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Equipment Discussions >> Mounts

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TimP
member


Reged: 02/24/09

Re: Polar Alignment new [Re: jrcrilly]
      #6057784 - 09/01/13 02:34 PM

Quote:

Looks as though (1) lots of dec drift (polar alignment issue) and (2) dec guiding isn't enabled.




Hey John

Before I downloaded the Beta software for my CGEM I was having trouble with PHD calibrating so I believe it automatically shut down DEC guiding. I am still new to PHD and it's settings so if anyone has a good link explaining the settings I would appreciate it.

Tim Patton


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jrcrillyAdministrator
Refractor wienie no more
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Reged: 04/30/03

Loc: NE Ohio
Re: Polar Alignment new [Re: Stargazer78]
      #6057791 - 09/01/13 02:36 PM

Quote:

My display reads
AZM 00 00 00
ALT 00 00 00
That means I am aligned correctly right?




That means only that you have performed the ASPA routine; it says nothing about how well it worked. If the routine didn't work properly you'll have a large polar alignment error but the mount has no way of knowing that. All it can do is to presume that it was done properly and reset the error to zero so it does that. If you want to see how well it worked do another 2 X 4 alignment so those figures can be determined again.

Waiting 15 minutes during ASPA could well make the process invalid. It certainly doesn't intend that anyone stand there and watch for drift.


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Stargazer78
professor emeritus
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: Stargazer78]
      #6057805 - 09/01/13 02:43 PM

What is this up and right you mentioned. I have not been doing this. I have been using all the buttons to center my stars during the alignment and calibration process. The manual doesn't state this!!!!
So when I align and calibrate I should only use the up and right buttons on my hand control? Could you explain this to me please. Just don't understand how nunki can stay centered so long while doing my polar alignment routine. But it makes since that I'm not correctly aligned even though my hand control states I am.


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fetoma
Carpal Tunnel
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Reged: 09/26/06

Loc: Southern New Jersey
Re: Polar Alignment new [Re: Stargazer78]
      #6058016 - 09/01/13 04:53 PM

See this thread:

http://web.archive.org/web/20130727100045/http://www.cloudynights.com/ubbarch...


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Stargazer78
professor emeritus
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: fetoma]
      #6058047 - 09/01/13 05:05 PM

Ok I have not been doing this at all. I have been using all the buttons to center my alignment and calibration stars as well doing this at the beginning of the polar align routine. Now I am wondering if I am the cause of all of my headaches!!!!! so just to be clear on the remote I use the top and right buttons to center my star?

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Stew57
Carpal Tunnel
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Reged: 05/03/09

Loc: Silsbee Texas
Re: Polar Alignment new [Re: Stargazer78]
      #6058057 - 09/01/13 05:20 PM

Yes. Pass the star up with the left and down if you need to use them, then finish with up and right.

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Footbag
Post Laureate
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Reged: 04/13/09

Loc: Scranton, PA
Re: Polar Alignment new [Re: Stew57]
      #6058088 - 09/01/13 05:47 PM

To me, this looks like bad polar alignment. I've had my own troubles with ASPA at times. I found I liked the PHD drift alignment method. The 15m you spent waiting for the star to drift can be cut to seconds using this method. Since you've been aligning with your autoguider, this will be very easy to switch over to. I would probably redo using ASPA and finish easch alignment using up and left. That is, the hand control alignments. You are going to use the altitude and azimuth adjusters for the polar alignment.

Info on the PHD polar alignment method is at the bottom of this link.


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Stargazer78
professor emeritus
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: Footbag]
      #6058115 - 09/01/13 06:04 PM

LOL is it up and right or up and left???

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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Polar Alignment new [Re: Stargazer78]
      #6058120 - 09/01/13 06:10 PM

Quote:

LOL is it up and right or up and left???




My bad. Up and right. Probably why I had troubles with it. Fortunately, a drift alignment doesnt rely on your mounts star alignment to work.


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James74
super member


Reged: 01/29/12

Loc: Sacramento, CA
Re: Polar Alignment new [Re: orlyandico]
      #6058170 - 09/01/13 06:55 PM

Here's an excerpt from a PHD help guide (http://www.rosecityastronomers.org/resources/pdf/GuideToGuiding.pdf):
"12) Max DEC Duration (milliseconds): Same as for Max RA Duration.
Note: It has been suggested that setting max DEC duration to some very high value such as
2000 milliseconds will correct problems with certain mounts, such as the Celestron CGEM.
The problem that is addressed by this setting is that the DEC motor sometimes won't respond
to a small correction due to mechanical issues. It is true that allowing a large DEC correction
will eventually overcome this fault in the mount, but the exposure will already be ruined.
Other than fixing the mount, the only solution to such a defect is to get the polar alignment
good enough that DEC guiding can simply be turned off."

I noticed the same problem on my CG5 and fixed it with this. However, when I increased my Max Dec to 1000ms I started seeing jumps in dec, almost like dec backlash compensation. I'm going to see if using low pass filtering will fix this.


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Peter in Reno
Postmaster
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Reged: 07/15/08

Loc: Reno, NV
Re: Polar Alignment new [Re: James74]
      #6058181 - 09/01/13 07:11 PM

+1 what James said.

Celestron mounts are notorious for excessive Dec backlash. I had the same issue with CPC0800 but CGEM as well as other Celestron mounts also have same issue. The best way to minimize Dec backlash issue is to increase PHD Max Dec duration to about 1500-2000msec. This helped me quite a bit but it's not 100% perfect. It's a mechanical issue found in all Celestron mounts. You get what you paid for. I upgraded to Astro-Physics Mach1GTO and Dec backlash was practically eliminated but costs about 4 times more than CGEM.

So, start with PHD Max Dec Duration of about 1500msec. This usually solves Dec backlash issues. Do not set any Dec backlash compensation in CGEM hand controller, leave it at 0.

Peter


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Stargazer78
professor emeritus
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: Peter in Reno]
      #6058227 - 09/01/13 07:56 PM

Just got off the phone with James. I am about 95 percent sure I am the error and not the mount! Gonna try again tonight if the clouds break.

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Raginar
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Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Polar Alignment new [Re: orlyandico]
      #6058263 - 09/01/13 08:26 PM

Orly, I didn't know that! Thanks

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TimP
member


Reged: 02/24/09

Re: Polar Alignment new [Re: Stargazer78]
      #6058300 - 09/01/13 08:56 PM

Quote:

Just got off the phone with James. I am about 95 percent sure I am the error and not the mount! Gonna try again tonight if the clouds break.




Did you rule out the cogging issue ? I understand about the up and to the right buttons but that still doesn't address the motor getting hung up when it's tracking.

Tim


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Stargazer78
professor emeritus
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: TimP]
      #6058339 - 09/01/13 09:35 PM

I don't think that's my problem. Starting to think it has been poor polar alignment all this time. I just assumed that was the issue because I believed what my display told me

Edited by Stargazer78 (09/01/13 09:36 PM)


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TimP
member


Reged: 02/24/09

Re: Polar Alignment new [Re: Stargazer78]
      #6058389 - 09/01/13 10:15 PM

Quote:

I don't think that's my problem. Starting to think it has been poor polar alignment all this time. I just assumed that was the issue because I believed what my display told me




It wouldn't hurt to join Team Celestron. It's free and you can get some good information.

Tim


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Bill W.
Carpal Tunnel
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Reged: 10/09/05

Loc: Western PA, USA
Re: Polar Alignment new [Re: TimP]
      #6058764 - 09/02/13 07:25 AM

You definitely have the Dec cogging issue. Go to teamcelestron.com and apply to be a beta tester. You can download the beta firmware and try it. if it doesn't work you can always go back to the original firmware. I have a CGE Pro and had the same issue but it wasn't as severe as you're dealing with.


-Bill


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Stargazer78
professor emeritus
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: Bill W.]
      #6059441 - 09/02/13 02:47 PM

Well guys I am a little embarrassed here. I do not have the dec cogging issue. I watched a you tube video of that problem and I don't have it. What I do have is operator error! I assumed that my polar alignment was right and in doing so mistook being way off the pole for this dec cogging issue. I want to thank everyone for all your responses. It helped me narrow down my issues..... myself and poor polar alignment!

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fetoma
Carpal Tunnel
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Reged: 09/26/06

Loc: Southern New Jersey
Re: Polar Alignment new [Re: Stargazer78]
      #6059553 - 09/02/13 03:49 PM

That's cool. This is what we do here to help each other out. Troubleshooting your issues will help someone else's issue down the line. It's what makes these forums an this community so valuable!

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