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Not able to properly polar align CG4 mount, and not sure what's the cause...

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#1 SalehRam

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Posted 12 February 2019 - 04:54 AM

Hello all!

 

Last night I had a chance to go to a less light polluted sky and setup my telescope. I wanted to take some shots for the nebulas in Orion, however I wasn't able to get a proper polar alignment for the required long exposures...

 

I'm at a latitude of 21.45" North. I wear eyeglasses and I am not the best in spotting stars at sky, so I rely on binoculars to find and spot Polaris and point the tripod in its direction, I have a compass as well but I am starting to doubt its accuracy...

 

I also have the polar finder scope installed (and properly aligned) on the mount and a 8x50 finderscope. All of those I use to find and work on the alignment of the telescope, and with all of those except the polar finder scope I can see Polaris very easily. I am not sure whether the issue is because of the scale of the latitude is not accurate on the mount (so I end up much higher or lower than what I need) or because the magnification of the finder scope is weaker than the other optics I use to show the star, but no matter what I do I cannot see the star through that scope.

 

I would like to know which is not accurate of these: (or start getting things sorted out on what's the inaccurate part in this sequence)

  • Is there any chance that the latitude scale is not accurate or too small (or tight) for it to be accurate and show my correct latitude point? (I know it is divided by 2 degrees, but I'm at 21.45, so I set this roughly a little bit before the 22" mark)
  • Or is it about magnification power and my eyes are not helping? bawling.gif

I'm having some ideas on solving this problem, but those ideas involving a DIY polar alignment camera. I already have a mono QHY5LII camera I use it with a mini-guide scope. And I notice that this camera and the guide scope have a slim body and 1.25" diameter and the camera is sensitive as well. I also happen to have a 3d printer, and the polar finder scope front cap on the mount is round and is hollow, so I can make another role for the guide scope and camera and print a mount and slide it in the polar finder tube and use it as a way to find and align the mount to Polaris. I'm just not sure how that will end up or how effective it will be...

 

Anyone had any experience with such solutions? Or before, with such problems in seeing Polaris? lol.gif

 

Really appreciate your feedback and help! bow.gif


Edited by SalehRam, 12 February 2019 - 04:57 AM.


#2 DuncanM

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Posted 12 February 2019 - 05:07 AM

IIRC, You have to rotate the mount in Dec to allow the polarscope to view the sky.

 

Your mono QHY5LII camera and mini-guide scope can be used with Sharpcap as an electronic polarfinder scope:

 

https://www.sharpcap...polar-alignment



#3 SalehRam

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Posted 12 February 2019 - 05:15 AM

IIRC, You have to rotate the mount in Dec to allow the polarscope to view the sky.

 

Your mono QHY5LII camera and mini-guide scope can be used with Sharpcap as an electronic polarfinder scope:

 

https://www.sharpcap...polar-alignment

That's a CG4 I have, the polar scope is not blocked like in the CG5..

 

And looking at the feature of SharpCap, I'm not sure why I never saw this before... frown.gif

 

I'll be checking this tonight with the sky still clear I hope it will be easy thing to do!

 

Appreciate your help and feedback!



#4 DuncanM

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Posted 12 February 2019 - 05:23 AM

Another tip. If you know where you will setup, you can use google earth to identify a landmark that you will point you due north.



#5 BQ Octantis

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Posted 12 February 2019 - 05:33 AM

Your polar alignment scope is only good enough for visual. As are your built-in level and latitude markings. For AP, you need to either do drift alignment or direct measurement of your polar axis through a camera. If you have a DSLR and a 50mm lens, I wrote a detailed article on how to do the latter here (albeit for the southern celestial pole—out of sheer necessity):

 

https://www.cloudyni...lar-alilgnment/

 

If not, reco you get a Polemaster.

 

BQ


Edited by BQ Octantis, 12 February 2019 - 05:35 AM.

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#6 SalehRam

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Posted 12 February 2019 - 06:31 AM

Well, a PoleMaster is something appeals me, however I thought I do my own and utilize the mini guide scope and camera..

Looking at SharpCap and the polar alignment method it provides I will look at achieving it without changing anything in my setup, then will see the DIY things aa Im a bit DIY oriented.

PoleMaster is a last option :D

#7 KLWalsh

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Posted 12 February 2019 - 08:15 PM

I use my smartphone (iphone 6s+) with the Compass and Carpenter’s Level apps to line up the mount when I set up in the daytime.
I first make sure the mount is vertical, just for ease of alignment. Then the compass app gives me a pretty good true north alignment of the polar axis. Then I set my phone on the dovetail mounting surface and adjust the angle to my latitude.
This gets me really close to the pole; then I tweak the alignment to get Polaris axis centered in the polar scope.

#8 OldManSky

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Posted 13 February 2019 - 11:43 AM

If you're having trouble just getting Polaris into the FOV of your polar scope, which it sounds like you are...

Don't feel bad.  Sometimes it's just not that easy.  Especially for us eyeglass wearers.

 

Here's a simple little aid I came up with years ago that helps get Polaris into your polar scope's FOV:

 

Get a plastic soda straw.  One of the "fat" ones is better than the really skinny ones, but either will work.

Cut off about a 2" - 3" long piece of it.

Tape it to the side of your RA axis so that it's in line with the centerline of the axis.

 

That's it.  You now have a really simple "Polaris finder" that's lined up roughly with your scope's RA axis.  Set up as close to north/latitude as you can in the daytime.  As soon as Polaris is visible, go behind your mount and sight Polaris with both eyes open, then put your head behind the soda straw.  If you can see Polaris inside the straw tube, it'll be in your polar scope's FOV.  If you can't, adjust the mount in alt-az until you can. :)


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#9 macdonjh

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Posted 13 February 2019 - 06:59 PM

If you have a DSLR and a 50mm lens, I wrote a detailed article on how to do the latter here (albeit for the southern celestial pole—out of sheer necessity):

 

https://www.cloudyni...lar-alilgnment/

 

BQ

When you're ready to write an addendum to your article for northern hemisphere use, you can stay at my house during your research time.



#10 BQ Octantis

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Posted 14 February 2019 - 04:44 AM

When you're ready to write an addendum to your article for northern hemisphere use, you can stay at my house during your research time.

Thanks mate! But it'll be some time before I have my setup in the north…

 

BQ



#11 SalehRam

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Posted 14 February 2019 - 05:00 AM

Well I think it will be much easier for me after all these tips and replies! Thanks a lot everyone...

 

I've gone ahead with my plans to do a mount for my small QHY mini guide scope and camera so it can act as a simple polar finder.. I'll  post another topic or reply here with the details and the results once I'm done with this.

 

The mobile level app did help a lot. I took only the mount out last night and tested how I can work with the mobile app and it was much easier to get to an approximate latitude...

 

Still haven't got the straw method to work but I'm planning to go out today with the full setup some time early and fiddle with the whole thing.

 

Appreciate all the input and the feedback that you put here!

Regards



#12 Cancington42

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Posted 17 February 2019 - 06:52 PM

As soon as I started using the polemaster all polar alignment issues when away. It is an invaluable tool that works really well!! Definitely worth looking into! 



#13 SalehRam

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Posted 19 February 2019 - 07:33 AM

As soon as I started using the polemaster all polar alignment issues when away. It is an invaluable tool that works really well!! Definitely worth looking into! 

I've been looking with interest at the PoleMaster but I usually need to convince myself there is no way around before getting it, the other issue is I have a CG4 mount, which is while good, it is still not the best for AP so I'm trying to restrain any investment I do with it to be in a way it will allow for better visual and some limited AP (this limited AP will be pushing the scope and the mount to their max)...

 

So once I get a better place to live, and a better stable situation, a more advanced AP/visual setup is on the list...

 

For now I finished a simple mount I came up with for my MiniGuideScope and QHY5LII mono cam, so they can act as a little/simple polar finder scope to at least point me to the right direction in the sky...

https://photos.app.g...9Apdd4E6raKkuS6

 

Still haven't been able to test it, clouds decided it is a good time to hang over my location and block east/north sky :( ...

 

Regards



#14 DuncanM

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Posted 19 February 2019 - 11:07 AM

I've been looking with interest at the PoleMaster but I usually need to convince myself there is no way around before getting it, the other issue is I have a CG4 mount, which is while good, it is still not the best for AP so I'm trying to restrain any investment I do with it to be in a way it will allow for better visual and some limited AP (this limited AP will be pushing the scope and the mount to their max)...

 

So once I get a better place to live, and a better stable situation, a more advanced AP/visual setup is on the list...

 

For now I finished a simple mount I came up with for my MiniGuideScope and QHY5LII mono cam, so they can act as a little/simple polar finder scope to at least point me to the right direction in the sky...

https://photos.app.g...9Apdd4E6raKkuS6

 

Still haven't been able to test it, clouds decided it is a good time to hang over my location and block east/north sky frown.gif ...

 

Regards

You're now all setup for using Sharpcap via your miniguidescope - probably no need for extra gear at this point.



#15 gnowellsct

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Posted 21 February 2019 - 12:06 AM

The latitude markings on inexpensive mounts (and even expensive ones) are notoriously in accurate.  It's best to set up, level the mount, and align on polaris.  Whatever Polaris says your dec is, that's your Dec.  Maybe it will say 25 maybe it will say 18, but whatever it is, if Polaris is in the polar scope, that's the right latitude.

 

When I polar align on a G11, I get within 5 to 15 arc minutes of true north, you'll probably not do as well.  Whether that is good enough for photography is a big "it depends."  It certainly is good enough for planet imaging.  

 

The main error source on your mount will be periodic error, but polar misalignment will lead to field rotation.  The farther you are from true N, the worse the field rotation problem will be.  

 

On a CG4 I can't imagine you would be well advised to do more than 1 minute exposures and I am having a hard time imagining you'll get a lot of field rotation as a result of that.  If you can use a computerized polar alignment routine to get set up, so much the better, but I'm not sure it will be decisive for your imaging outcomes.

 

One trick is to level the mount as accurately as you can before polar aligning.  Leveling is not at all required for good tracking.  However, if you are carefully leveled when you find Polaris then, when you set up again, if you again carefully level, you will have only one (left to right, or azimuth) dimensions to hunt for Polaris in.  The altitude will already be correctly set.  It is a time saver.

 

Greg N


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#16 sg6

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Posted 21 February 2019 - 03:40 AM

The Latitude scale will only be approximate, hopefully within 5 degrees and maybe 2 or 3. Then comes how level is the mount. A setting on an accurate Latitude scale is only 22 degrees if the mount is 0. In effect the Latitude scale is related to the angle of the mount. So if the mount is level to say +/-2 and the latitude is say +/-3 then you can be up to +/-5 degrees out, or any other other combination between.

 

The Polar scope is tied to the reticle in it by the focal length of the front element.The polar scope should have a low magnification for a wide field.

 

If you have set it all up = Level, Latitude and "Az" then one of the "settings" is wrong. Where and what the wrong one is becomes the question.

 

I don't think the polar scope slides in and out easily, otherwise I would have said slide it out, locate Polaris throught the big hole, center it as best as feasible, then replace the polar scope. However I guess yours is like mine and means dismantling half the mount.




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