Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Mounts

Pages: 1 | 2 | 3 | (show all)
Cliff Hipsher
Pooh-Bah
***

Reged: 12/31/08

Loc: North Chesterfield, VA
Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5665392 - 02/06/13 02:26 PM

Its real easy.

First you have to align the reticule diagram to line up with the counter weight bar. With the mount in the home or starting position (counter weight bar over the NORTH tripod leg) rotate the polar scope so the 'tail' coming off the center cross is aligned with the counter weight bar.

To do a mechanical polar alignment you get the mount level, rotate the mount in DEC to open the view port, and then you rotate the mount in RA so you can place Polaris and Kocab along the upper edge of the counter weight bar.

Look through the polar scope and use the latitude and azimuth adjustments to place Polaris in the circle.

Return the mount to the home or starting position, turn the power on and do a computer aided alignment.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: Confused about how to properly polar allign a CG-5 new [Re: bunyon]
      #5665446 - 02/06/13 02:53 PM

Quote:

Or use a star near the horizon on the equator.



That would be really bad for elevation adjustment.


Post Extras: Print Post   Remind Me!   Notify Moderator  
mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: Confused about how to properly polar allign a CG-5 new [Re: freestar8n]
      #5665505 - 02/06/13 03:24 PM

Quote:

Quote:

The intersection of the meridian and celestial equator is best, by far, to maximize accuracy in both altitude and azimuth.




You could use a land reference to polar align also. Just polar align well, then aim at some fixed object and turn off the mount. When you set it up again, just orient it so the mount is pointing at that object and adjust in alt/az so it is centered.

Since you are moving the mount in alt/az to do this, the best object would be one on the horizon and meridian. Nothing to do with the equator at all.

The same applies to a star. The mount knows where the star should be at all times - and the speed of the star across the sky isn't relevant since its position is always known accurately.

The sensitivity of the az motion just goes as the cosine of the altitude above the horizon. You have no motion at all at the zenith, and maximum motion - and sensitivity - near the horizon.

To avoid refraction and flexure - go up a bit - maybe 20 degrees.

I use ASPA for imaging at around 40N and higher, and I always use a star down low. With cge and cge-pro. Example images are on the MetaGuide site - typically 15m guided with no field rotation.

Again- in many cases the equator/meridian would work ok. But when people say they have poor accuracy with ASPA, I recommend 2+4 and a star lower down - at least to try. No matter what you do want a star near the meridian - for the same reason you want a star near the horizon.

Frank





I am confused. You say “No matter what you do want a star near the meridian”. Then you say “I always use a star down low”. Doesn’t that imply that you always use a star near the equator and meridian intersection?

It looks like Celstron’s instructions specifically say not to use a star near the Poles. Is that not the case?

“For best results choose a bright alignment star that is near the Meridian, preferably close to the celestial equator. Try to avoid stars that are close to the west/east horizon or directly overhead because they can be more difficult to center using the mount's altitude and azimuth controls. Also stars too near the celestial pole are less accurate than those further away.”

Is the intersection of the Meridian and the Celestial Equator directly overhead?

Edited by mpgxsvcd (02/06/13 03:26 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
bunyon
Post Laureate
*****

Reged: 10/23/10

Loc: Winston-Salem, NC
Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5665518 - 02/06/13 03:30 PM

<i>Is the intersection of the Meridian and the Celestial Equator directly overhead? </i>

At the equator, yes. At 40 N, it is due south, 50 degrees above the horizon.


Post Extras: Print Post   Remind Me!   Notify Moderator  
mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: Confused about how to properly polar allign a CG-5 new [Re: bunyon]
      #5665579 - 02/06/13 04:11 PM

Quote:



My subs are all 30 min ...




Without guiding? At what focal length? 2 minutes would be plenty for me.

I am going to try using the Meridian and Celestial Equator in a few minutes. I have never tried that before. Because of my location at my house I was always forced to use a star near the east horizon or straight up. That was probably my issue.


Post Extras: Print Post   Remind Me!   Notify Moderator  
orion69
scholastic sledgehammer


Reged: 05/09/10

Loc: Croatia
Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5665588 - 02/06/13 04:14 PM

Quote:

Quote:



My subs are all 30 min ...




Without guiding?




With CGEM?
Guiding of course.

Sorry I deleted my post.


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5665602 - 02/06/13 04:24 PM

Quote:

“For best results choose a bright alignment star that is near the Meridian, preferably close to the celestial equator. Try to avoid stars that are close to the west/east horizon or directly overhead because they can be more difficult to center using the mount's altitude and azimuth controls. Also stars too near the celestial pole are less accurate than those further away.”

Is the intersection of the Meridian and the Celestial Equator directly overhead?





Hi-

Now I see the confusion on this issue. The celestial equator only goes overhead at the earth's equator. Anywhere else, and it is tilted above the horizon by 90-latitude. So at 40N it is 50 degrees above the horizon. At 20N it is 70 degrees above the horizon, and you would really lose polar alignment accuracy there, in az. The celestron instructions are fine except for the part about the equator. That will work ok for many people (meridian and equator) but it could cause problems. So I use, and recommend, a star down low and near the meridian.

The fact that the instructions say to avoid a star overhead is a direct indication that they don't really mean to use the equator - since the equator can indeed be way up high for locations where the mount is intended for use - e.g. 20 degrees N.

I am in the middle of a rare, due to weather, imaging session right now - and just did a 2+4/ASPA followed by a 2-star using a star down low and near the meridian.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Confused about how to properly polar allign a CG-5 new [Re: freestar8n]
      #5665625 - 02/06/13 04:38 PM

It may be better to say where to avoid.
Avoid the Zenith. The azimuth adjustment just rotates the star field and doesn't really move the stars.
Avoid the East and West. The Altitude adjustment just rotates the field and doesn't really move the stars.
Even if you are hight to the east or West the Altitude adjustment just moves the stars horizontally and that's the same direction as the altitude adjustment.
That leaves South or North and not too high. This comes down to what Frank said, as usual he's right.

Chris

Edited by cn register 5 (02/06/13 04:56 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: Confused about how to properly polar allign a CG-5 new [Re: cn register 5]
      #5665679 - 02/06/13 05:15 PM

Oh, you forgot to mention to avoid the intersection of the meridian and the celestial equator. When in doubt double check with Patrick Wallace, the author of TPoint, who is unquestionable authority on this subject.

Better yet, check the equations yourself then you will know it from the ultimate authority, spherical geometry.

Edited by Alph (02/06/13 05:22 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Confused about how to properly polar allign a CG-5 new [Re: Alph]
      #5665738 - 02/06/13 05:51 PM

Please stop trying to confuse people.

Post Extras: Print Post   Remind Me!   Notify Moderator  
cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Confused about how to properly polar allign a CG-5 new [Re: Alph]
      #5665739 - 02/06/13 05:52 PM

Please stop trying to confuse people.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: Confused about how to properly polar allign a CG-5 new [Re: cn register 5]
      #5665819 - 02/06/13 06:39 PM

Quote:

Please stop trying to confuse people.



I hear you.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: Confused about how to properly polar allign a CG-5 new [Re: cn register 5]
      #5665824 - 02/06/13 06:43 PM

Quote:

Please stop trying to confuse people.



Oh sorry, you really got confused. You double posted.
I recommend that you check first with Patrick Wallace before making insinuations.


Post Extras: Print Post   Remind Me!   Notify Moderator  
cliffy54
professor emeritus
*****

Reged: 03/14/10

Loc: ma
Re: Confused about how to properly polar allign a CG-5 new [Re: Alph]
      #5665877 - 02/06/13 07:20 PM

You guys sure got me confused, it's like reading one of those Newtonian collimation post.

Post Extras: Print Post   Remind Me!   Notify Moderator  
dr.who
scholastic sledgehammer
*****

Reged: 01/05/12

Re: Confused about how to properly polar allign a CG-5 new [Re: mclewis1]
      #5665908 - 02/06/13 07:41 PM

Quote:

The closer you get with that initial rough or what I called "visual" polar alignment (orienting the tripod and mount and sighting up the bore hole) the less movement of the alt and az controls you'll need to do when performing the ASPA. That means less wear and tear on those adjustment bolts and a faster ASPA procedure.




Thank you. That's what I thought.


Post Extras: Print Post   Remind Me!   Notify Moderator  
orion69
scholastic sledgehammer


Reged: 05/09/10

Loc: Croatia
Re: Confused about how to properly polar allign a CG-5 [Re: cliffy54]
      #5665933 - 02/06/13 07:56 PM

Quote:

You guys sure got me confused, it's like reading one of those Newtonian collimation post.






Just read the manual, you'll be fine.


Post Extras: Print Post   Remind Me!   Notify Moderator  
mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: Confused about how to properly polar allign a CG-5 new [Re: orion69]
      #5666915 - 02/07/13 11:33 AM Attachment (7 downloads)

So I tried this last night. I did my typical polar align with the finder scope. I do this very precisely though. Then I did a 2 star + 4 star align with the 10x crop mode on my camera to make sure that the alignment stars were dead center.

I shot a 4 minute and 16 second sub of the Horse Head. It was blown out even with dark skies and my strongest light pollution filter. However, I thought tracking was acceptable considering I wasn’t guiding and I didn’t do the all-star align or a drift align. This was at an equivalent field of view of a Full Frame camera on a 1600mm scope(2x crop factor + 800mm scope).

I knocked it down to where I wasn’t blowing out the sky at 2 minutes and it still was tracking well. Then I did the all star align with Rigel that was approximately to the south and about 40-50 degrees up.

This time I didn’t have to move the mount much at all. I double checked and it moved Polaris slightly off of the circle in the Polar finder. However, when I tried to image again it actually looked like the Polar alignment was off. Not incredibly so but not as good as it was with just the Polar scope.

I then tried to realign everything again from scratch. I tried to get the Polar alignment as precise as before but it was much harder now that the sun had set and my polar scope is not illuminated.

This time when I tried it my tracking was pretty far off. I was having trouble doing anything more than 1 minute subs.

I guess the moral of the story is if it isn’t broken don’t fix it. If the polar finder gets you the results you need then don’t mess it up trying something else. If you are not getting the results you need then definitely try something else.

Thanks for everyone's help. I learned a lot about what to try when using the finder doesn't work and that happens about half the time.

Single exposure 256 seconds with the full spectrum GF1 - Just Polar Aligned visually with the Polar Finder. No Guiding. It is no replacement for guiding but it works if you can't or won't guide.

Edited by mpgxsvcd (02/07/13 12:47 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5666934 - 02/07/13 11:43 AM Attachment (8 downloads)

Here is a stack of 8 1 minute subs with no guiding or all star aligning.

Edited by mpgxsvcd (02/07/13 11:43 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5674091 - 02/11/13 01:44 PM Attachment (7 downloads)

Here is a single 3 minute exposure without any guiding and without using the all star align. This 8" 800mm F4.0 scope was aligned only using the Polar finder visually.

Edited by mpgxsvcd (02/11/13 01:45 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
mpgxsvcd
Carpal Tunnel


Reged: 12/21/11

Loc: Raleigh, North Carolina
Re: Confused about how to properly polar allign a CG-5 new [Re: mpgxsvcd]
      #5674098 - 02/11/13 01:49 PM Attachment (7 downloads)

I did the all-star alignment immediately after I took the first image and then retook the 3 minute image. It has noticeably more trailing after I did the all-star alignment even though I really did not adjust the mount much during the all star align.

Should you wait a certain amount of time before you do the All Star Polar Align? For example does the amount of off-set of the star in the all star aligning process depend on the total amount of time that the mount is tracking?

If your tracking seems good right after you did the visual Polar Align with the Polar Scope should you wait a certain amount of time before doing the All Star align or can it be done accurately right away?

Edited by mpgxsvcd (02/11/13 01:53 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
21 registered and 41 anonymous users are browsing this forum.

Moderator:  Dave M, richard7, bilgebay 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1494

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics