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HELP ! I have a guiding problem.


Graham
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I need to put this out to you good people to get some input on my problem. :blink:

I have in the past done many subs of 1200 seconds with no problems.

I stripped and rebuilt my much modified EQ5 mount and put it back on the pier.
After setting up all my Astro programs on a single computer ( I used to run 2 one for the imaging and one for the mount)
I now have a peculiar problem. :screwloose:

When guiding with PHD the lines on the graph are pretty much flat as normal however the mount is drifting in DEC quite alarmingly. :o
I can sit and watch the DEC coordinates climb on the EQMOD panel.

This makes even 300 second subs impossible as the stars are oval.

How can this be. :wallbash:
The graph is telling me it is guiding spot on, the pictures tell a far different story.

I am confused to say the least. :chin_scratch2:

Any ideas.

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Have you calibrated the guiding? I had to force a calibration when I inadvertently altered the guide scope orientation.


 


Make sure you have not turned off the dec guiding or reversed it. Those would be my forst checks after of course making sure that balance is as it should be and that both motors are actually working.


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Have you calibrated the guiding? I had to force a calibration when I inadvertently altered the guide scope orientation.

 

Make sure you have not turned off the dec guiding or reversed it. Those would be my forst checks after of course making sure that balance is as it should be and that both motors are actually working.

 

Hi Mike.

Yup all calibrated

Set up is exactly as before with the 1200 second subs.

Both motors are fine.

 

To give you some idea of the drift I was trying to get the horse head tonight.

starting DEC coordinates were  - 02 . 27 . 14 after 5 mins the DEC coordinates were - 02 . 30 . 28

 

But the lines on the PHD graph were constant and pretty much flat on the center line.

 

Just doesn't make sense to me.

If the graph line was consistently below the center line I could understand it.

Weird to say the least.

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double check PA to within an inch of it's life and or drift align, it sounds like it may be field rotation caused by bad PA. This should cause some parts of the image to be a lot worse than others if that is the case.


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Got to be worth a look agreed but I would expect a field rotation to be an RA problem not DEC.


Mind thinking about it I did try turning the DEC guiding off to see what happened in just RA and it went bloody mental.


 


I do have another issue in that when I do the calibration the yellow dotted lines do not show up on the screen for a good 20 - 30 steps which is way past the needed amount.


That never happened when I was running 2 computers.

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Is the guide star in the middle of the PHD image? If it is then the star could appear stationary in x-y (hence flat PHD graphs) but the image is actually rotating around it. This rotation is magnified the further the guiding star is from the centre of the DSO you are imaging.


 


In my case my imaging scope points quiet a long way off axis compared to my guide scope.


 


"I do have another issue in that when I do the calibration the yellow dotted lines do not show up on the screen for a good 20 - 30 steps which is way past the needed amount. That never happened when I was running 2 computers." What training step do you have set?. When guiding what max movement do you have set?


 


And I hate to say it but, did you put the mount back together right?

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Is the guide star in the middle of the PHD image? If it is then the star could appear stationary in x-y (hence flat PHD graphs) but the image is actually rotating around it. This rotation is magnified the further the guiding star is from the centre of the DSO you are imaging.

 

In my case my imaging scope points quiet a long way off axis compared to my guide scope.

 

"I do have another issue in that when I do the calibration the yellow dotted lines do not show up on the screen for a good 20 - 30 steps which is way past the needed amount. That never happened when I was running 2 computers." What training step do you have set?. When guiding what max movement do you have set?

 

And I hate to say it but, did you put the mount back together right?

 

Yes the mount is correctly assembled.

I set the training steps at 2000 which is where I had it before on the other computer..

Max movement is set at 0.1, but I tried 0.05 and 1 as well.

I used several guide stars as well as changing the pier side of the scope but all to no avail.

I will point out that on the other computer the programs were all at least 2 years old. I am now using the latest versions of all software.

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Oh, so everything changed at once!


 


I would go back to old software on one computer and prove the mount is OK.


 


Then old software versions but on split between 2 computers and prove the 2 computer idea is OK.


 


Then upgrade software on each computer in turn.


 


The concept of 2 computers is sound, me and Red Dwalf do this at every star party.

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Glider.


The reason for the upgrade was I was having trouble with EQMOD on the old set up.


EQMOD started to keep crashing if I had CDC and PHD running at the same time.


In fact it would crash for no reason even if I just had only one of the above running.


 


Ron


Thats interesting I might just try that.


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Just to play devils advocate so to speak.

If the PA is that far out surely it would show up on the guiding graph as PHD would have to keep adjusting the mount to compensate.

Not really Graham, All the guiding graph is telling you is that phd is keeping the telescope is pointing consistently at the guide star, if PA is out then stars are free to rotate around the guide star.

Check your images are the trails better in one area than another? If your using a separate guide scope with a shorter fl then the stars will be good in the guide scope but alignment issues will be magnified in the imaging rig.

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I have always set the guide camera 90 degrees to the imaging camera.


The imaging camera is set with the chip horizontal and the guide camera with the chip vertical.


Some thing I read about a long time ago but it does make a lot of difference to the guiding.


Do not ask me why but it does make a difference. :2thumbsup:


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Quoting Craig Stark himself and lifted from a thread by Dion on Astronomy Shed.........................

 

Craig Stark's official word on the subject, the first sentence is his reference to the synguider i mentioned to him :-

--------------------------------------

I've never seen in person, much less used one and so I don't know what it needs. But, I can say that PHD doesn't give a hoot about the orientation. Setting it up "square" can help you read the log file a bit (in particular the calibration section) but PHD's guiding accuracy isn't affected.


During calibration, PHD determines two vectors - one for RA and one for Dec. For any error (displacement from the lock position) we have another vector. You can ask how much of that vector lies along the RA and how much along the Dec (you just calculate the dot product of the vectors). So, RA/Dec becomes a pair of axes just like X and Y. The fact that they're rotated relative to X and Y doesn't matter as, by doing this dot product (or "projection") you get into RA/Dec "space".


Craig
-------------------------------------------------

 

Having said that, I do align the guide camera!

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