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Telescope alignment: do I have this right?

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#1 lexbrook

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Posted 21 October 2019 - 08:30 PM

I have an IEQ45-Pro mount but I think my question applies to just about any EQ mount. To align my scope I do the following:

1) Level the tripod with a bubble level (I think this just makes it easier to find Polaris later)

2) Use my built in Polar scope and move the tripod left/right and the az adjustment up/ down to find polaris in the polar scope( this gets polaris aligned to perhaps a degree or two).

3) Look at the position of polaris in my handbox to see where it should be with respect to true north. Use fine adjusting screws to adjust alt and az to match the actual position of polaris to the intended position of polaris probably accurate to a few minutes or so.

 

confusion starts here......

 

4) I then align the pointing of my finder scope to where I think true north is based on the rotation of polaris. I don't have a perfect illuminated reticle to do this, but I get it as close as possible.

5) Then I set the zero position of the scope

6) The I perform a 3 star alignment (almost always with ease)

 

My problem is when doing AP my tracking is often variable from night to night. Sometimes I'm OK 30 seconds unguided and sometimes just 10 seconds. Am I doing something wrong? Missing a step?

 

Any help would be appreciated.

Regards,

Dave Holbrook

 

 



#2 mich_al

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Posted 21 October 2019 - 09:47 PM

Dave

  Search out the 'alignment tips' thread on this site to save yourself much wasted time and troubles.



#3 kathyastro

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Posted 22 October 2019 - 11:38 AM

3) Look at the position of polaris in my handbox to see where it should be with respect to true north.


4) I then align the pointing of my finder scope to where I think true north is based on the rotation of polaris. I don't have a perfect illuminated reticle to do this, but I get it as close as possible.

First, have you calibrated your polar scope?  This involves making sure that the central cross-hairs of the polar scope exactly match the RA axis.

 

"The position of Polaris with respect to true north"... How are you doing that?  There are a couple of common techniques: the clock face method or the hour angle method.  The clock face method is the simplest, provided your hand controller gives you the clock position.  Other methods require that you remain aware of your orientation.  The polar scope is, of course, a refractor, and the image is inverted.  So, while looking through it, the horizon is up, the zenith is down, east is left, and west is right.  And Polaris rotates counterclockwise around the pole.

 

If you get it wrong, you may not notice right away, since Polaris is in the polar scope, so you can't be too far off the pole.  You will just find poor tracking after a while.

 

I am not sure what you are trying to accomplish with aligning your finder.  If you are just aligning it with the imaging scope, aim the imaging scope at Polaris, centre it, then adjust the finder until Polaris is in the cross-hairs.

 

Setting an accurate zero position can be done with a level.  Or if you already have Polaris in the scope, you can set the zero position there, though it will be out by 45 arc-minutes.  The zero position will affect the accuracy of your gotos, primarily the centering of your three alignment stars.  It won't affect tracking.



#4 Blackbelt76

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Posted 22 October 2019 - 12:54 PM

I have an IEQ45-Pro mount but I think my question applies to just about any EQ mount. To align my scope I do the following:

1) Level the tripod with a bubble level (I think this just makes it easier to find Polaris later)

2) Use my built in Polar scope and move the tripod left/right and the az adjustment up/ down to find polaris in the polar scope( this gets polaris aligned to perhaps a degree or two).

3) Look at the position of polaris in my handbox to see where it should be with respect to true north. Use fine adjusting screws to adjust alt and az to match the actual position of polaris to the intended position of polaris probably accurate to a few minutes or so.

 

confusion starts here......

 

4) I then align the pointing of my finder scope to where I think true north is based on the rotation of polaris. I don't have a perfect illuminated reticle to do this, but I get it as close as possible.

5) Then I set the zero position of the scope

6) The I perform a 3 star alignment (almost always with ease)

 

My problem is when doing AP my tracking is often variable from night to night. Sometimes I'm OK 30 seconds unguided and sometimes just 10 seconds. Am I doing something wrong? Missing a step?

 

 

My question would perhaps not go so much to your alignment procedure as it seems to be consistent.

 

What are you photographing? Same time every night when you set up?

How many times have you photographed it? (i.e) Is it the same object?

What do you mean by "my tracking is often variable..."? Star trails in RA or Dec or both?

I assume you set up each night (i.e) Not a permanent pier.Is your base plate to tripod secure? Any play?

 

From 30 secs to 10 secs, depending on your camera settings, that is not that much deviation. Possible atmospheric thermal problem?

 

Personally, I would track a object for 5 minutes, preferably a star to see if the guiding error is constant or variable.

 

Locating tracking errors is like the golf swing; we diagnose one thing at a time, not motor & polar alignment.

 

Look for reproducible errors.

 

 

 


Edited by Blackbelt76, 22 October 2019 - 12:56 PM.



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