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What method do you Polar Align with?

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#1 mpgxsvcd

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Posted 08 April 2013 - 10:27 AM

I know that there are several different ways to polar align like using a Polar Scope, Using an all-star Align function, or simply using the sun or Polaris to guesstimate it. However, I have really begun to like the Polar Finder Scope method.

I went out on Friday night with the intent of seeing how long I could track without guiding. Typically all I do to polar align is line up the Big Dipper in the Polar scope with its orientation in the sky. This time I decided to do it more precisely.

I looked directly at Polaris and noted two stars that were either directly vertical or directly horizontal of each other in the big dipper. Then I rotated the mount and Polar Finder until those stars were either vertical or horizontal in the Polar finder.

It just seems like it is much easier to align based on points that are directly vertical or directly horizontal in relation to each other.

After I accurately placed Polaris in the small circle in the Polar Finder I rotated the scope to verify that my Polar finder was centered in my mount. It was dead on.

Then I started taking some images. I tried 2 minutes and it looked great so I went for 3 minutes and it still looked fine. Then I went for 5 minutes and it definitely started to show some star trails but honestly it was not as bad as I thought it would be.

I never attempted the All-star align simply because Polaris tracked exactly around the small Polar Finder scope all night long. The all-star alignment wouldn’t have helped because I had done the Polar Finder setup so precisely.

This is not to say that the All-star alignment shouldn’t be used. It does a great job especially when you do a true “rough” alignment with the Polar Finder. However, I have noticed that if you do an extremely precise alignment with the Polar Scope then the error tolerance in the All-star alignment is usually greater than it is with an extremely accurate Polar Scope Alignment.

Please note that this is the second Polar Scope that I have owned. I accidentally let the little piece of glass slip in the first one when I was trying to center it. Once it rotates at all you can no longer do a precise alignment in this manner and the All-star alignment will definitely be a better option.

3 minutes for an 800mm scope and a 2x crop factor camera. This is a 1:1 crop from the center of the image. ISO 800.

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#2 mpgxsvcd

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Posted 08 April 2013 - 10:29 AM

Here is the 5 minute image

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#3 mpgxsvcd

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Posted 08 April 2013 - 10:32 AM

Here is 3 minutes.

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#4 mpgxsvcd

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Posted 08 April 2013 - 10:33 AM

And 2 minutes

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#5 mpgxsvcd

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Posted 08 April 2013 - 10:35 AM

And here was 60 Seconds.

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#6 mpgxsvcd

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Posted 08 April 2013 - 10:37 AM

I also found that using the loss-less crop mode for live view was perfect for getting the focus right.

This is a rough focus using the regular live view.

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#7 mpgxsvcd

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Posted 08 April 2013 - 10:38 AM

And this was using the 10x crop mode.

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#8 Jeff2011

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Posted 08 April 2013 - 11:02 AM

Travis,

Interesting results. I have seen other CN members mention that the polar finder scopes did not meet their expectations. I don't have a polar finder scope but I am going to try the following once the clouds clear.

Since Polaris is about 0.7 degrees from the NCP, I am going to see what it looks like in Sky Safari with the view flipped accordingly for my refractor. Then with an eyepiece that has a field of view only slightly larger, I am going to then try to put Polaris at the approximate position in the eyepiece that Sky Safari shows it should be. When I was looking at it last night in Sky Safari that would have been the 5 o'clock position.

I have currently only used the polar align feature of the mount hand control and have been able to get a 2 minute shot without trailing, but that is with a 430mm focal length refractor.

#9 John Carruthers

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Posted 08 April 2013 - 11:24 AM

Having the reticle rotate doesn't prevent accurate polar alignment. So long as it is concentric with the RA axis it's orientation doesn't matter. The hour circle 'can' be made to match your local sidereal time but I've never bothered.
I often have to replace and update reticles to keep them current. It's not uncommon to have to simply replace one that's dropped out (an O ring behind them prevents this happening)
The little circle may be good if it's fairly new but after a few years the NCP drifts in relation to Polaris.

YEAR RA NPD degrees
1990 2h 21m 47' +2.1
2000 2h 32m 44' +1.3
2010 2h 44m 41' +0.5
2020 2h 56m 39' -0.3

http://www.awrtech.c....htm#POLARSCOPE

#10 mpgxsvcd

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Posted 08 April 2013 - 11:48 AM

The important thing to note here is that I am aligning based on the orientation of the big dipper and not its position. That is a critical distinction.

Aligning by position means that you line up Ursa major by the angle it is at in the reticle. Your eyes are not very accurate when trying to estimate an arbitrary angle. However, if you align by the orientation of Ursa Major you can accurately align by using two vertical or horizontal stars.

My observation is that the Polar Finders seem to be accurately aligned from the factory. If you accidently let the glass slip it is very hard to get it back aligned as accurately as the factory. And yes they become less and less accurate over time. However, I bought the one I am using now over 6 months ago and I am still very happy with the results.

I don’t want anyone to get the impression that I am saying that using the Polar Finder is the best way to do it. All I am saying is that precisely aligning by orientation with the Polar Finder is much more accurate than aligning by position or by doing a rough estimate(Placing Polaris in the center of the reticle).

If you can’t do the all-star align for any reason then a precise orientation align is a good option. In addition I don’t believe that you should do a precise orientation align along with an all-star align. The all-star align has error tolerances that in my experience have always been greater than when I do the Precise Polar scope alignment.

I have never been able to get the All-star alignment to improve on my visual Polar Alignment. However, I can get the All-Star alignment to equal my visual alignment by doing a rough estimate first instead of taking the time to do the precise alignment.

YMMV though. Does anyone else use the Polar Finder only?

#11 mpgxsvcd

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Posted 08 April 2013 - 11:51 AM

Since Polaris is about 0.7 degrees from the NCP, I am going to see what it looks like in Sky Safari with the view flipped accordingly for my refractor. Then with an eyepiece that has a field of view only slightly larger, I am going to then try to put Polaris at the approximate position in the eyepiece that Sky Safari shows it should be. When I was looking at it last night in Sky Safari that would have been the 5 o'clock position.


The big issue is that you are putting the scope position and orientation into the mix. If your scope is not exactly in its "home" position your results will be off. Using the Polar finder takes the scope out of the equation completely and just aligns the mount.

#12 psu_13

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Posted 08 April 2013 - 01:34 PM

I've started to use the new polar finder that Astrophysics came up with. It has a reticle that is more like the Tak finders. It's only disadvantage is that it requires the user to carefully align it to the RA axis with some tedious to use push/pull screws. I got it pretty close, but I'm not sure that it held.

Anyway, what I do now it put Polaris close to the right place on the reticle and then use PEMPro's drift align to do the rest. The scope seems to get me within about 5-10 arc minutes, and the final tuning with PEMPro gets it a bit better. If I could remember which knobs make the mount go which direction I'd be able to do this in about 10 minutes, but I always get mixed up. :-)

Pete

#13 andysea

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Posted 08 April 2013 - 03:40 PM

My with NJP I use the built in polar scope.
WIth the AP mount I have been using the Losmandy polarscope but I will be starting to use the right angle polar scope as soon as I receive it. I know two AP owners who just installed it with no tweaking at all and it seems to be working great.

#14 orion69

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Posted 08 April 2013 - 03:58 PM

In addition I don’t believe that you should do a precise orientation align along with an all-star align. The all-star align has error tolerances that in my experience have always been greater than when I do the Precise Polar scope alignment.

I have never been able to get the All-star alignment to improve on my visual Polar Alignment. However, I can get the All-Star alignment to equal my visual alignment by doing a rough estimate first instead of taking the time to do the precise alignment.


I presume you are talking about ASPA? In that case you must be doing something wrong because you should get much better polar alignment with ASPA compared to polar scope. That may not be noticable in short subs but over 15min it becomes very noticable.

#15 hottr6

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Posted 08 April 2013 - 05:06 PM

When I look at your images, why do I see pairs of identically illuminated "stars", all with the same separation. Dead pixels?

#16 Dwight J

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Posted 08 April 2013 - 06:23 PM

Hi Travis: try using your camera to assist you in getting a better polar alignment once you have used your polar scope. It is a modified drift alignment which is best explained by this link: http://www.observato...ent_CCDv1-1.pdf
A camera such as yours is just as capable to do this method.

#17 Phil Sherman

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Posted 08 April 2013 - 09:24 PM

I've carefully aligned and marked my mount so I can set it with the polar reticle crosshairs vertical and horizontal when the mount is attached to a level tripod. When Power is applied to the handset, it gives me a "clock position" for Polaris on a 12 hour clock. doubling the difference between this value and 12:00 gives me a 24 hour displacement of the mount. I use the setting circles to move the mount the appropriate amount then polar align in the little circle.

I'm usually only a few minutes off on polar alignment. Accuracy can be improved by verifying that the azimuth adjustment of the mount is parallel to one of the crosshair lines before rotating the mount to Polaris' current position.

This is a manual version of the polar alignment routine used by EQMOD. EQMOD also turns on tracking, which keeps the targeting circle correctly positioned as you adjust the mount.

If I'm setting up for a week of imaging, I'll then do a photographic drift alignment.

Phil

#18 David Pavlich

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Posted 08 April 2013 - 09:32 PM

I don't have a polar scope. I use Pempro's polar alignment routine.

David

#19 gezak22

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Posted 08 April 2013 - 10:00 PM

I have a GM8, and I use the polar scope to align it roughly. I then fine tune it using the drift method with PHD. For me this is the best compromise between speed and accuracy.

#20 tboconnor

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Posted 08 April 2013 - 10:13 PM

I'm in the southern hemisphere - I've never been tempted to use my polar scope :)

I use Celestrons All star, and it works really well so far.

#21 pjensen

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Posted 08 April 2013 - 10:17 PM

I know that there are several different ways to polar align like using a Polar Scope, Using an all-star Align function, or simply using the sun or Polaris to guesstimate it. However, I have really begun to like the Polar Finder Scope method.


Bought a polar alignment scope 2 weeks ago for my CG5. Used it several times now and it works great. In a minute the tripod is dead on (move the tripod, raise/lower a tripod leg).

From then on (after the 2+4 star alignment), the go to's are the best they have ever been.

For the first time, I am getting good goto performance out of this scope. I been seeing new Messier objects on every session.

#22 mpgxsvcd

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Posted 08 April 2013 - 11:15 PM


In addition I don’t believe that you should do a precise orientation align along with an all-star align. The all-star align has error tolerances that in my experience have always been greater than when I do the Precise Polar scope alignment.

I have never been able to get the All-star alignment to improve on my visual Polar Alignment. However, I can get the All-Star alignment to equal my visual alignment by doing a rough estimate first instead of taking the time to do the precise alignment.


I presume you are talking about ASPA? In that case you must be doing something wrong because you should get much better polar alignment with ASPA compared to polar scope. That may not be noticeable in short subs but over 15min it becomes very noticable.


Show me any unguided 15 minute sub with an 800mm or more scope that doesn't have significant star trails. I don't believe you can do a perfect 15 minute sub unguided with ANY of the Polar Alignment methods. Even with perfect Polar Alignment you will still get star trails after 5 minutes unguided.

#23 mpgxsvcd

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Posted 08 April 2013 - 11:17 PM

I'm in the southern hemisphere - I've never been tempted to use my polar scope :)

I use Celestrons All star, and it works really well so far.


Yes the Polar Scope really doesn't help much down south.

#24 orion69

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Posted 09 April 2013 - 01:16 AM


In addition I don’t believe that you should do a precise orientation align along with an all-star align. The all-star align has error tolerances that in my experience have always been greater than when I do the Precise Polar scope alignment.

I have never been able to get the All-star alignment to improve on my visual Polar Alignment. However, I can get the All-Star alignment to equal my visual alignment by doing a rough estimate first instead of taking the time to do the precise alignment.


I presume you are talking about ASPA? In that case you must be doing something wrong because you should get much better polar alignment with ASPA compared to polar scope. That may not be noticeable in short subs but over 15min it becomes very noticable.


Show me any unguided 15 minute sub with an 800mm or more scope that doesn't have significant star trails. I don't believe you can do a perfect 15 minute sub unguided with ANY of the Polar Alignment methods. Even with perfect Polar Alignment you will still get star trails after 5 minutes unguided.


Why would I do 15min unguided subs???

You can shoot long unguided subs only with high end mounts but they certainly do not use polar scope for PA except for rough PA to get them faster start.

#25 mpgxsvcd

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Posted 09 April 2013 - 10:24 AM

Why would I do 15min unguided subs???

You can shoot long unguided subs only with high end mounts but they certainly do not use polar scope for PA except for rough PA to get them faster start.


You should have written "I can shoot long unguided subs only with high end mounts but I certainly do not use polar scope for PA except for rough PA to get me a faster start." I can and do get longer subs simply by aligning with the Polar Finder. I only use the All-star Align and drift align when there is something preventing me from using my Polar Scope.

I think part of the problem is that some people have not figured out how to do a precise Polar scope alignment so they just assume it can't be done. Once a few people say that it isn't accurate then it gets the stereo-type of being inaccurate. You have to be extremely precise when doing a Polar Scope alignment for it to work. You also have to be willing to bend down and look through it. In addition you have to be able to shine a light in the front of it and hold your head straight up and down to line it up properly.

All of those things typically make people shy away from doing it that precisely and those are legitimate reasons.

However, that doesn't mean that the Polar Scope cannot be used for a precise Polar alignment without ever doing the All-star align or even a drift align. It can be done. All I am doing is trying to show everyone the procedures for doing it precisely and accurately with the Polar Scope.

A precise All-star align is not always possible if there are no stars in the right place, your alignment is way off, or you don't have a precise way of doing the all-star alignment. In those cases you might choose to just do a precise Polar Scope alignment. That is not to say that it is better. Instead it is just another way of doing it.

I always like to have options in case something goes wrong.

However, I also say that you should pick one method and stick to it for each session. If you are going to all-star align then don't try to do a precise Polar Scope Alignment. The point of doing a precise Polar Scope alignment is that you won't have to do an all-star alignment afterwards. If you get the Polar Scope alignment done correctly all the all-star alignment will do is mess up what you have already done correctly.

If it isn't broken don't fix it.






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