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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
CGEM-DX will not guide in dec
      #6053815 - 08/30/13 04:51 AM

Tonight was my first actual test of my new DX. I was having issues with my polar alignment routine though. I did the normal 2 star alignment plus 4 calibration stars. I then did the ASPA routine. Instead of an eye piece I used my orion auto guider and PHD. Adjusted both azimuth and elevation until my star was centered in the bullseye. turned off the mount and started up again with the same setup. Found my target and fired up PHD. Once it was guiding I checked the graph and my RA was perfect. My DEC climbed off the chart. What did I do wrong?

Edited by Stargazer78 (09/01/13 12:40 AM)


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T1R2
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Reged: 06/11/13

Loc: NeverWhere, 35*N
Re: Polar Alignment new [Re: Stargazer78]
      #6053832 - 08/30/13 05:05 AM

I think because you turned off the mount, once your aligned go ahead and take a *tour*, I would think if you turn it off you will have to start all over again, I don't have the same mount as you but its similar(CGE) you might have to re-enter your location if it is turned off, unless it remembers it. It was odd that you would have to turn off your mount to start to use it, or use the hibernate function. Make sure your real time clock is on.

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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Polar Alignment new [Re: T1R2]
      #6053900 - 08/30/13 07:22 AM

You need to redo the 2+n alignment after turning the power off.

But if you do ASPA you do NOT need to realign!

At most undo sync.

The ASPA alignment rotates the align model by the amount of the polar align error so as long as you do a good job of centring the PA star in both the Sync and polar align phases gotos should still be OK.

At least try it.

Chris


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ohata0
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Reged: 03/10/09

Loc: Hawaii, USA
Re: Polar Alignment new [Re: cn register 5]
      #6054050 - 08/30/13 09:32 AM

ah, i keep forgetting that aspa syncs the star. i should try undoing the sync.

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rmollise
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Re: Polar Alignment new [Re: ohata0]
      #6054081 - 08/30/13 09:55 AM

No turning on or off or redoing the go-to alignment will help his problem. If I read his post correctly, he was showing lots of declination drift while PHD was guiding. That means a problem with polar alignment. Be sure to use a star to the south, one not too high. 30-degrees or so, for ASPA.

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David PavlichAdministrator
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Re: Polar Alignment new [Re: rmollise]
      #6054213 - 08/30/13 11:20 AM

And if you have the time, do two iterations of the PA routine. It will refine your PA and you'll be happy!

David


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dragonslayer1
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Reged: 02/25/12

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Re: Polar Alignment new [Re: David Pavlich]
      #6055233 - 08/30/13 10:29 PM

Please keep us posted how it works out
Kasey


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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: dragonslayer1]
      #6055241 - 08/30/13 10:34 PM

Gonna try again tonight. Fingers crossed lol

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Peter in Reno
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Re: Polar Alignment new [Re: Stargazer78]
      #6055268 - 08/30/13 10:53 PM

I never understand the need to power down the mount after any kind of calibration or polar alignment. If you need to redo the alignment, simply slew to a star, press "ALIGN" button and follow the on screen instructions. It's a lot faster and just as accurate than to power down the mount. It's absolutely unnecessary to power down the mount to redo or check the alignment.

Peter


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A. Viegas
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Re: Polar Alignment new [Re: Stargazer78]
      #6055276 - 08/30/13 11:01 PM

Pick a star close to the Meridian and near the celestial equator... Try Some of the stars in Ophiucus... Like Cebalrai, Altair or Rasalhague as your polar alignment stars in the early evening

Al


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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: A. Viegas]
      #6055393 - 08/31/13 12:52 AM

I used Nunki. Still having the same issue. Guiding great in RA DEC is off the chart. Using default brain settings and my mount says im perfectly aligned??,

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Alph
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Re: Polar Alignment new [Re: cn register 5]
      #6055471 - 08/31/13 03:05 AM

Quote:

At most undo sync.



No need for it and it is easy to verify it.


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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: Alph]
      #6055496 - 08/31/13 03:49 AM

Ok I think I have found a solution. My goggle fu was great tonight! Sine of these mounts were having issues guiding in dec. Example would be my phd guide graph. After searching several old threads frim different sources I stumbled in a topic that celestron was making a firmware solution for this exact problem. Then I thought, hey its after midnight might as well try and see if there was a update and..... yep. I updated my firmware and re did a rough polar alignment through my polar scope. Re dud the alignment and fired up phd. At this point I just wanted to see how the graph was doing. Even though my alignment was off they both tracked decent. They were not running on the center line but I could tell just from the graph that it was improving. If I would of done a proper polar align I'm sure this solved my issue. If someone else has had this issue please chime in and tell me what you did to fix this. Im about 95 percent sure tomorrow night will be good.

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mskillen
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Re: Polar Alignment new [Re: rmollise]
      #6055538 - 08/31/13 05:14 AM

Quote:

No turning on or off or redoing the go-to alignment will help his problem. If I read his post correctly, he was showing lots of declination drift while PHD was guiding. That means a problem with polar alignment. Be sure to use a star to the south, one not too high. 30-degrees or so, for ASPA.




This I didn't know thanks for this info, I guess the reason for this is these stars are further from the celestial pole?
I was just picking a star and going for it before I will try this out and see if it helps me.

Mark


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rmollise
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Re: Polar Alignment new [Re: Peter in Reno]
      #6055669 - 08/31/13 08:58 AM

Quote:

I never understand the need to power down the mount after any kind of calibration or polar alignment. If you need to redo the alignment, simply slew to a star, press "ALIGN" button and follow the on screen instructions. It's a lot faster and just as accurate than to power down the mount. It's absolutely unnecessary to power down the mount to redo or check the alignment.

Peter




The reason for this is that early on, in the days when the polar alignment routine used a single star, Polaris, Celestron did advise you to turn the mount off after the alignment and do a new go-to alignment. That's no longer the case, but it's what people remember. Also, it's not really much harder than hitting the Align button.


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dragonslayer1
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Re: Polar Alignment new [Re: rmollise]
      #6055727 - 08/31/13 09:44 AM

Am glad for you Stargazer, I hope the upgrade fixed everything and all is well; again, keep us posted,
Kasey


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orion69
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Reged: 05/09/10

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Re: Polar Alignment new [Re: Stargazer78]
      #6055739 - 08/31/13 09:58 AM

Quote:

Ok I think I have found a solution. My goggle fu was great tonight! Sine of these mounts were having issues guiding in dec. Example would be my phd guide graph. After searching several old threads frim different sources I stumbled in a topic that celestron was making a firmware solution for this exact problem. Then I thought, hey its after midnight might as well try and see if there was a update and..... yep. I updated my firmware and re did a rough polar alignment through my polar scope. Re dud the alignment and fired up phd. At this point I just wanted to see how the graph was doing. Even though my alignment was off they both tracked decent. They were not running on the center line but I could tell just from the graph that it was improving. If I would of done a proper polar align I'm sure this solved my issue. If someone else has had this issue please chime in and tell me what you did to fix this. Im about 95 percent sure tomorrow night will be good.




How is your balance, especially in DEC? If you want decent guiding DEC balance must be spot on and RA little (and I mean little) east heavier.

Edited by orion69 (08/31/13 09:59 AM)


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Stargazer78
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Re: Polar Alignment new [Re: orion69]
      #6056916 - 09/01/13 12:18 AM

Scratching my head at this one. No change in behavior. My phd graph is all over the place. I drifted on nunki for 15 minutes and it stayed centered. My polar align display reads...
AZM:-00 00'01
ALT:-00 00'00
It has to be this coging issue I keep reading about. Any one out there who just purchased this mount have this issue? Im using default settings on the hand control and phd.


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Stargazer78
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Loc: Susanville California
Re: Polar Alignment new [Re: Stargazer78]
      #6056956 - 09/01/13 12:51 AM

Cannot get 60s subs even with out guiding!!! This cannot be right????

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orlyandico
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Re: Polar Alignment new [Re: Stargazer78]
      #6057050 - 09/01/13 03:23 AM

You must be using the AT8IN?

If so.. then yes 60 seconds unguided is out of reach.

If you're absolutely sure your polar alignment is dead-on (i.e. no drift in DEC if you turn off DEC guiding in PHD) then you're hitting the large periodic error of the CGEM and CGEM DX.

Try doing a PEC training. This still won't help a lot of your 8/3 error is too large.


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Stargazer78
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Loc: Susanville California
Re: Polar Alignment new [Re: orlyandico]
      #6057083 - 09/01/13 04:15 AM

Quote:

You must be using the AT8IN?

If so.. then yes 60 seconds unguided is out of reach.

If you're absolutely sure your polar alignment is dead-on (i.e. no drift in DEC if you turn off DEC guiding in PHD) then you're hitting the large periodic error of the CGEM and CGEM DX.

Try doing a PEC training. This still won't help a lot of your 8/3 error is too large.




So what am I supposed to do? I bought this mount for astrophotography. The manual doesn't tell me how to do a pec training and honestly I have no idea what that is? I am beyond frustrated at this point!


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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Polar Alignment new [Re: Stargazer78]
      #6057090 - 09/01/13 04:30 AM

Try guiding. This will cope with the uncorrected PEC and the dec drift if you aren't perfectly polar aligned.

How much Astrophotography have you done before? Are you just starting or are you moving to a longer focal length?

Chris


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Stargazer78
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Loc: Susanville California
Re: Polar Alignment new [Re: cn register 5]
      #6057093 - 09/01/13 04:42 AM

Lol. That's my issue I cannot guide at all. That's why I believe I need the beta fix.

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A. Viegas
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Re: Polar Alignment new [Re: Stargazer78]
      #6057273 - 09/01/13 08:58 AM

Ok... Have you used PHD before? Check your settings or post them here. Next verify your polar alignment by re-aligning on two different alignment stars and calibration stars and then check your polar alignment display... Then if necessary redo the ASPA on a star close to the meridian and celestial equator... celebrai or rasalthague should do fine...

Now when you are running PhD are you seeing large spikes in the guiding graph? If so then the guiding problem can be more software than hardware... If your guiding graph does not show big deviations and yet the guiding is still poor with oblong stars as short as 60 seconds then you could have a bad CGeM. If It's still under warranty, send it back, if not then try the beta motor control software...

Oh last comment, what FL are you shooting at? If you are imaging at under 1,000mm then it is a real shame and your CGEM could hve a really bad 8/3 and cogging issue...

Al


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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: A. Viegas]
      #6057285 - 09/01/13 09:14 AM

setup is a AT8IN 800 mm focal length with a orion 80 mm short tube guide scope using an orion auto guider. I start off doing the 2 alignment stars followed by the 4 calibration stars.after that is done I slew the scope south to nunki. I start up the polar alignment routine. Instead of using a reticle eyepiece I use my autoguider with phd guide. I turn on phd with the bullseye. I follow the routine for pa and place nunki right in the center. I will then observe for any drift. I observe for 15 minutes. Once there is no drift. I then confirm the polar alignment routine. I then check my polar alignment display and it will read 00 00 00 for both AZM and ALT. I then go to my target and fire up phd again. Once im guiding I check the phd graph and I get a saw tooth pattern and at times the graph jumps off the chart.i tried unguided and I cant even get 60 second exposures with out trails. I dont understand how I can see no drift when I polar align but my guiding is terrible! Its not making any sense and I am so frustrated!

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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: Stargazer78]
      #6057287 - 09/01/13 09:15 AM

Using all default settings also for phd

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Stew57
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Re: Polar Alignment new [Re: Stargazer78]
      #6057300 - 09/01/13 09:24 AM

You have DEC cogging it sounds like. The beta firmware may fix this but may introduce other problems. You could try swapping the ra and dec motors as only some of the motors have this problem.

One fix you could try is to be off a little in your PA. That way the guiding is always in one direction and greater than the cogging effect. Those that have a problem free CGEM will never understand, as the CGEM is very nice when working correctly, so take it to heart.


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orlyandico
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Re: Polar Alignment new [Re: Stargazer78]
      #6057309 - 09/01/13 09:32 AM

well... if you are sure there is no drift in declination then turn off DEC guiding. see from there.

EDIT. You say all default settings in PHD. These won't work. Go into the brain icon and change the Calibration Step to 2000ms. Normally it's much less than that. I think what is happening is your calibration step was so small so during PHD calibration, PHD had to send a lot of DEC guide commands to overcome the cogging/stiction/whatever so when actually guiding it over-corrects.

But still try to post your PHD guide graph. If you're getting sawtooth in DEC that's either cogging or stiction.

PHD should be able to smooth out even very bad RA periodic error.

Also try using longish guide exposures (say 4 seconds) to smooth out the seeing. Also.... when you calibrated PHD did you do it on a star close to what you want to image?

theoretically you should re-calibrate PHD ("Force Calibration" button in the brain menu) every time you re-point somewhere far from where you did the initial calibration.

Also.. when doing your star alignment when the CGEM DX booted up, did you always end the alignment on each star using only the UP and RIGHT buttons?

oh and Mark, my CGEM is gone. had to eat a huge loss selling it, but can't really say I miss it. I only reply to these threads out of force of habit.


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Cliff Hipsher
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Re: CGEM-DX will not guide in dec new [Re: Stargazer78]
      #6057319 - 09/01/13 09:44 AM

Why not do a drift alignment? As I understand it, if your polar alignment is spot on, you do not to guide in DEC...

One other thing.. Do the stars trail in the same direction in both the guided and unguided images?


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Raginar
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Re: Polar Alignment new [Re: orlyandico]
      #6057333 - 09/01/13 09:56 AM

Orly,

Glad you got rid of your CGEM. Stargazer, let's settle down and make sure we have everything configured before jumping to conclusions. I imaged with an AT8IN on a regular CGEM without much difficulty. The biggest problem I had was differential flexure (the two tubes were flexing as it moved around, causing guiding issues).

So, first off you need to read this:
http://www.cloudynights.com/item.php?item_id=2755

Second, IF you're using ASPA, you'll find that you are Polar Aligned well enough to guide. Your shorttube 80, how is it mounted to the AT8IN? Are you using clam shells? The stock Orion rings? You'll find many people complain about the stock orion rings. I would look for a more secure connection. My personal solution was an ADM MDS system that I bolted to the top of my AT8IN. The ADM rings are much more 'solid' and the MDS gives you a firm connection to the imaging scope. So, there is a possibility that this is the source of your problem. But, lets continue.

Third, you're going to have to change your settings. I usually ended up around 80 on RA aggressiveness. Change your min motion to .2. And, your max movement for RA/Declination to around 1500 for each (probably high but OK for starting). Increase your calibration steps to 2000-4000ms depending on your setup. I use a a mini-guider and I need 4000ms to see adequate movement with my setup. Yours will be somewhere in between. You'll see in the article that you want somewhere between 8 to 20 steps for RA and declination.

One thing on declination calibration. Are you using the relays or ASCOM? I've found on many of the mounts I have owned that declination guiding through ASCOM results in 'backlash'. I don't know why, but I find if I hit the 'up' button a few times when PHD says 'Clearing Backlash...' It will help it figure out a correct calibration. I find if the 'Clearing Backlash..' stays up for more than 2-5 seconds, that's when to do this. This is cited in an article on the Stark Labs Yahoo! Group as well.

Finally, Make sure your guide scope is FIRMLY attached to your AT8IN. Make sure the camera is FIRMLY attached to the extension/focuser/whatever. These are often frustrating sources of guiding problems.

The key to successful imaging is taking a balanced approach. Change one variable at a time and see what it does. Don't make huge changes to your system as you're going to find that introduces more problems that you won't be able to fix once its dark out.

Finally, TRUST ASPA. It works, period dot to an accuracy enough that you will be able to perform guided AP with your AT8IN. Don't mess with your polar alignment past doing one iteration. Just make sure you are doing the 'other gotchas' such as 'up and right' to each star. That you are doing a full 2 + 4 prior to syncing on an appropriate ASPA star. An appropriate ASAP star is one that is near the meridian, but also roughly at your latitude (for me, I look for a star at around 45 degrees off the horizon).

Check your settings in your mount. What is your guide rate at? Make sure it's at around 50%. Turn off Backlash Compensation (aka set to 0). Your mount needs to be balanced 'perfectly'. Great article here:

http://starizona.com/acb/basics/using_balancing_gem.aspx

If you're not balanced in the declination axis (a common problem with newts and SCTs), you'll see some pretty crazy stuff with PHD too.

So, come back with more info and let us know. This will sound harsh, but it's probably not your equipment but user error that is generating your problems. I went through the exact same problems when I started. Now, I have it figured out (some times) .

Good luck,

Edited by Raginar (09/01/13 10:01 AM)


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orlyandico
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Re: Polar Alignment new [Re: Raginar]
      #6057437 - 09/01/13 11:07 AM

I think Min Motion of 0.2 is excessive. We're talking about an 800mm main scope and 400mm guide scope. So a min motion of 0.5 should be good enough.

Didn't know you need 8-20 steps for calibration.. I get by with 3 steps. Maybe that's why my guiding is always jumpy.


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Raginar
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Re: Polar Alignment new [Re: orlyandico]
      #6057490 - 09/01/13 11:32 AM

Orly,

That's from the paper in the Yahoo! Group and personal experience. Anything more than that is... excessive. Anything less, and I get poor guiding performance.

.2 is excessive huh? I never had much success with numbers higher than that. It's based on your image scale correct?


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orlyandico
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Re: Polar Alignment new [Re: Raginar]
      #6057530 - 09/01/13 11:53 AM

The Min Motion is for the subpixel guiding. Most people need 0.1 or 0.2 because they're using very short guide scopes, like 50mm finders or the SBIG eFinder.

But if using a long guide scope, a larger figure is more appropriate. I'm using 0.3, my guide scope is 560mm focal length and my main scope is 600mm. On an OAG I have used Min Motion = 1.


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oo_void
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Re: Polar Alignment new [Re: orlyandico]
      #6057653 - 09/01/13 01:04 PM

IMHO, DEC drift after a good polar alignment is almost always a balance issue (an AT8IN with an ST80 is a lot of gear with weird centers of gravity). Orlyandico's recommendations will help compensate for that in PHD.

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Stargazer78
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Reged: 03/05/13

Loc: Susanville California
Re: Polar Alignment new [Re: oo_void]
      #6057673 - 09/01/13 01:21 PM

Ill give it another go tonight. I have never heard of using the up and right buttons only. Ill change my settings in phd too. My exposures for phd has been 2 seconds. Is it possible I am chasing the seein?

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TimP
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Reged: 02/24/09

Re: Polar Alignment new [Re: Stargazer78]
      #6057701 - 09/01/13 01:39 PM

Quote:

Lol. That's my issue I cannot guide at all. That's why I believe I need the beta fix.




I am still working on my knowledge base at the school of hard knocks on my CGEM DX. I can tell you this though. I had the same problem as you. I hyper tuned the mount which really helped on balancing but I still had problems with not being able to guide. I thought it was my Orion guider so I bought a Starlight Xpress Superstar auto guider. Guiding did not work. Hmmmm !! I downloaded the Beta CGEM software. The slews are now a little jumpy from time to time but I am now guiding. I still had a little problem with making my Orion 80mm guide scope solid so I'm going with an Off Axis Guider. Heck! Celestron even replaced my mount. You live and you learn. If I had the money I would have went with a more high end mount but I don't , So I didn't.


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Stargazer78
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Re: Polar Alignment new [Re: TimP]
      #6057741 - 09/01/13 02:03 PM

PHD GRAPH from last night.



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jrcrillyAdministrator
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Re: Polar Alignment new [Re: Stargazer78]
      #6057746 - 09/01/13 02:09 PM

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

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orlyandico
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Re: Polar Alignment new [Re: jrcrilly]
      #6057754 - 09/01/13 02:14 PM

DEC guiding is enabled "Auto" but Mx Dec is 100.

This is not enough for the DEC guiding to chase the declination drift. Which means your polar alignment is way off. I somehow mysteriously got a fantastic polar alignment, <2 arc-minutes off the pole. I only need a DEC correction perhaps once in 10-15 seconds, and it's only 100-150 ms.

In your case your Mx Dec is 100ms and its drifting away like crazy.

I suspect your ASPA is incorrect because you didn't end all alignment movements with UP and RIGHT.


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Stargazer78
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Re: Polar Alignment new [Re: orlyandico]
      #6057774 - 09/01/13 02:29 PM

Ok so I used nunki to do my aspa. I use my autoguider and phd. I center it using the bullseye. Once its centered I wait for 15 mins before I confirm the polar alignment routine. Could all of my issues be poor polar alignment? My display reads
AZM 00 00 00
ALT 00 00 00
That means I am aligned correctly right?


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TimP
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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
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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
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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
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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
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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
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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
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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
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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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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
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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
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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
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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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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
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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.
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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
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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
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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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