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Polar alignment in Celestron CG5

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#1 Jabonet

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Posted 02 July 2020 - 03:50 AM

After struggling with the mount I find it almost impossible to get a sub 5' error in polar alignment. When doing polar alignment the telescope slews to polaris. And I have find no way to do the alignment with a different star.
I have seen videos on doing the polar alignment with a different star but they are not clear on what menus on the hand controller to use. And the user friendliness of the user manual is appalling.
I guess people near the equator or the south hemisphere use a different star.
The other solution is drift alignment which I don't know how to do yet. And don't know if it is any better than polar alignment since you have to loose the mount anyway.
The critical thing is to align in azimuth, aligning in elevation is much easier since you don't need to move the base of the mount.

#2 sg6

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Posted 02 July 2020 - 07:11 AM

What you appear to be saying does not seem right.

Polar alignment is with the polar scope up the center of the RA Axis of the mount, not with the telescope.

 

If the scope is slewing to Polaris I guess that it is attempting to go the a start or initial position to begin the Goto alignment which is not directly related to the Polar alignment. Basically you can Polar Align a mount with no telescope.

 

Cannot open the manual, says corrupted. However I have seen a few previous instances where it seems confusion ablout which alignment is which and they end up merging. Guess the manual mentions "scope" and "alignment" in what is close proximity to each other, so people pick the wrong one.

 

Polar alignment is with the Polar scope in the mount. Goto alignment is with the telescope on the mount. You have to do the Polar alignment first, then the goto alignment.

 

Basic Polar alignment should be along the lines of:

Tripod outside, the leg with the "N" on pointed at Polaris, Level mount by adjusting legs, Set Latitude scale to whereever you are (Add a location).

Adjust Az bolts to do a good first go at directing RA Axiz at Polaris. Will need to loosen and tighten each in turn to get head to rotate.

Should be "in the area" now.

Look through polar scope and hopefully Polaris will be in view.

Adjust Az bolts to center Polaris in horizontal field, tighten bolts to hold.

Adjust Elevation adjustment bolts to put Polaris in center.

Then in steps loosen, move and tighten Az and El adjustment bolts to place Polaris at the correct clock position on the engraved circle. Will need some app/software to determine this as the polar scope flips the image.

 

Some people align with the scope in place, others don't. Adding the scope after could alter the PA fractionally.

 

After that you need a telescope to do the goto alignment which it half reads causes the mount to point the telescope at where it believes Polaris is as a start position.

 

I am half guessing you have simply become confused with the rather similar terms used. Both use a scope and both are termed alignment.

 

Probably need you to add more information, I could be 100% wrong. In which case the above is likely to just add to the problem.



#3 Jabonet

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Posted 02 July 2020 - 08:43 AM

Hi SG6
The polar alignment function on this mount requires an initial alignment. I usually do a 2 star alignment with stars on the east and add 2 extra calibration stars on the west of the meridian. I also put the camera piggyback just to include the weight of it while balancing.
After that the polar alignment function points to where polaris should be and tells you to center polaris without touching the control. Moving only the mount screws.
I have the suspicion that the cone error value is wrongly set and that modifies the polar alingment procedure.
But anyway looks like 5' error in alignment makes the periodic error more prevalent. That should mean that no matter how much more accurate I can point the error will not go away.
For what I want I should be able to get some decent 90 second exposures without loosing too many of the shots. Let's see the next chance I get.
Thanks

#4 mclewis1

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Posted 02 July 2020 - 11:08 AM

Jabonet,

 

What firmware do you have in the hand controller (the Version function under Utilities menu)?



#5 Jabonet

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Posted 02 July 2020 - 02:34 PM

HC:GEM 4.13
MC:5.14 5.14

#6 RTLR 12

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Posted 02 July 2020 - 03:29 PM

This is from a later Celestron manual...


Celestron’s All-Star Polar Alignment allows you to precisely polar align your mount without using Polaris or a polar axis finder This software-assisted polar alignment allows you to choose a convenient star
Prerequisite: The CGX-L must first be aligned with a Two Star, One Star, or Solar System Align.
1 Select a suitable bright star from the NexStar hand control’s database Slew the telescope to the star
2 Press the ALIGN button Select “Polar Align” then “Align Mount” from the list
3 The telescope will then re-slew to the alignment star and ask you to center it in the eyepiece in order to “sync” on the star Press ENTER, center the star with the arrow keys, then press ALIGN to sync on the star
4 Press ENTER and the telescope will slew to the position that the star should be if it were accurately polar-aligned At this point, do not use the hand control to center the star
5 Use the mount’s altitude and azimuth adjustments to center the star in the eyepiece
6 Press the ALIGN button
The mount is now precisely polar aligned You may proceed to use the mount without a new go to alignment

#7 mclewis1

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Posted 02 July 2020 - 10:12 PM

The ASPA or the All Star Polar Alignment was added into the firmware at gem4.15. The OPs 4.13 level hand controller will only have the Polaris based polar alignment routine.

 

Jabonet, It's been a very long time since I tried to polar align my ASGT/CG-5 with the old Polaris based routine. I did a few polar alignments just after I got the mount but I don't remember the actual accuracy. I soon after upgraded the firmware to gem4.15 and later 4.19 which I ran for many years. I've done a few of the All Star polar alignments and in general I found them to be more accurate than the older routine ... but I never measured the difference.

 

Most of my polar alignment work has been done with my permanently mounted CGE (also running 4.19 for many years).

 

In general both the old and newer polar alignment routines do indeed rely on the accuracy of the initial alignments. If I'm going to do a polar alignment I will do as good an initial alignment as I can, and I will always add all 4 calibration stars (so a 2 + 4).



#8 mclewis1

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Posted 02 July 2020 - 10:18 PM

While I generally advocate that most folks not bother to touch their hand controller firmware there are enough obvious benefits in the v4 firmware above 4.15 that I would suggest going  right to the last release level of gem4.22. Information about doing the firmware upgrade can be found on Mike Swanson's website - www.nexstarsite.com



#9 Jabonet

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Posted 03 July 2020 - 01:45 PM

Yep. Definitely the problem is the hand controller firmware. ASPA wasn't available until 4.15 4.13 only has polaris and the equivalent for the south Pole. I will see if I can make the cable to upgrade.
I have the mount on a fixed pier so I hope I will not have to align so often. Only once around each new moon.
Thanks for the info

#10 Michael Covington

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Posted 03 July 2020 - 02:20 PM

5' is the typical accuracy of Celestron All-Star Polar Alignment and is actually quite good alignment.   Drift method alignment is more accurate, but you may not need to be more accurate than 5'.




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