tune up on  the NEQ6 mount , i run the GA for 10 minutes and i used  Hysteresis algorithm for DEC  as MR. peter suggested to me, i used qhy polemaster for polar alignment , still i see  same small drift in DEC as below

https://drive.google.com/file/d/0B9_ar89-fsR6QWR6NERwWS1SaVk/view?usp=sharing

i don't know what is wrong !!!!!!??????? , why i can not get reasonable guiding ????

if some one can  list me the guiding procedure & steps with phd2 probably i can find what is missed and  where is the problem,  like  ( making  sure about leveling the mount & balance the mount & polar alignment )
 
so i hope that we can solve the problem

best regards
sam

[Andy Galasso]

On Mon, Oct 24, 2016 at 3:24 PM, sami aldoseri <ssdo...@gmail.com> wrote:

i don't know what is wrong !!!!!!??????? , why i can not get reasonable guiding ????

Sam,

It looks to me like you are getting reasonable guiding.  In most sections of the log your combined RMS error is less than 0.5 arc-seconds which should give you nice round stars in your imaging camera.

Are you concerned about this section of your guide log?

If so, that was a one-time incident, probably caused by a gust of wind, a cable snag, or something bumping into the gear. Definitely nothing to do with your guiding procedure or PHD2 settings.  Other than that incident, the guiding looks pretty good to me.  Was that the part you were concerned about, or is it something else?

Andy

[sami aldoseri]

hi Andy

thanks for you participation

i am head to Narrow Band Imaging, so  i need to get sub frames from  900 to 1200 like you know, with this this long subs i always have Egg-Shaped Stars in same of side  my frames ??? i try to  solve lot of  issues and i and solve most , I know that, the  problem not direct with PHD2,  bout how can i know that phd 2  setting  not part from problem  ????,   i need  help here !!!!??

i did measure DEC backlash  WITH phd2 GA and it  shows it normal ?,???? and  to make my NEQ6 mount high in performances, i  hyper-tune the NEQ6 and  upgrade it with belt-mode and  add QHY polermaster to  reach me goal with Astro Imaging .

so  my conclusion is  (polar alignment drift or not perfect guiding or  the mount not level well or all the reasons before )

if can you give you opinion i will be thankful

best regards

sam


On Monday, 24 October 2016 23:27:54 UTC+3, Andy Galasso wrote:r

[sami aldoseri]

Dear Pater

i upload new log file probably you can have look on it

thanks

[Andy Galasso]

Sam,

Are you using an OAG or a separate guide scope? And what is your imaging scope?

Your guiding performance of less than 0.5" combined RMS error would not produce egg-shaped stars.  More likely causes could be optics (e.g. collimation) or differential flexure.  Elongation on one side of the frame would indicate an optics problem; if it the elongation is uniform across the frame, it's likely a differential flexure problem. There's a good section on differential flexure in Bruce's troubleshooting tutorial.   You could post a link to a raw FITS image from your imaging camera and we could give our opinion of whether or not it is a guiding-related problem.  If you do post an image, please also post the PHD2 Guide log that covers the time of the image, and let us know the time of the image exposure (start time and duration) so we can correlate with the log.

Andy

[sami aldoseri]

hi Andy

i am using orion st-80 with qhy5l ii for guiding Pixel scale  1.93 arc-sec/px , and lunt 80mm ED with QHY9S FOR imaging Pixel scale  2.49 arc-sec/px ,will try to get fresh date to night,and upload it

regards

[peter wolsley]

Sami,

Your latest log file indicates a polar alignment error of 4 to 5 arc minutes (3 hr guiding session).  It also shows that your DEC guiding is quite active with several backlash movements.  You did try hysteresis guiding for DEC but you should try a hysteresis setting of between 80 and 95%. I like high hysteresis guiding because the initial guide movements are always small and build up if needed.  My opinion is that it's always better to start with a nudge because it seems too easy to bump the DEC axis too far which then initiates a backlash movement.  The other guiding method for DEC that you should look into is to use one-direction guiding (i.e. North or South). 
  My opinion is that if you had better polar alignment that your backlash movements would have been larger and longer.  The Polemaster claims to be capable of better polar alignment but you need to get control of your DEC movements first.  

If you are using a separate guide scope, you should look into securing it more if differential flexure is suspected.  I use a separate guide scope with a QHY5II camera and I tend to put a little tension on the USB cable so that it tries to pull the camera towards the main scope. I may look into using foam blocks to push against the front and rear of the guidescope.  The issue being to apply some preload to the guide scope but still be able to collimate it with the main scope.

Peter

[John Stiner]

Sami, just to make sure it's not an easy fix, when you install the Pole Master, is the USB cable exiting from the left (east) side of the mount when you are facing it?

[Ray Gralak]

Hi Peter,

>Your latest log file indicates a polar alignment error of 4 to 5 arc minutes (3 hr guiding session).

>  My opinion is that if you had better polar alignment that your backlash movements would have been larger and longer.

> The Polemaster claims to be capable of better polar alignment but you need to get control of your DEC movements first.  

I haven't looked at the logs and you may be correct that polar alignment error is 4-5 arc-minutes, but 3 hours of guided operation will almost certainly bring into play flexure and other effects. These effects can change the cumulative RA/Dec drift rates, thus reducing the accuracy of a polar alignment error calculation. This is why polar alignment methods that involve slewing to different parts of the sky are often less accurate than other methods. 

-Ray Gralak

[sami aldoseri]

Hi john

 yes the USB cable exiting from the left (east) side of the mount with power cable hand control cable, i am using atmospheric refraction opinion to!!, there is new software for 2 days ago i will try to see if i can get accurate polar alignment

[sami aldoseri]

Hi Pater

i  try a hysteresis setting  between 60% to 70%, i will increase it next session and i will search for any flexure between the Orion ST-80 & QHY5L II .

regards
sam

[peter wolsley]

Ray,

I agree with your comments.  With my Celestron CGEM, polar alignment figures change over time and with where the OTA is pointed because of the effects you mention.  My worry for Sami is that at his current DEC drift rate he is seeing a lot of DEC backlash movements.  My experience has shown me that as you reduce your DEC drift rate (i.e. better PA) that it becomes easier to trigger DEC backlash.

Peter