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Need help polar aligning my EXOS2-GT mount

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#1 jstrandberg

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Posted 21 March 2019 - 10:41 AM

I have a couple of questions relating to achieving precise (well precise enough for 60-90 second exposures with my AT72) polar alignment with my EXOS-2GT mount.  I have been doing astrophotography with my Canon T2i for about a year just fine (mostly with my 85mm and 135mm lenses).  Just recently I bought a 200mm lens and also started using an AT72. But, my alignment skills don't seem to be up to the job with the longer lenses with exposures past 30 seconds. After checking my polar scope alignment with my mount and making some small adjustments, I was still getting small star trails at my test exposures of  60 seconds of maybe 4 or 5 star diameters.

 

Unfortunately, unlike the Celestron Nexstar +, the EXOS hand controller has no polar alignment function so I am limited to using the polar scope for alignment.  So, I have a couple questions that I hope you forum members can help me with.

 

My EXOS-2GT reticule looks exactly like the one at the bottom of this post which I found in a Vixen manual.

 

First question: As you can see, the reticule pattern on the EXOS polar scope is ancient.  With Polaris being at about 89d21m I first tried placing it at the intersection of the 40' mark.  This shortened the trail a little, but they were still about 3 star diameters in 60 second exposures.  Even though this picture is from a Vixen manual, a couple days ago I decided to try and estimate what the offset illustrated would be for 2019 and applied it for some 60 second test images. I have seen a slight improvement, down to maybe 2 star diameters, after applying the offset, so I am unsure if I should apply the offset or not, or try to tweek the positioning to find the exact right position. Any thoughts?

 

Second question: The other problem with using this reticule is that there is no precise way to align the reticle pattern with the position of Polaris as shown in PolarFinder or PolarScope, so I am wondering if I might be able to use a different polar scope with the mount that may have a "better" reticule pattern, say like the Takashai pattern, that would allow for more precise alignment.

 

Thanks in advance for any help.

Attached Thumbnails

  • Vixen PAS Reticle N.jpg

Edited by jstrandberg, 21 March 2019 - 10:42 AM.


#2 ecuador

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Posted 21 March 2019 - 01:29 PM

If you have an iOS device, Polar Scope Align has a method for polar aligning with your polar scope that gives very accurate results (choose the correct reticle and read the in-app instructions). The free version is enough.



#3 jstrandberg

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Posted 21 March 2019 - 02:42 PM

If you have an iOS device, Polar Scope Align has a method for polar aligning with your polar scope that gives very accurate results (choose the correct reticle and read the in-app instructions). The free version is enough.

Yes, that would be nice.  No smartphone and no laptop.



#4 dakinemaui

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Posted 21 March 2019 - 03:15 PM

Live view and drift alignment.



#5 ImNewHere

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Posted 21 March 2019 - 05:46 PM

Look up kochab clocking for Meade LXD75 and do the same thing with yours. That will give a very good PA. It is basically the same mount and same polar scope.

Actually here you go: http://www.thestarde...Polaralign.html



#6 OldManSky

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Posted 21 March 2019 - 06:26 PM

"...so I am limited to using the polar scope for alignment."

 

No, you're not :)

 

You have a DSLR, you said...try this:

 

http://observatory.d...ent_CCDv1-1.pdf

 

In 10 minutes you can be well-aligned and imaging!


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#7 Messierthanwhat

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Posted 21 March 2019 - 10:24 PM

Yes, that would be nice.  No smartphone and no laptop.

And no excuse. You can buy a second-hand smartphone these days for peanuts. The one I'm using cost $4 at a thrift shop, and there are hundreds available on ebay for less than $20. They work fine for this purpose without any requirement that you contract for phone service. Just connect to the proper store via wi-fi and install and use the free app.



#8 jstrandberg

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Posted 21 March 2019 - 10:53 PM

"...so I am limited to using the polar scope for alignment."

 

No, you're not smile.gif

 

You have a DSLR, you said...try this:

 

http://observatory.d...ent_CCDv1-1.pdf

 

In 10 minutes you can be well-aligned and imaging!

OK, this looks promising.  My only question is, do I have to move exactly south from Polaris to 0-degrees after I do my initial Polar alignment or will any more or less southerly star a 0-degrees work?



#9 jstrandberg

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Posted 21 March 2019 - 11:34 PM

And no excuse. You can buy a second-hand smartphone these days for peanuts. The one I'm using cost $4 at a thrift shop, and there are hundreds available on ebay for less than $20. They work fine for this purpose without any requirement that you contract for phone service. Just connect to the proper store via wi-fi and install and use the free app.

I did not know that.  I went to the Polar Scope Align page and it does look like it would do the trick, but I thought you would need a cell provider.  Guess I will look for an old iPhone then so I can try this app.



#10 Phil Sherman

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Posted 22 March 2019 - 07:41 AM

OK, this looks promising.  My only question is, do I have to move exactly south from Polaris to 0-degrees after I do my initial Polar alignment or will any more or less southerly star a 0-degrees work?

I use this technique frequently. There's an error in the pdf instructions though. Start the image, slew E, then slew W. With your slew rate set to 1x sidereal, the E slew just stops the mount's tracking while the W slew catches it up. I do this with a 70 second exposure with the E slew 30 seconds and the W slew 35 seconds. This makes the return trail pass through the star made by the 5 second tracked portion of the exposure. I found it easier to judge the alignment this way.

 

Azimuth adjustments are made using measurements on the celestial equator near the meridian. Altitude is done on the celestial equator 25-30 degrees above the E or W horizon. There's no need to locate a specific star because there will always be stars visible in the image.

 

Make sure your tripod is leveled before attaching the mount. If it's not level, the two adjustments interact with each other.


Edited by Phil Sherman, 22 March 2019 - 07:44 AM.

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