John Miele
professor emeritus
Reged: 05/29/05
Posts: 722
Loc: North Alabama
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Is this method really more accurate than simply using the polar scope in the first place and carefully placing polaris in the small circle after you have rotated the polar scope to the correct hour angle/clock angle orientation? That process typically gets me pretty darn close to a good alignment. I guess my question is more of ranking the accuracy of these methods. In terms of accuracy I rank the methods as follows from least to best:
Level 1 - is the Polaris hip shot using compass and level.
level 2 - is a careful polar scope based alignment using the method described above.
Level 3 - is classic drift alignment after performing level 2 alignment.
Where does this iterative alignment method fall in those rankings? Between 2 and 3 or is it equal to 3 or is it no better than 2?
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C11/Atlas Mount/Denk II BV
SV102ED/AT Voyager
DSI IIc, DSI II Pro
ST-80, Mallincam Hyper Plus B/W Video Camera
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HaleBopper
professor emeritus
Reged: 01/14/08
Posts: 541
Loc: Great White North
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From what I have read, from my limited exposure, I think this method rivals the drift method for polar accuracy. It may be just as accurate depending on how many iterations you perfrom.
If I may, I would like to add a fourth level: What about accuracy compared to the polar align routine in the CG5, CGEM, and CGE mounts? What if 2or 3 iterations of the polar routine are performed? Will it make a difference? Anyone?
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8" SCT, AT8IN, Losmandy G11, CG5 mounts
Canon Digital Rebel 400
5, 8, 13, 17, 24mm Orion Stratus
Hyperion 31 mm Aspheric
Axiom 23 mm
Pentax 10 mm XW
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LLEEGE
Running out of Oxygen
Reged: 03/03/05
Posts: 9782
Loc: Cloud-chester,NY
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The CGE polar routine is the same thing. It just selects a star for you.
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"Okay! You draw the straws. I'm-a taking the parachute."
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AlexDJ30
sage
Reged: 09/02/08
Posts: 294
Loc: Monterrey, Mexico
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LLeege:
So for the CG-5 mount should be something like this has an example:
1- Put Polaris on the eyepice center it with a high power eyepice, fire up the cg-5, imput the data.
2- Choose a star (from the example rigel) go to it, center it (thats i am loose here, i supouse center it with the hand controll isnt??) then sync to it...
3- Go to again to polaris, center it on high power eyepice only using manual (no hand controll at all) after center go to again to rigel...
do this 3 to 4 times or more...
Is this right? or i am missing something here ???
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Equipment:
- ETX 125 AT
- C6 ASGT
- WO 66mm SD
- 2.5X ED Barlow, 8-24mm Zoom Eyepice
- Canon EOS Rebel XSi
- Celestron Nextimagen
- Orion Starshoot CCD cam
Edited by AlexDJ30 (12/03/08 12:03 PM)
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LLEEGE
Running out of Oxygen
Reged: 03/03/05
Posts: 9782
Loc: Cloud-chester,NY
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That's about it. But use a IR eyepiece. What I do is after i-2 iterations, I then barlow the IR eyepiece to increase the accuracy.
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"Okay! You draw the straws. I'm-a taking the parachute."
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Dean
Post Laureate
Reged: 12/31/04
Posts: 4967
Loc: Bailey Co Elev 8780 feet
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Quote:
From what I have read, from my limited exposure, I think this method rivals the drift method for polar accuracy. It may be just as accurate depending on how many iterations you perfrom.
One factor that limits the iterative methods accuracy is how orthogonal the scope is. The reason being that it assumes that where the scope is pointing is where the mount is pointing - the bigger the difference the less accurate it is. Drift aligning doesn't make this assumption.
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"Don't sweat the petty things and don't pet the sweaty things" - George Carlin
deanrowe.net/astro
Whats with that avatar?
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AlexDJ30
sage
Reged: 09/02/08
Posts: 294
Loc: Monterrey, Mexico
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LLEGE i already have a IR eyepice (12m illumitaned one) is this sufficient or i whould use my 2.5 barlow with it after 2 times or 3 to get more accuracy???.
Now let say i do this, what happen if i add calibrating stars after this method? should i loose accuracy? or will be better?..because the CG-5 you add calibrating stars, so my question is, after doing this is recomeneded add calibrating stars or should i not do it?
This sounds more easy than drift of course i think the first time i would get it in 30 minutes, but with practice maybe in 15 minutes your inn.
Thanx for the info!
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Equipment:
- ETX 125 AT
- C6 ASGT
- WO 66mm SD
- 2.5X ED Barlow, 8-24mm Zoom Eyepice
- Canon EOS Rebel XSi
- Celestron Nextimagen
- Orion Starshoot CCD cam
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Skylook123
Postmaster
Reged: 04/30/05
Posts: 5254
Loc: Tucson, AZ
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Quote:
Quote:
From what I have read, from my limited exposure, I think this method rivals the drift method for polar accuracy. It may be just as accurate depending on how many iterations you perfrom.
One factor that limits the iterative methods accuracy is how orthogonal the scope is. The reason being that it assumes that where the scope is pointing is where the mount is pointing - the bigger the difference the less accurate it is. Drift aligning doesn't make this assumption.
Very true. Any cone error would cause a non-covergence, as well as changing an eyepiece or even changing focus on an SCT with mirror shift. So would not having a reticle eyepiece for a consistent reference.
My experience is with a 10" SCT at 2500mm, using an 8mm plossl without a reticle for alignments. If I defocus to get a fatter image, the main limit to fast polar alignment is precision on the leveling, compass, and latitude setting of the mount head with compass alignment being my Achilles' heel. As I've said a few times so far, for my visual work all I usually need is one hop and I can get Polaris into the polar scope, and use the HC polar angle to finsh adjusting. But there have been times when I'm in too much of a hurry, and that causes me to either spend a whole lot more time on it, or having awful tracking for the public guests. If I someday buy a reticle eyepiece I'll rule the world! 
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Jim
A Bad Night With A Telescope
Beats A Good Night Doing Anything Else
Teeter 18" Truss Dob/Sky Commander DSCs, "Derrick"
Meade 10" LX-5 SCT/Atlas-G "Ol' Blue Eye"
Orion 90mm refractor,
Meade 10" Starfinder Newt/JMI NGCMax DSCs,
Celestron 10x50 Ultima Pro
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LLEEGE
Running out of Oxygen
Reged: 03/03/05
Posts: 9782
Loc: Cloud-chester,NY
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Quote:
LLEGE i already have a IR eyepice (12m illumitaned one) is this sufficient or i whould use my 2.5 barlow with it after 2 times or 3 to get more accuracy???.
Now let say i do this, what happen if i add calibrating stars after this method? should i loose accuracy? or will be better?..because the CG-5 you add calibrating stars, so my question is, after doing this is recomeneded add calibrating stars or should i not do it?
This sounds more easy than drift of course i think the first time i would get it in 30 minutes, but with practice maybe in 15 minutes your inn.
Thanx for the info!
Barlowing will help on the final iteration or two. Once you are "Polar" aligned, recalibrating the mounts goto will not hurt. It will, in fact, improve your goto's.
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"Okay! You draw the straws. I'm-a taking the parachute."
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tommyhawk13
professor emeritus
Reged: 09/28/07
Posts: 739
Loc: Jacksonville, Fl
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I use the drift method for a couple of reasons.
1.) I do not have go-to.
2.) I shoot long exposures, up to 40 miniutes, or longer.
By using the drift method, I can visually verify that the star has not drifted in declination for 10 minutes. I don't have to sit at the eyepiece the entire time, I can go inside and get a drink, and come back in an hour, If I want to.
I admit it is frustrating to learn, but it gets easier.
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Meade Starfinder 8,Meade SN-8 OTA, Orion Atlas, and a handfull of film cameras
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Stardaug
professor emeritus
Reged: 08/03/08
Posts: 549
Loc: Ontario, Canada
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So I've been trying this technique out and I'm stumped a bit.
AstroPlanner suggested Rotinev (spelling?) as the best star to use in conjunction with Polaris.
I couldn't get either to center on the cross hair no matter what. Polaris was a lot closer to center though. Rotinev was in the FOV but never got any better in position.
Do you do a rough polar align and then center Polaris using the wedge controls before a goto the Iterative star that you center with the HC and sync on?
I did that, used wedge controls for Polaris centering and the HC for the Iterative star, along with syncing on it prior to a goto back to Polaris. Once Polaris was centered using the wedge controls I unsynced the Iterative star and did a goto back to it repeating everything. But just didn't make any progress beyound a certain point.
Anyone have some suggestions at all?
Thanks!
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"Keep looking up!"
Shawn / Ontario, Canada
Celestron CPC800 SCT w/XLT & GPS // Skywatcher Equinox 80ED F6.25 500mm APO // Canon Rebel 350XT unmodded // Milburn EQ Wedge (a Meade model modified to fit my CPC)
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wsuriano
super member
Reged: 11/13/07
Posts: 105
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Don't center Polaris. Only take up half to 2/3 of the amount you are off in both Dec and RA. Then go back to the other star you are using, sync on it and repeat. Over several iterations, Polaris (actually both stars) should get closer and closer to the center.
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Meade 8" LX90 GPS w/wedge
Meade 5000 80mm APO
Vixen 5" Newtonian
Orion 120mm f/8.3
Orion ST 80mm
Meade ETX90 PE
CGEM
CG-5 ASGT
iOptron MT
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Stardaug
professor emeritus
Reged: 08/03/08
Posts: 549
Loc: Ontario, Canada
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Thanks for the input. I did read about doing half or 2/3 way earlier in this thread. I also read about just centering polaris.
Why would centering Polaris instead of halfway say, cause a problem?
Also, do you start the process by goto Polaris and centering it? To start things off? Or do you goto the Iterative star first?
Thank you!
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"Keep looking up!"
Shawn / Ontario, Canada
Celestron CPC800 SCT w/XLT & GPS // Skywatcher Equinox 80ED F6.25 500mm APO // Canon Rebel 350XT unmodded // Milburn EQ Wedge (a Meade model modified to fit my CPC)
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DeanS
Pooh-Bah
Reged: 07/12/05
Posts: 1152
Loc: Nicholasville, Kentucky
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For those that do iterative, how would you compare it to using the PemPro polar alignment? Which of course is drift using the ccd.
When I set up at star parties I want to have all my gear installed and hooked up before dark. I don't generally ever use an eyepiece and would hate to think I have to put the camera on after this.
Can the iterative be used with a CCD. I would imagine it has to be wide field?
In the AP manual Roland talkes about doing a similar alignment, but does a flip each time going to the same star, and says the finder scope will do a very close job itself.
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AP1200GTO AP900GTO
TOA-150 Tak E160
C9.25 Tak FS60C
SXV-H9 ST2000XM STV
8" LX200GPS
Meade 12" Lightbridge
Moonlite Focusers
www.doghouseastronomy.com
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LLEEGE
Running out of Oxygen
Reged: 03/03/05
Posts: 9782
Loc: Cloud-chester,NY
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Quote:
In the AP manual Roland talkes about doing a similar alignment, but does a flip each time going to the same star, and says the finder scope will do a very close job itself.
I have used his quick drift method at it is fast and easy and you only need a finder.
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"Okay! You draw the straws. I'm-a taking the parachute."
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Bowmoreman
Post Laureate
Reged: 09/11/06
Posts: 4152
Loc: Bolton, MA
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Quote:
Don't center Polaris. Only take up half to 2/3 of the amount you are off in both Dec and RA. Then go back to the other star you are using, sync on it and repeat. Over several iterations, Polaris (actually both stars) should get closer and closer to the center.
Exactly correct... each "return" to Polaris, try to use your alt/az adjustments to move it around 1/2 to 2/3 of the way TO the center...
Then do the GoTo the alignment star again. Dead center it... then goto back to Polaris; again move it 1/2 to 2/3 of the way to centered...
If you are careful, after the first 2-3 iterations, you will need to increase focal length (you can use very short fl IR EP like I do - a 5mm IR, or just use a 2, 2.5, or 4x barlow)...
But, with My MI-250, I found 5 iterations (total) got me to where I have zero field rotation on 15 minute subs at f6.3 on a C11...
(I never used my Barlow, only the 5mm IR EP)...
Sometime when I'm feeling bored on a full-moon night maybe, I'll add in my 2X powermate and do 2-3 more iterations...
The "go only 1/2 to 2/3 of the way to Polaris" each time is important, because otherwise you'll just "thrash" around the exact location (back/forth) w/o knowing for certain that you've approached it consistently...
In this sense the MI-250 (Gemini) approach is fully the same as on my old CGE...
clear enough skies
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Dave
Imaging: MI-250+ADM/SBS/Optec Libra: C11Hyperstar,TMB80SS
Visual: XT10i RTP
EP: 31T5,22T4,17T4,12T4,13Ethos,10XW,8Ethos;2x Powermate,Paracorr, 1.6X Antares, Hyperion8-24Zoom
Cameras: Mallincam Color Hyper Plus, QHY8
Guider: SBIG STV eFinder
Key Add-ons: Gerbings Heated clothes, WilderSkiesObservatory(BYO#90), Speco 9"Monitor
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Stardaug
professor emeritus
Reged: 08/03/08
Posts: 549
Loc: Ontario, Canada
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Dave - thanks for the explanation. Makes sense now. I'm looking forward to experimenting more with it. Especially given your results on 15min subs with the C11/f6.3.
Cheers!
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"Keep looking up!"
Shawn / Ontario, Canada
Celestron CPC800 SCT w/XLT & GPS // Skywatcher Equinox 80ED F6.25 500mm APO // Canon Rebel 350XT unmodded // Milburn EQ Wedge (a Meade model modified to fit my CPC)
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pogobbler
member
Reged: 09/30/08
Posts: 51
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As regards a CG5 go-to mount, I still haven't heard a clear answer as to whether this iterative method is more accurate and/or easier than the built in polar alignment routine. Anyone?...Anyone?
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Skylook123
Postmaster
Reged: 04/30/05
Posts: 5254
Loc: Tucson, AZ
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Iterative can get you close, and that's its main feature; any mount that has a view of Polaris and has GOTO is a candidate to use it. But since it's behavior is of convergence, not absolute accuracy, I've used it best when I have a polar scope to finish the task once I get Polaris into the FOV of the polar scope.
I'm using an Orion Atlas, same Synta mount as a Skywatcher EQ6, and every setup is at a different part of town for schools and other outreach. It is a feature of the Synta software that it plays mischief with acceptable GOTO alignment precision if your polar alignment is not pretty tight. I've probably done the iterative method about 250 to 300 times, and I can verify that if you get impatient and try to take out more than 3/4 of the offset you will be chasing it a long time.
In my experience, two or three iterations and I'm within two degrees; after that, it takes the polar scope markings to bring it in the rest of the way.
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Jim
A Bad Night With A Telescope
Beats A Good Night Doing Anything Else
Teeter 18" Truss Dob/Sky Commander DSCs, "Derrick"
Meade 10" LX-5 SCT/Atlas-G "Ol' Blue Eye"
Orion 90mm refractor,
Meade 10" Starfinder Newt/JMI NGCMax DSCs,
Celestron 10x50 Ultima Pro
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freestar8n
sage
Reged: 10/12/07
Posts: 394
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The cg5 has a built-in polar alignment routine that is easy to use and doesn't require a view of polaris. It takes into account cone and other mount errors as long as the mount has been aligned with calibration stars. It is certainly more efficient than other methods since it is a very direct procedure and you do it once. For my cge it appears to get within about 5' of the pole and lets me do guided imaging directly.
So - based on my cge and the polar align routine, and the fact that it corrects for cone error and such, I don't know why anything else would be used.
Example images after AllStar align are here.
Frank
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