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Equipment Discussions >> Mounts

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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
CG5 Polar Alignment
      #3864563 - 06/14/10 03:47 PM

What would be considered a good polar alignment (point of diminishing returns) for a CG-5? I've gotten AZ -00:43:55, AL -00:13:35 and I think i'm pretty happy.

By the way I'm new to CN so hello to everyone and I'm sorry if I've posted this wrong.


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Fred1
Carpal Tunnel
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Reged: 09/19/07

Loc: Somewhere in the Orion Spur
Re: CG5 Polar Alignment new [Re: tomo]
      #3864596 - 06/14/10 03:58 PM

Welcome to Cloudy Nights.
Ya know? I rarely check the offset in my CG5's. But I consider that I have a good Polar Alignment when my tracking keeps my objects centered for 10-15 minutes before I notice drift. I'm visual only, so the APer's will likely chime in with a more technical reply.


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tomo
professor emeritus
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: Fred1]
      #3864614 - 06/14/10 04:07 PM

Cheers Fred. Perhaps you wouldn't mind taking a second during your next session, looking them up and posting back. My sense if these are good and I don't want to redo and make it worse (if that is possible).

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Fred1
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Reged: 09/19/07

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Re: CG5 Polar Alignment new [Re: tomo]
      #3864805 - 06/14/10 05:33 PM

I'll try to remember to do that, tomo, but please don't scold me if I forgot to post back. You can always PM me if you like.

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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: Fred1]
      #3879829 - 06/22/10 02:18 PM

After having to redo my alignment after a "wild slews" issue, I now have PA accuracy of just less than 15 arc-min on both AZ & AL. Don't know if I should try and do better next time or I run the risk of making it worse. Can anybody help?

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Chris Rowland
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Reged: 02/28/05

Re: CG5 Polar Alignment new [Re: tomo]
      #3880178 - 06/22/10 05:08 PM

I think that's pretty good but if you have a permanent setup I'd try to improve it.

First, do a really good 2+3 or 4 * alignment using a reticle EP. If you haven't got a reticle EP forget it.

Then do a polar alignment but pay attention to the amount of change the scope expects, if it's more than 20 to 25 arc minutes don't fix it.

Hope that helps,

Chris


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vlad10
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Reged: 04/20/06

Loc: Alicante (Spain)
Re: CG5 Polar Alignment new [Re: Chris Rowland]
      #3881377 - 06/23/10 10:20 AM

Use a polar alignment program and a ccd. I use WCS to measure drift with a camera, in less than an hour I get within 3-4 arc minutes in either axis. The HC values are not always correct, you have to actually measure it yourself to realize how close/far you are

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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: vlad10]
      #3881827 - 06/23/10 02:03 PM

thanks vlad10, that sounds like a plan.

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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: Chris Rowland]
      #3881828 - 06/23/10 02:05 PM

Thanks Chris. What is the ploar alignment accuracy you have achieved?

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Chris Rowland
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Reged: 02/28/05

Re: CG5 Polar Alignment new [Re: tomo]
      #3882381 - 06/23/10 07:03 PM

5 to 10 arc minutes

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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: Chris Rowland]
      #3918717 - 07/13/10 10:31 AM Attachment (48 downloads)

So last light my perseverance paid off. Now I have a PA of 2 arc mins in both axes. I simply did 2+4 align then ASPA and repeated. The only difference was that I made the mount level according to the bubble level (which I previously ignored because I can eyeball that it isn't level and an electronic level confirms). To confirm I did a quick DSLR drift 2m exposure at +1 movement and only a few pixels out. I'm sure be tempted to tweek but I'll try not to. Now what PEC or Backlash?

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dwitek
sage
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Reged: 07/03/08

Loc: White Lake, Michigan
Re: CG5 Polar Alignment new [Re: tomo]
      #3918890 - 07/13/10 11:57 AM

The CG5 doesn't have PEC and backlash is a matter of your individual mount. A lot has to do with the adjustment of the mesh of the worm gear. I recently went through a supercharging exercize with mine and now have the backlash settings around 5, others may need upwards of 50. Depends on how much play there is.

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rmollise
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Reged: 07/06/07

Re: CG5 Polar Alignment new [Re: tomo]
      #3919060 - 07/13/10 01:31 PM

Quote:

So last light my perseverance paid off. Now I have a PA of 2 arc mins in both axes. I simply did 2+4 align then ASPA and repeated. The only difference was that I made the mount level according to the bubble level (which I previously ignored because I can eyeball that it isn't level and an electronic level confirms). To confirm I did a quick DSLR drift 2m exposure at +1 movement and only a few pixels out. I'm sure be tempted to tweek but I'll try not to. Now what PEC or Backlash?




Levelling has no effect on polar alignment, though it may make it easier for some folks to do a drift alignment.

The CG5 does not have PEC.


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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: rmollise]
      #3919296 - 07/13/10 03:29 PM

Thanks Rod. I knew leveling has no effect but it just "seemed" to work for me. Know I'm on the button I'll try not to mess it up again. I'm thinking that PA alignment, with all the factors taken in, has variability that means you will never know how right it is. (I'd love to know what this +/- margin of error is). So I chose to do the DSLR method to confirm in a non-computational way.

Is their any software out there that does PEC correction on top of a CG-5 even though there is no internal routine or should I just concentrate on guiding?


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mikewayne3
professor emeritus


Reged: 02/02/09

Loc: San Diego CA
Re: CG5 Polar Alignment new [Re: tomo]
      #3919401 - 07/13/10 04:34 PM

howdy Tomo I set my backlash in the hand control to 01 pos and neg RA as well as Dec other wise it seems to jump when you move it 1 way or the other and I've seen it happen wile I'm guiding so I just make sure of the setting and I'm off and imaging
Mike


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rmollise
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Reged: 07/06/07

Re: CG5 Polar Alignment new [Re: tomo]
      #3919588 - 07/13/10 06:22 PM

Quote:

Thanks Rod. I knew leveling has no effect but it just "seemed" to work for me. Know I'm on the button I'll try not to mess it up again. I'm thinking that PA alignment, with all the factors taken in, has variability that means you will never know how right it is. (I'd love to know what this +/- margin of error is). So I chose to do the DSLR method to confirm in a non-computational way.

Is their any software out there that does PEC correction on top of a CG-5 even though there is no internal routine or should I just concentrate on guiding?




Not that I know of. With a good polar alignment, autoguiding should be enough.


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Foehammer
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Reged: 06/29/06

Loc: Cyprus
Re: CG5 Polar Alignment new [Re: rmollise]
      #3920460 - 07/14/10 03:29 AM

Best numbers I've seen on mine with 2+3 and ASPA (using illuminated reticle ep) were 02" in azm and 01" in alt. this morning...so I guess its good enough?

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rmollise
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Reged: 07/06/07

Re: CG5 Polar Alignment new [Re: Foehammer]
      #3920551 - 07/14/10 07:40 AM

Quote:

Best numbers I've seen on mine with 2+3 and ASPA (using illuminated reticle ep) were 02" in azm and 01" in alt. this morning...so I guess its good enough?




Not sure what you're referring to with 02" and 01"...the polar alignment error the HC reports? It may be good enough...but I wouldn't take what it says too seriously.


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tomo
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Reged: 06/14/10

Loc: Shelby Twp, Mi
Re: CG5 Polar Alignment new [Re: rmollise]
      #3923278 - 07/15/10 01:38 PM

Agapios,
You sure have a fine tuned mount if you have PA correct to 2 arc seconds. Next chance I get I will measure the true error with a WebCam and some software.
Thanks,
Tommy


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Foehammer
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Reged: 06/29/06

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Re: CG5 Polar Alignment new [Re: tomo]
      #3924612 - 07/16/10 03:08 AM Attachment (61 downloads)

Here's what the HC reported that night. Its a cell phone pic hence the bad quality. Too bad I dont keep the mount permanently set up!

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