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Equipment Discussions >> Mounts

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rmollise
Postmaster
*****

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
*****

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
*****

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
Postmaster
*****

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
Refractor wienie no more
*****

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
Postmaster
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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
Post Laureate
*****

Reged: 10/23/10

Loc: Winston-Salem, NC
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
scholastic sledgehammer


Reged: 12/26/12

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
Postmaster
*****

Reged: 07/06/07

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
Postmaster
*****

Reged: 07/06/07

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
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
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
Post Laureate
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Reged: 10/23/10

Loc: Winston-Salem, NC
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
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
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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