anivision
member
Reged: 05/09/09
Posts: 12
|
|
I'm interrested in how accurate the "all star polar alignment" is on a CG-5. Has anyone done an "all star alignment" and then made for example a drift alignment and then comepared the results?
In other words, is there any need to super tune the alignment after "all star polar alignment"?
Clear skys everyone!
|
LarsZ
super member
Reged: 01/12/08
Posts: 114
Loc: Sweden
|
|
Can't help you with the CG-5 (as you probably know  ) but I have checked with my CGE, and since they use the same handcontrol, the result chould be almost the same.
The only difference I can imagine would be that the CGE may be a little more consistent in the results since it's mechanically more reliable.
I do the all star polar align with 2+3 or 2+4 stars twice with the CGE, though the necessary adjustments the second time are very small.
I have checked the results on 2 occasions with the WCS drift align program.
The first time, I ran the WCS drift align for about 5 minutes in RA and DEC respectively and there was zero correction necessary.
The second time I ran the drift align program almost 10 minutes to make sure I covered a full worm cycle on the CGE (8 minutes). This time the WCS program showed the smallest possible correction in DEC, but I let it pass since I can't make such small adjustments with the CGE.
To make it short, if you do the polar align twice, there should be no advantage to make a drift align afterwards. Actually I think a single 2+4 polar align is good enough also for imaging.
/Lars
--------------------
Rebel XSi, IDAS LPS, CGE 9.25, Orion SSAG, Starblast 4.5
|
gezak22
sage
Reged: 08/15/04
Posts: 206
Loc: Goleta, CA, USA
|
|
I have a CG5-ASGT. Given that you want a comparison to drift aligning, I am assuming that you are planning on imaging. I do piggypack imaging with a 100mm lens and I find that without guiding, 3min is the most I can do. This is after three iterations of 2+4 with 2 polar alignments in between. However, I am not sure if I am selecting the correct stars for the polar alignment.
The Gotos are incredibly accurate.
Unfortunately, I don't have a comparison to drift alignment.
|
anivision
member
Reged: 05/09/09
Posts: 12
|
|
hi Lazze, so I see you here on this forum also  time for the swedes to take on the world
Ok, so the ASPA function is working wery well then. Hopfully it works good enough on a CG5 as well.
|
Alph
sage
Reged: 11/23/06
Posts: 259
Loc: Melmac
|
|
Quote:
I'm interrested in how accurate the "all star polar alignment" is
Someone has just found out that the "all star polar alignment" routine is buggy. Read the message #24756 on the Yahoo CGE group.
|
mclewis1
Thread Killer
Reged: 02/25/06
Posts: 3943
Loc: New Brunswick, Canada
|
|
Quote:
Someone has just found out that the "all star polar alignment" routine is buggy.
"Might be buggy" would be a better term ... there's no confirmation that this is a bug yet.
--------------------
Mark
C11, C6, APM/TMB115, and AT80ED - Tandem mount CGE and CG-5A, WO EZ-Touch and AT Voyager
25x100s and 8x56s, T-Mount Light, Mark 1 eyeballs - Modded 350D, DSI-P, SPC900, Mallincam
Just because you can doesn't necessarily mean that you should
|
Patrick
Postmaster
Reged: 05/16/03
Posts: 7803
Loc: Franklin, Ohio
|
|
Quote:
Someone has just found out that the "all star polar alignment" routine is buggy. Read the message #24756 on the Yahoo CGE group.
If that were the case, I think more people would have been complaining by now. I've used it successfully a number of times on my CG-5. Although I haven't compared it directly to a drift alignment, the lack of field rotation in my images tells me that the polar alignment is very good.
Patrick
--------------------
10" f/6 Truss Tube Newtonian
Celestron C6S-GT SCT
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Celestron Regal 8x42 Binocular
Canon XSi; Meade DSI;SPC900-NC
Vixen GP2 Photo Guider Mount
My Astronomy Pages
|
Alph
sage
Reged: 11/23/06
Posts: 259
Loc: Melmac
|
|
Quote:
If that were the case, I think more people would have been complaining by now
You could think so but most people will not bother to do a simple test to verify somebody's assertion. I did verify it. I suggest you do the same.
|
jog
member
Reged: 10/26/06
Posts: 90
Loc: nj
|
|
buggy or not it works well enough for me.
|
Tim C
sage
Reged: 11/11/07
Posts: 271
Loc: Marietta, GA
|
|
I had a CGEM for a while. My standard for a drift align (right or wrong) was no drift at 300x for 5 minutes. With the all star routine, I would see drift after 2 minutes at 300x and would have to tweak via drift alignment to get it to where I wanted. Of course, the 2 minutes with no drift is plenty good enough I'm sure especially if you are guiding in declination. As a comparison, I upgraded to a Tak EM200 mount and using just the Tak polar scope I get no drift for the 5 minutes at 300X 90% of time.
Tim
--------------------
Tim
Some average astrophotos: http://TCardin.zenfolio.com/p355986048
|
LarsZ
super member
Reged: 01/12/08
Posts: 114
Loc: Sweden
|
|
I did read the thread, and it turns out that during testing, the GoTo when performing the ASPA put the star 4 arcminutes from the GoTo when using the "Named star" routine. The difference was in RA. No difference in Dec.
No outdoor trials or drift aligning after these tests yet, but it would be interesting to see somebody else doing drift aligning after the ASPA. For me it is not that important if a GoTo ends up 4 arcminutes away after a polar align. It is more important that the correct coordinates are used for the polar align.
Still I am curious why such an error did not show up when I tested drift aligning after the ASPA. I have had a very good experience with the WCS drift aligning program.
/Lars
--------------------
Rebel XSi, IDAS LPS, CGE 9.25, Orion SSAG, Starblast 4.5
|
Alph
sage
Reged: 11/23/06
Posts: 259
Loc: Melmac
|
|
Quote:
For me it is not that important if a GoTo ends up 4 arcminutes away after a polar align
I think you have misread the post. The GoTo ends up 4 arcminutes off just before the polar alignment. The sync is done using wrong coordinates.
Quote:
It is more important that the correct coordinates are used for the polar align.
That is what the problem is - the wrong coordinates
|
stevecoe
"Astronomical Tourist"
Reged: 04/24/04
Posts: 2637
Loc: Arizona, USA
|
|
Alph;
Do you mean wrong coordinates within the database in the handpaddle? Are there stars to avoid with my CGEM because the RA and Dec are incorrect?
Lars, you used one too many acronym for me...I got ASPA is the All Star Polar Alignment, but I need some help with WCS.
Clear skies;
Steve Coe
--------------------
TeleVue 102 refractor on CGEM mount
10 inch f/4.7 Newtonian
Author "Deep Sky Observing" Springer-Verlag
Author "Nebulae and How to Observe Them" Springer
Canon Xt astrocamera with Hutech modification
|
LarsZ
super member
Reged: 01/12/08
Posts: 114
Loc: Sweden
|
|
Steve,
Sorry for my abbreviations. Sometimes I just get too lazy....
WCS stands for WebCamScheinern. I'm taking this from my memory now so a grain of salt is requested, but if I remember correctly from the WCS website, Scheiner comes from the 19th century (?) astronomer Julius Scheiner who invented the method of drift aligning.
The web site (and the story behind Mr Scheiner) can be found here: http://wcs.ruthner.at/index-en.php
/Lars
--------------------
Rebel XSi, IDAS LPS, CGE 9.25, Orion SSAG, Starblast 4.5
|
LarsZ
super member
Reged: 01/12/08
Posts: 114
Loc: Sweden
|
|
OK. Thanks for the correction Alph.
Can you or anybody else confirm with real-life data that this indeed puts the polar align 4 arc-minutes off? Sorry for asking, but I really felt I got consistent results when I checked the ASPA afterwards.
/Lars
--------------------
Rebel XSi, IDAS LPS, CGE 9.25, Orion SSAG, Starblast 4.5
|
Alph
sage
Reged: 11/23/06
Posts: 259
Loc: Melmac
|
|
Quote:
Can you or anybody else confirm with real-life data that this indeed puts the polar align 4 arc-minutes off?
It is easy to confirm it. You don’t even have to go out with your mount. You can do it at home. Select a star from the Named Stars list and GOTO it. Tap on UNDO twice. Hit MENU and select Get RA-Dec. Write down the coordinates. Tap on UNDO twice and then on ALIGN. Select Polar Align / Align Mount and press ENTER. The mount will slew again to the star it has slewed last time. Tap on UNDO twice and then on MENU. Select Get RA-Dec. Write down the coordinates and compare with the previous values you wrote down.
|
Alph
sage
Reged: 11/23/06
Posts: 259
Loc: Melmac
|
|
Quote:
Do you mean wrong coordinates within the database in the handpaddle?
No. The coordinates used for a normal GOTO are fine. The coordinates used for a GOTO during the polar alignment routine are off by 16 seconds (4 arc minutes).
|
Chris Rowland
sage
Reged: 02/28/05
Posts: 268
|
|
This is what's happening. It's based on what I've been told by the developer so it isn't speculation.
If you do an AllStar align slew the position the scope arrives at is a bit out in Ra. This is because the hour angle of the destination is determined at the start of the slew rather than at the end, as normally happens. The difference will be proportional to how long it takes to get to the position so if you are close to the align star position it will be small.
THIS MAKES NO DIFFERENCE to the polar align accuracy because you then do a manual sync movement to the actual position of the star. All it means is that the initial slew isn't as accurate as a normal slew so you have slightly further to move the scope than you might otherwise need to do so.
Yes, it's a bug but not a huge one. AllStar polar alignment still works.
Celestron will be informed and I'm sure they will fix it.
Chris
|
LarsZ
super member
Reged: 01/12/08
Posts: 114
Loc: Sweden
|
|
Thanks a lot for your clarification Chris.
/Lars
--------------------
Rebel XSi, IDAS LPS, CGE 9.25, Orion SSAG, Starblast 4.5
|
Alph
sage
Reged: 11/23/06
Posts: 259
Loc: Melmac
|
|
Quote:
If you do an AllStar align slew the position the scope arrives at is a bit out in Ra.
If a GOTO takes 60, 80, or 100 seconds, the RA will be off by 15, 20, or 25 arc minutes respectively . That's a quite big difference. The minimum GOTO time is around 16 seconds which is equivalent to 4 arc minutes.
Quote:
Celestron will be informed and I'm sure they will fix it.
I am glad to hear it. I also would like to be able to use ALIGN from the SAO menu.
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 