Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

CPC alignment procedure?

  • Please log in to reply
4 replies to this topic

#1 Gary.McK

Gary.McK

    Messenger

  • -----
  • topic starter
  • Posts: 437
  • Joined: 29 Jan 2009
  • Loc: Geelong, Australia

Posted 26 January 2020 - 08:34 PM

OK, I'm prepared to admit I'm as thick as two planks, but I can't find a detailed outline of the procedure for final movements for alignment in my case.

 

I actually bought The Nexstar User Guide from Amazon, but found it not quite fully explaining things for my use case.

 

I'm in the Southern Hemisphere.

I use a Starsense

 

The Starsense hand control is set at Positive and Positive for Alt/Az

 

Apparently the altitude movement is fixed at positive in the Starsense hand controller

The Azimuth movement should be changed to negative (both of these came from Mike Swanson's great book.)

 

Which keys should I use for final centring / calibration of the Starsense? I had been using up and right as per the CPC manual with the default Alt/Az settings, but find I'm getting a significant drift when tracking (more than just backlash takeup). Should I switch to Up and Left after changing the Starsense Alt/Az settings t Positive and Negative for Alt/Az?

 

Help gratefully received!

 

Gary


Edited by Gary.McK, 26 January 2020 - 08:50 PM.


#2 Migwan

Migwan

    Surveyor 1

  • *****
  • Posts: 1,685
  • Joined: 24 Jul 2017
  • Loc: Meeechigan

Posted 26 January 2020 - 11:05 PM

Apologies if you have already considered this, but check your level.  My bubble level was way off and I had trouble with drift and loss of alignment after slewing to a few targets.  A torpedo level resolved the issue with mine.  

 

I have found that up and right or down and left don't make any difference with my CPC1100, just as long as the star is still centered after "alignment success" appears.   Of course that could just be true with my scope.  I use the two star alignment.

 

Hope its that simple.

 

jd



#3 Michael_Swanson

Michael_Swanson

    Author of The NexStar Users Guide

  • *****
  • Vendors
  • Posts: 2,564
  • Joined: 23 Apr 2003

Posted 27 January 2020 - 01:03 AM

OK, I'm prepared to admit I'm as thick as two planks, but I can't find a detailed outline of the procedure for final movements for alignment in my case.

 

I actually bought The Nexstar User Guide from Amazon, but found it not quite fully explaining things for my use case.

 

I'm in the Southern Hemisphere.

I use a Starsense

 

The Starsense hand control is set at Positive and Positive for Alt/Az

 

Apparently the altitude movement is fixed at positive in the Starsense hand controller

The Azimuth movement should be changed to negative (both of these came from Mike Swanson's great book.)

 

Which keys should I use for final centring / calibration of the Starsense? I had been using up and right as per the CPC manual with the default Alt/Az settings, but find I'm getting a significant drift when tracking (more than just backlash takeup). Should I switch to Up and Left after changing the Starsense Alt/Az settings t Positive and Negative for Alt/Az?

 

Help gratefully received!

 

Gary

Hi Gary,

 

Thanks for buying the book!

 

First, as you are in the Southern Hemisphere, you would want to the azimuth GoTo Approach to negative.  This would then call for final movements centering the calibration star ending with the DOWN and LEFT arrow buttons. 

 

However, when testing for the book, I found a bug in the GoTo Approach setting in StarSense (page 138).  Even after changing to negative, the scope ignores the setting and continues to use the positive GoTo Approach on both axes.  It is possible Celestron fixed this bug after I pointed it out, but my StarSense now lives a few thousand miles away at my son's house and I can't test to be certain.  The test would be that after changing azimuth GoTo Approach to negative, are the final motions when moving to each alignment position up and left and when you GoTo an object, are the final motions up and left?  

 

If they did fix the GoTo Approach bug, set azimuth GoTo Approach to negative and use final movements with the DOWN and LEFT arrow buttons.  If they did NOT fix the bug, you must in fact use final movements with the DOWN and RIGHT arrow buttons when centering the calibration star.  (The DOWN arrow is assuming you are centering at a slew rate of 6 or lower when the hand control reverses the up/down arrow movements.)

 

And, if they didn't fix the bug, since most objects you are viewing are moving to the left, it is more important you adjust your anti-backlash settings since the GoTo Approach ends moving the wrong direction (to the right) for most objects.

 

That said, the GoTo Approach and final centering motion really only significantly affects GoTo accuracy, not tracking.  If your GoTo accuracy is good and you are 100% certain your tracking drift is not backlash related, something else is going on.

 

When you say the drift is more than you can attribute to backlash, do you mean to say that once you center an object using arrow buttons that take out all backlash (meaning in the direction the object is moving in the sky), it generally stays centered but slowly drifts out of the field of view?  Or is it really moving quickly out of the field of view?  And if you leave it drift, does it eventually settle into tracking the sky accurately (though your object may even have initially drifted)?

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#4 Gary.McK

Gary.McK

    Messenger

  • -----
  • topic starter
  • Posts: 437
  • Joined: 29 Jan 2009
  • Loc: Geelong, Australia

Posted 27 January 2020 - 03:27 AM

Thanks for the reply Mike.  When I said drift out of field, I meant that after centering an object, it will progressively drift across the field and slowly move across the field, and eventually out of the field. It is like the tracking rate is not quite right. I have been using the bubble level in the tripod for levelling, but after reading that this is frequently not correct, I bought a good quality bubble level from a hardware store to cross check the tripod. Haven't yet had a chance to check it. If the bubble level is off, could this be the cause of the problem? For power I am using a 10amp lab power supply.

Cheers

Gary



#5 Michael_Swanson

Michael_Swanson

    Author of The NexStar Users Guide

  • *****
  • Vendors
  • Posts: 2,564
  • Joined: 23 Apr 2003

Posted 28 January 2020 - 06:27 AM

Hi Gary,

 

Leveling the tripod has no effect on alt-az tracking with the exception of One Star and Solar System align (NexStar hand control).  As long as the alignment is successful, the tripod was level enough.

 

So, even after the object drifts out of the field of view, does it ever stabilize (not something you likely tested before so something to check next time).

 

Also, what eyepiece are you typically using in this case?

 

Best regards,
Mike Swanson
https://www.NexStarSite.com




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics