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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
CG5 seems to drift, not steady tracking at all
      #5760971 - 03/27/13 06:13 PM

I have an older CG5 mount head that seems to be having tracking issues. I have noticed that when video streaming, I get some drift in the views, even on a lowly setting of 8 secs with my SCB2k. That should not be my polar alignment, as I understand it, and hope someone can correct that idea if untrue.

Now I also see this drift in my SkySafari app. I'll align to say the Sun, align the app it, and over time, SkySafari will show the scope point well away from the Sun, even though it is still in my camera view?

I would really like to get another CG5 that are on sale right now, because I can use the tripod on this older mount head, and put the new mount head on my pier. I want to do limited AP, mostly video. My expectations for this mount were up to 2 min exposures, and hopefully w/o guiding. This issue however with this CG5, and not able to even to a few seconds without seeing drift, is really pushing me away.

Any ideas on what the issue is??

John


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mclewis1
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Reged: 02/25/06

Loc: New Brunswick, Canada
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5761007 - 03/27/13 06:29 PM

John,

95% of the time it will be your polar alignment. Video cameras with their smaller fov and corresponding "high power" do make tracking inaccuracies quite visible.

If you can verify that your polar alignment isn't causing the problem then look at things like tight clutches. Changing the balance of the scope can sometimes highlight a clutch issue.

Any idea which direction the drift is in? This will tell you what specific areas of the mount to start looking at.


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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
Re: CG5 seems to drift, not steady tracking at all new [Re: mclewis1]
      #5761039 - 03/27/13 06:53 PM

I'll try to determine the drift direction tonight Mark, its actually clear, and with a full moon, a good time to mess with this stuff.

thanks for the suggestions.

John


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rmollise
Postmaster
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Reged: 07/06/07

Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5761933 - 03/28/13 08:54 AM

Why do you think it's not polar alignment? How did you polar align?

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hottr6
Carpal Tunnel
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Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5762205 - 03/28/13 11:11 AM

RU using fresh batteries?

My CG5-clone tracking "slows down" when the batteries get weak. The mount will track in RA for a few more hours then quit all together, and also will not slew. However, the DEC axis will still slew!


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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
Re: CG5 seems to drift, not steady tracking at all new [Re: hottr6]
      #5762607 - 03/28/13 03:33 PM

Clouds rolled in last night, so I couldn't do much to determine direction of drift.

Unc...I used the ASPA. It selected Jupiter, then I adjusted the mount physically.

Hottr6...I have it on a pier and with AC power all the time.

I'll have to wait for my next round of clear skies to determine the direction of drift. From what I recall, it seemed to be in a single direct.

John


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mclewis1
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Reged: 02/25/06

Loc: New Brunswick, Canada
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5762872 - 03/28/13 06:18 PM

John,

ASPA selected Jupiter ... really?

I would use a suitable named star ... suitable would be close to celestial equator and high in the sky but not right on the meridian.


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RTLR 12
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Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CG5 seems to drift, not steady tracking at all new [Re: mclewis1]
      #5762905 - 03/28/13 06:32 PM

Jupiter was selected because that was the last goto that was selected in the HC. Best to use a star close to the meridian and the celestial horizon.

Stan


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rmollise
Postmaster
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Reged: 07/06/07

Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5762910 - 03/28/13 06:33 PM

Quote:

Clouds rolled in last night, so I couldn't do much to determine direction of drift.

Unc...I used the ASPA. It selected Jupiter, then I adjusted the mount physically.

Hottr6...I have it on a pier and with AC power all the time.

I'll have to wait for my next round of clear skies to determine the direction of drift. From what I recall, it seemed to be in a single direct.

John




I would not advise selecting Jupiter for a polar alignment...


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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
Re: CG5 seems to drift, not steady tracking at all new [Re: rmollise]
      #5765654 - 03/29/13 08:11 PM

I'll try the actual stars than next time its clear Unc.

John


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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5766170 - 03/30/13 05:18 AM

Whilst we use drift in dec to set the polar alignment it doesn't follow that the drift is only in dec. It can be in Ra as well. It depends on the direction the scope is pointing relative to the polar align error.

Chris


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Patrick
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5766307 - 03/30/13 08:53 AM

Quote:

My expectations for this mount were up to 2 min exposures, and hopefully w/o guiding.




Hi John,

Are you planning on using your 8" SCT as the imaging scope? If so, I think your expectations may be a little too high. I've had several (3) CG-5's and found through experimentation that the best I could do consistently unguided were 1 minute exposures at a focal length around 300mm. Since you're operating at 2000mm (or ~1260 with an f/6.3 focal reducer), you're going to start to see periodic error problems with even short exposures.

With guiding, the numbers can be much better, although I found that even with a C6 operating at 960mm f/l I had to throw out quite a few subs (approx 30%). The problem you face with guiding with an 8" SCT is that you'll need a second scope which adds to the weight placed on the CG-5. If you operate with a focal reducer (highly recommended) you can probably get away with a 9x50 finderscope guide scope setup. Otherwise, at 2000mm f/l you will want a guide scope with a little longer focal length.

I agree with the others that you need to make sure you have a good polar alignment, but I don't think that's your main problem...yet. I say 'yet', because once you get your periodic error sorted out, that will be the next issue to tackle.

Patrick


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CG5 seems to drift, not steady tracking at all new [Re: Patrick]
      #5766778 - 03/30/13 12:20 PM

yes, 2 min is too much to ask, expect more like 1 min unguided at around 1000 mm focal lenght, IF and only IF you are well polar aligned, your mount is well balanced AND you have a good power supply.

Even with that, GOTO mounts can be misleading somehow: a cg5 that has been correctly put in station, but barely polar aligned, will have good, sometimes even very good GOTOs, which might let you believe that your polar alignement is good too. That is why people in this forum endelessly repeat that polar alignement and GOTOs accuracy are separate things.

Nobody has ever quantified the thing, that is, how far off the north polar pole can you be and still get good GOTOs?
My guess is you can probably be 1 degre off the north celestial pole and still have good GOTOs, but your tracking, while OK visually, will be horrible on a ccd.

The sure thing is that without good GOTOs, you can't expect to have an accurate POLAR ALIGN routine.
So i will say like others: check your battery, balance well in RA and Dec, then do a 2 or 3 STAR ALIGN, stay away from the Meridian and then test you goto accuracy with stars or objects away from the meridian. Only then attempt a POLAR ALIGN routine.
NOTE here: the polar align routine of the cg5 originally used Polaris and was different of the cgem-related ASPA routine. But now you can have both for the cg5.
Which one is best, or lets say 'safer' (as opposed to 'easyer') for a cg5? I don't know.

I would say anyway that if your polar alignment routine shows a big error in alignment, you are probably safer to iterate the entire process once more.


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rmollise
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Reged: 07/06/07

Re: CG5 seems to drift, not steady tracking at all new [Re: dickbill]
      #5766859 - 03/30/13 01:13 PM

Quantify? OK. One night at the club dark site one of our members, Joe Novice we'll call him here, came over to ask for Unk's help. He'd got his new C8/CG5 setup OK, but he was having a problem: "Unk, the go-tos are great, but everything drifts out of my eyepiece." Turned out he'd "polar aligned" on Kochab...

Edited by rmollise (03/30/13 01:14 PM)


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mclewis1
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Reged: 02/25/06

Loc: New Brunswick, Canada
Re: CG5 seems to drift, not steady tracking at all new [Re: dickbill]
      #5767158 - 03/30/13 04:52 PM

Quote:

NOTE here: the polar align routine of the cg5 originally used Polaris and was different of the cgem-related ASPA routine. But now you can have both for the cg5.
Which one is best, or lets say 'safer' (as opposed to 'easyer') for a cg5? I don't know.



A minor point that is really semantics ... ASPA isn't related, oriented or in anyway specific to the CGEM. It was released in firmware gem4.15 which was common across the CG-5, CGE, and the then new CGEM (the CGEPro hadn't been released at that time). There's nothing about ASPA on the CGEM that's any better or worse than on the CG-5 (other than the mechanicals of the mounts being less or more accurate).


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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: CG5 seems to drift, not steady tracking at all new [Re: mclewis1]
      #5767177 - 03/30/13 05:05 PM

An alt az mounted scope can be up to 90 degrees off being polar aligned and still do gotos accurately. The conversion, after a two star alignment, is the same. The difference is that the AltAz mount tracks in both axes while the polar aligned scope tracks in hour angle only.

Chris


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rmollise
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Reged: 07/06/07

Re: CG5 seems to drift, not steady tracking at all new [Re: cn register 5]
      #5767221 - 03/30/13 05:32 PM

That's true, but _it depends on the software_ quite a few GEMs' go-to accuracy ain't worth pea-turkey without a good polar alignment...

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SkipW
sage


Reged: 02/03/11

Loc: Oklahoma, USA
Re: CG5 seems to drift, not steady tracking at all new [Re: cn register 5]
      #5767842 - 03/30/13 11:12 PM

Quote:

Whilst we use drift in dec to set the polar alignment it doesn't follow that the drift is only in dec. It can be in Ra as well. It depends on the direction the scope is pointing relative to the polar align error.


This is true, but with small alignment errors (a degree or two) the drift in RA is so small it's typically swamped by other errors, so we don't notice it.

Drift in Dec is order sin(alignment error).
Drift in RA is order 1-cos(alignment error)

sin(1 degree) is about 0.01745 (1.7%). cos(1 degree) is about 0.9998, so 1-cos(1 degree) is about 0.0002 (0.02%), about 100 times less.

If the alignment error is 90 degrees, the drift in RA (sin(90) = 1) could be as large as the drift in dec (cos(90) = 0, so 1-cos(90) = 1)!

If we're pointing to the wrong pole (error is 180 degrees), all the drift is in RA.

Edited by SkipW (03/30/13 11:14 PM)


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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
Re: CG5 seems to drift, not steady tracking at all new [Re: SkipW]
      #5767965 - 03/31/13 12:43 AM

Still clouds, so further clarification to which direction is taking longer. But I'll keep you all in the loop.

John


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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5771353 - 04/01/13 05:52 PM

Ok, from what SkySafari shows today when broadcasting on NSN, the drift is in BOTH RA and Dec. That REALLY surprises me. When a GEM, the only motor used during normal tracking is RA isn't it? now if SkySafari shows drift in both, that may mean my DEC is off as far as polar goes perhaps?

I'm thus open to suggestions? Oh, and tonight I plan on doing an ASPA on something OTHER then Jupiter, so I'll test again tonight and post up the results.

John

PS. I pulled the trigger on another CG5 since they are on sale. I needed a mount for outreach that I can setup 2 scopes on, so I'll use the new tripod on this older mount head I have, and put the new head on my pier for my AP and broadcasting.


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rmollise
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Reged: 07/06/07

Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5771363 - 04/01/13 05:57 PM

What do you mean by SkySafari showing that it drifts? What happens with an object in the eyepiece at high power?

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WadeH237
Pooh-Bah


Reged: 02/24/07

Loc: Snohomish, WA
Re: CG5 seems to drift, not steady tracking at all new [Re: dickbill]
      #5771489 - 04/01/13 07:09 PM

Quote:

Nobody has ever quantified the thing, that is, how far off the north polar pole can you be and still get good GOTOs?
My guess is you can probably be 1 degre off the north celestial pole and still have good GOTOs, but your tracking, while OK visually, will be horrible on a ccd.




Speaking for the CG5 (and other NexStar mounts), I believe that goto is independent of polar alignment. For quick and dirty visual observing, I frequently just plop the mount down aligned somewhat north and eyeballed level (I do have my latitude dialed in on the mount). Certainly, I am way outside of your arbitrary 1 degree guess. After doing this, gotos work fine and the tracking is "good enough" for casual visual observing.

As Uncle Rod mentioned in another post on this thread, results could vary with another mount. My Astro-Physics mount, for example, syncs to just one star and assumes that the mount is well aligned to the pole. In that case, gotos are quite dependent on polar alignment.

-Wade


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dickbill
scholastic sledgehammer


Reged: 09/30/08

Re: CG5 seems to drift, not steady tracking at all new [Re: WadeH237]
      #5771696 - 04/01/13 09:05 PM

Align on Kochab, almost 26 degres away from Polaris! and still get good GOTOs....wow.
I'd say to John, if you can't see Polaris, or be sure it is Polaris, use your elevation/latitude and a compass and be done with it.
If everything fails (broken gears etc), next step will be Ed Thomas or a new mount i guess. I'd take this as an excuse, like...'Oh, my cg5 is broken, I ABSOLUTELY need a VX...'
Quick! before the money got wasted in who knows what useless item.


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DaveJ
Carpal Tunnel
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Reged: 01/07/05

Loc: NE Ohio
Re: CG5 seems to drift, not steady tracking at all new [Re: dickbill]
      #5771710 - 04/01/13 09:15 PM

Quote:

Align on Kochab, almost 26 degres away from Polaris! and still get good GOTOs....wow.




Well, actually Kochab is 16.6° away from Polaris and 15.8° away from the NCP.

Edited by DaveJ (04/01/13 09:15 PM)


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

Loc: NE Ohio
Re: CG5 seems to drift, not steady tracking at all new [Re: DaveJ]
      #5771726 - 04/01/13 09:28 PM

Quote:

Quote:

Align on Kochab, almost 26 degres away from Polaris! and still get good GOTOs....wow.




Well, actually Kochab is 16.6° away from Polaris and 15.8° away from the NCP.




While I do approve of the good goto accuracy Celestron's combination of alignment and calibration stars can achieve even with a really bad polar alignment, I feel that I must comment that they are just catching up with what the Vixen Sky Sensor 2000 did very well twenty years ago. The SS2K could also correct the declination drift caused by poor polar alignment so the issue discussed in this thread wouldn't be there. ASPA works just like the SS2K polar alignment routine did, also.


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Patrick
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: CG5 seems to drift, not steady tracking at all new [Re: jrcrilly]
      #5771779 - 04/01/13 09:51 PM

Quote:

While I do approve of the good goto accuracy Celestron's combination of alignment and calibration stars can achieve even with a really bad polar alignment, I feel that I must comment that they are just catching up with what the Vixen Sky Sensor 2000 did very well twenty years ago. The SS2K could also correct the declination drift caused by poor polar alignment so the issue discussed in this thread wouldn't be there. ASPA works just like the SS2K polar alignment routine did, also.




Did you ever sell your SS2K?

Patrick


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jrcrillyAdministrator
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Reged: 04/30/03

Loc: NE Ohio
Re: CG5 seems to drift, not steady tracking at all new [Re: Patrick]
      #5771806 - 04/01/13 10:05 PM

Quote:

Did you ever sell your SS2K?

Patrick




I think that set did sell during a weak moment a few years ago but my enthusiasm has returned so I'll be adding more to the collection rather than permitting any more to escape. I still have enough sets for my current projects - an SP, an Atlas, and (my favorite) an old and rare Vixen Sensor (like a GPDX on steroids). I still need to fabricate motor brackets for the Sensor.

BTW - just so folks don't think my comments are completely off topic, the SS2K is the goto system Celestron offered with the CG5 some years before the Nexstar was applied to that mount.


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geminijk
scholastic sledgehammer


Reged: 04/03/08

Loc: TN
Re: CG5 seems to drift, not steady tracking at all new [Re: jrcrilly]
      #5771888 - 04/01/13 10:37 PM

Unc, I was imaging the sun today, and using remote connection to skysafari. That program shows my RA and my Dec moving, even though I"m locked on the target on screen. As I watch the SkySafari program, the reticle indicating my scope gradually moves off target, but not an exact match to what I actually see from my camera, what I mean is it takes longer for me to see the moment on my computer screen of my image, rather then what is showing on my telescope control app.

I also enabled on SkySafari screen RA and DEC lines to determine drift, but it seemed equal in both axis. Speaking of on screen, I do see the movement on my actual program while viewing the Sun disk, takes about 10 or so minutes at least with my DMK and SolarMax. And as luck would have it, clouds rolled in just at dusk.

So I thought it would be some important information from SkySafari, but perhaps not.

So, back to waiting for a clear NIGHT to:
1. do a 2 star alignment and 3-4 calibration stars.
2. Initiate the ASPA routine, and pick a star this time.
3. Test the results of drift and report them hear.

John


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pjensen
super member


Reged: 04/08/12

Loc: Highland Village, Tx
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5771986 - 04/01/13 11:55 PM

FWIW, I was having problems with goto accuracy on my Edge 8 with a CG5. Struggled with it several times last summer and was ready to buy another mount.

This last weekend, I swapped out the finder with a Telrad and put in a polar alignment scope.

What a difference that made. Many times the alignment stars would not be visible in the finder - and I would slew around looking for it (trying to get it in the finder). With the telrad, it is easy to see the star and know which button to push on the controller.

Once I got the polar scope aligned with the mount and the mount aligned with the NCP, the goto's really got spot on. That was after a 2 star alignment with the additional 4 calibration stars.

Did the sky tour and had several nebula show up dead center in the eye piece. It was my best night out ever with the scope.


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Dan Finnerty
sage


Reged: 09/11/11

Loc: Pasadena, CA
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5772000 - 04/02/13 12:05 AM

Quote:


So, back to waiting for a clear NIGHT to:
1. do a 2 star alignment and 3-4 calibration stars.
2. Initiate the ASPA routine, and pick a star this time.
3. Test the results of drift and report them hear.

John




Well, here I go again dropping in to the middle of an ongoing thread without doing all my "homework"...

From your statement above, it appears you are not redoing your alignment after executing the ASPA routine. If you performed the ASAP routine, and properly centered the selected star by moving the Azimuth and Elevation adjustments (*not* by using your hand controller buttons), then you need to remodel. You have physically moved the mount's axes relative to the earth's rotational axis. The mount software does not know how much you actually moved things, so you need to redo the 2-star alignment/x-star calibration to build a new alignment model.

I don't know recall how it works on the CG5 mount, but my C11/G2 will erase the previous model and force a remodel. If you are not redoing the 2-star/4-star modeling, then the mount will be even more confused as to its true position. It may or may not track better depening on how accurately you corrected the alignment, but GOTOs will not be accurate.

I don't get why SkySafari would show any motion. It thinks the mount is properly aligned and is properly tracking on the selected target. It does not know about polar axis misalignment. Of course, that assumes you have selected an object in SkySafari. Hit the Center button at the bottom of the screen and it will move the selected target to the center of the screen surrounded by pulsing cross-hairs.

Depending on how you have SkySafari settings configured, either the object will remain centered on the screen and the coordinates/horizon will move as the earth rotates, or the object will move across the screen as the earth rotates. But the seleted object will stay selected. The cross-hairs will not drift in ra/dec on the screen.

Am I making any sense?

Edited by Dan Finnerty (04/02/13 12:09 AM)


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Dan Finnerty
sage


Reged: 09/11/11

Loc: Pasadena, CA
Re: CG5 seems to drift, not steady tracking at all new [Re: pjensen]
      #5772015 - 04/02/13 12:17 AM

Quote:

FWIW, I was having problems with goto accuracy on my Edge 8 with a CG5. Struggled with it several times last summer and was ready to buy another mount.

This last weekend, I swapped out the finder with a Telrad and put in a polar alignment scope.

What a difference that made. Many times the alignment stars would not be visible in the finder - and I would slew around looking for it (trying to get it in the finder). With the telrad, it is easy to see the star and know which button to push on the controller.

Once I got the polar scope aligned with the mount and the mount aligned with the NCP, the goto's really got spot on. That was after a 2 star alignment with the additional 4 calibration stars.

Did the sky tour and had several nebula show up dead center in the eye piece. It was my best night out ever with the scope.




Boy, is this a familiar story. Mis-identifying an alignment star is the kiss of death. I've torn my hair out and waken the neighbors swearing at the mount for behaving eratically after alignments. Finally it dawned on me (well not quite literally ) what might be happening. Particularly with a straight-through (inverted image) finder it is easy to get confused which star you are centering on, especially if there is a fairly large initial error with the first alignment star. I can see how a Telrad would really help in this situation. I've learned to choose the first few stars carefully to select stars of obvious color/brightness/location that cannot be easily confused. Once the model "tightens up" and pointing accuracy improves, it is easier to look in the finder to see which star the software is trying to point to.


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WadeH237
Pooh-Bah


Reged: 02/24/07

Loc: Snohomish, WA
Re: CG5 seems to drift, not steady tracking at all new [Re: Dan Finnerty]
      #5772042 - 04/02/13 12:44 AM

Quote:

I don't get why SkySafari would show any motion. It thinks the mount is properly aligned and is properly tracking on the selected target.




I think that this is half true. The mount "knows" that its polar alignment is not correct, and by how much. This is how ASPA is able to work in the first place.

If Sky Safari is periodically querying the mount for its position, it will get the place where the mount is actually pointed, including the effect of polar misalignment. Because of this, Sky Safari will show the mount drifting.

-Wade


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Patrick
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5772045 - 04/02/13 12:47 AM

Quote:

1. do a 2 star alignment and 3-4 calibration stars.
2. Initiate the ASPA routine, and pick a star this time.
3. Test the results of drift and report them hear.




As Dan noted, using ASPA will knock your goto alignment off and you will need to do a Re-Alignment (see page 21 of the CGEM User Manual) or power down and redo your goto alignment from scratch.

If I'm short on time, I'll just do a Re-Alignment by slewing to a few alignment stars and hitting the 'Align...Alignment Stars' button and then start replacing alignment stars (that's the Re-Alignment function talked about in the manual).

The routine I prefer when time is not an issue is to do a 2+2 goto alignment with the last star selected being the one I'll use for ASPA. Then I'll run ASPA followed with a 2+4 goto alignment. AFter that I'll check the polar alignment to see how far it's off using the polar alignment star I used previously.


Patrick


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bunyon
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Reged: 10/23/10

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Re: CG5 seems to drift, not steady tracking at all new [Re: Patrick]
      #5772350 - 04/02/13 08:51 AM

There is a very good chance I don't understand how ASPA and 2+4 works but, if ASPA gets the RA axis lined up correctly and accurately, wouldn't tracking be fine, regardless of how the accurate or non-existent the model is?

That is, do mounts that use Nexstar track by turning about the RA axis or do they try to compensate in Dec as well? If the former, what does it matter (for tracking) how accurate the goto model is?


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cn register 5
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Re: CG5 seems to drift, not steady tracking at all new [Re: Patrick]
      #5772356 - 04/02/13 08:55 AM

It is NOT necessary to redo the alignment after an ASPA. The ASPA rotates the align model by the amount of the polar align error.

It is necessary with crude align on Polaris methods because they don't do this but Celestron's ASPA does not require a realign.

But if you enjoy aligning scopes don't let me stop you. Do all the alignments you want.

Chris


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rmollise
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Re: CG5 seems to drift, not steady tracking at all new [Re: jrcrilly]
      #5772359 - 04/02/13 08:56 AM

Quote:


While I do approve of the good goto accuracy Celestron's combination of alignment and calibration stars can achieve even with a really bad polar alignment, I feel that I must comment that they are just catching up with what the Vixen Sky Sensor 2000 did very well twenty years ago. The SS2K could also correct the declination drift caused by poor polar alignment so the issue discussed in this thread wouldn't be there. ASPA works just like the SS2K polar alignment routine did, also.




The declimation drive ideas is fine for visual use BUT it is one of the main things that's stopped me from buying one of their new Starbook mounts, and is why many imagers with them have converted the mounts to use the NexStar HC. As implemented in the Sphinxes it is a killer for imaging.


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rmollise
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Re: CG5 seems to drift, not steady tracking at all new [Re: geminijk]
      #5772369 - 04/02/13 09:02 AM

Quote:

Unc, I was imaging the sun today, and using remote connection to skysafari. That program shows my RA and my Dec moving, even though I"m locked on the target on screen. As I watch the SkySafari program, the reticle indicating my scope gradually moves off target, but not an exact match to what I actually see from my camera, what I mean is it takes longer for me to see the moment on my computer screen of my image, rather then what is showing on my telescope control app.

I also enabled on SkySafari screen RA and DEC lines to determine drift, but it seemed equal in both axis. Speaking of on screen, I do see the movement on my actual program while viewing the Sun disk, takes about 10 or so minutes at least with my DMK and SolarMax. And as luck would have it, clouds rolled in just at dusk.

So I thought it would be some important information from SkySafari, but perhaps not.

So, back to waiting for a clear NIGHT to:
1. do a 2 star alignment and 3-4 calibration stars.
2. Initiate the ASPA routine, and pick a star this time.
3. Test the results of drift and report them hear.

John




I would not worry overmuch about what you see on the SkySafari screen. Get out, do a good polar alignment with AllStar (use a star near the intersection of the Celestial Equator and Meridian) and give it a try under the night sky.


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jrcrillyAdministrator
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Re: CG5 seems to drift, not steady tracking at all new [Re: bunyon]
      #5772390 - 04/02/13 09:11 AM

Quote:

That is, do mounts that use Nexstar track by turning about the RA axis or do they try to compensate in Dec as well? If the former, what does it matter (for tracking) how accurate the goto model is?




Tracking is only in RA and is dependent on polar alignment. ASPA is dependent on the accuracy of the goto model. That's why the goto model is critical for tracking.


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bunyon
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Re: CG5 seems to drift, not steady tracking at all new [Re: jrcrilly]
      #5772413 - 04/02/13 09:22 AM

Quote:

Quote:

That is, do mounts that use Nexstar track by turning about the RA axis or do they try to compensate in Dec as well? If the former, what does it matter (for tracking) how accurate the goto model is?




Tracking is only in RA and is dependent on polar alignment. ASPA is dependent on the accuracy of the goto model. That's why the goto model is critical for tracking.




Okay, I get that. But why would you need to do a remodel AFTER ASPA? I think it was answered above but I want to be sure. If ASPA gets the axis lined up, that should be it.


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jrcrillyAdministrator
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Re: CG5 seems to drift, not steady tracking at all new [Re: bunyon]
      #5772455 - 04/02/13 09:47 AM

Quote:

why would you need to do a remodel AFTER ASPA?




I don't know; I never had to. If everything goes well the first time, there's no reason that it should be necessary.


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Footbag
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Re: CG5 seems to drift, not steady tracking at all new [Re: jrcrilly]
      #5772465 - 04/02/13 09:57 AM

I always powered down after ASPA and then re calibrated on the stars. I think it says to in the manual. This was with a wedge mounted CPC, but I dont see the gems being different.

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WadeH237
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Reged: 02/24/07

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Re: CG5 seems to drift, not steady tracking at all new [Re: Footbag]
      #5772509 - 04/02/13 10:17 AM

On my CGE and CG5s, the ASPA with recent versions of the NexStar firmware do not require you to redo the 2+4 alignment. I vaguely seem to remember that when ASPA first appeared in the firmware, you may have needed to do this.

Some people still redo the 2+4 anyway. I've tried it both ways, and get good results either way. Since it's easier to not re-align, and there is no improvement in results, I don't.

-Wade

PS: If you choose to power down and redo the goto alignment, you only need to do the 2 star alignment. There is no need to redo the 4 star calibration unless you have removed/reinstalled/changed the OTA.


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dickbill
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Reged: 09/30/08

Re: CG5 seems to drift, not steady tracking at all new [Re: DaveJ]
      #5772552 - 04/02/13 10:37 AM

Quote:

Quote:

Align on Kochab, almost 26 degres away from Polaris! and still get good GOTOs....wow.




Well, actually Kochab is 16.6° away from Polaris and 15.8° away from the NCP.




Hmm? isn't it just Dec(Polaris)-Dec(Kochab)=~ 90-74 degres?


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rmollise
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Re: CG5 seems to drift, not steady tracking at all new [Re: bunyon]
      #5772578 - 04/02/13 10:50 AM

Quote:

Quote:

Quote:

That is, do mounts that use Nexstar track by turning about the RA axis or do they try to compensate in Dec as well? If the former, what does it matter (for tracking) how accurate the goto model is?




Tracking is only in RA and is dependent on polar alignment. ASPA is dependent on the accuracy of the goto model. That's why the goto model is critical for tracking.




Okay, I get that. But why would you need to do a remodel AFTER ASPA? I think it was answered above but I want to be sure. If ASPA gets the axis lined up, that should be it.




Why? Because during polar alignment you physically moved the mount (by adjusting the altitude and azimuth of the RA axis).


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jrcrillyAdministrator
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Re: CG5 seems to drift, not steady tracking at all new [Re: rmollise]
      #5772636 - 04/02/13 11:16 AM

Quote:

Quote:

But why would you need to do a remodel AFTER ASPA? I think it was answered above but I want to be sure. If ASPA gets the axis lined up, that should be it.




Why? Because during polar alignment you physically moved the mount (by adjusting the altitude and azimuth of the RA axis).




Hi, Rod.

It's certainly true that you walk up to an aligned mount and, unknown to the controller, adjust it in azimuth and/or elevation you will have disrupted the alignment. With ASPA, though, you are moving the mount as directed by the controller. The controller knows just what you did - in fact, it is relying on that to preserve the star alignment. Any requirement for realignment after that implies an error somewhere in the process; either inaccurate alignment star centering, inaccurate ASPA star centering, firmware errors, or mechanical slop in the system.


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rmollise
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Re: CG5 seems to drift, not steady tracking at all new [Re: jrcrilly]
      #5773038 - 04/02/13 02:09 PM

That's what some folks say, and I certainly believe you've not had to realign. Celestron doesn't seem awful sure, though... (they say "try it, and if go-tos are off, replace stars") given what's in their instructions regarding AllStar. I've had varying success in not having to do/not having to do another go-to alignment after an AllStar. On my to-do list is doing more experimenting with AllStar this spring. I am lazy and usually just use Celestron's earlier Polaris alignment procedure (in NexRemote).

Edited by rmollise (04/02/13 02:10 PM)


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jrcrillyAdministrator
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Re: CG5 seems to drift, not steady tracking at all new [Re: rmollise]
      #5773055 - 04/02/13 02:16 PM

Quote:

That's what some folks say, and I certainly believe you've not had to realign. Celestron doesn't seem awful sure, though... (they say "try it, and if go-tos are off, replace stars") given what's in their instructions regarding AllStar. I've had varying success in not having to do/not having to do another go-to alignment after an AllStar. On my to-do list is doing more experimenting with AllStar this spring. I am lazy and usually just use Celestron's earlier Polaris alignment procedure (in NexRemote).




The ASPA works quite well on the CGE and no realignment was necessary on the ones I've owned, or on others with which I am familiar locally. It may just be that the Chinese mounts are less precise and permit positioning errors to creep in. I know people with CGEMs; I'll have to ask how it works for them.


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DaveJ
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Re: CG5 seems to drift, not steady tracking at all new [Re: dickbill]
      #5773149 - 04/02/13 03:31 PM

Quote:

Quote:

Quote:

Align on Kochab, almost 26 degres away from Polaris! and still get good GOTOs....wow.




Well, actually Kochab is 16.6° away from Polaris and 15.8° away from the NCP.




Hmm? isn't it just Dec(Polaris)-Dec(Kochab)=~ 90-74 degres?




Ah, exactly. 90 - 74 = 16 NOT 26! (although, the 74° isn't exactly correct, it's actually 74.16° so we have:
90° - 74.16° = 15.84° or rounded to 15.8° as I mentioned in my post above.


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dickbill
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Re: CG5 seems to drift, not steady tracking at all new [Re: DaveJ]
      #5773740 - 04/02/13 07:12 PM

dumb me! mentally i substracted to 100, not 90.


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