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plate solve to find alignment issues

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#1 Rmorgan

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Posted 13 September 2019 - 08:50 PM

Is it possible to take a few plate solves and calculate drift or alignment issues?  Somewhere I saw a method where a plate solve was taken and then the mount was moved in Ra a certain distance and another plate solve was taken.  This wasn't near the poles but closer to the equator.   The error in dec or ra could be determined so then the mount could be adjusted.  any ideas?

 

--Rob



#2 Rovert9988

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Posted 13 September 2019 - 09:15 PM

You can use Sharpcap to take images and plate solve for the polar alignment. Many people report being happy with it, though I've never used it.

 

I do use Stellarium and PlateSolve 2 for alignment with plate solving though. Basically do a go-to, plate solve, then update the pointing model with that new info. It takes a couple minutes each time, and after 2 or 3 solves it's generally pretty spot on.



#3 Brett Waller

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Posted 13 September 2019 - 09:38 PM

It's nothing more than solving several simultaneous equations in spherical trigonometry, which the computer could do very quickly, but by the time you collected the data, there are about a dozen other ways to achieve polar alignment that are easier and faster. And since most mounts don't have calibrated scales to precisely adjust the azimuth and altitude to arc minute precision, you will get into several iterations just to get close.  So doable, but not really practicable.

 

Perhaps the next generation of Go-To mounts will incorporate motorized adjustments using encoders, but I suspect that would add substantially to the overall cost.

 

Brett



#4 rgsalinger

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Posted 13 September 2019 - 09:52 PM

There used to be a program called "alignmaster" that did exactly that. You might want to see if it's around. I have not seen it for years.

Rgrds-Ross


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#5 Rmorgan

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Posted 13 September 2019 - 10:00 PM

It's nothing more than solving several simultaneous equations in spherical trigonometry, which the computer could do very quickly, but by the time you collected the data, there are about a dozen other ways to achieve polar alignment that are easier and faster. And since most mounts don't have calibrated scales to precisely adjust the azimuth and altitude to arc minute precision, you will get into several iterations just to get close.  So doable, but not really practicable.

 

Perhaps the next generation of Go-To mounts will incorporate motorized adjustments using encoders, but I suspect that would add substantially to the overall cost.

 

Brett

I would be interested in any spherical trigonometry if anyone knows more about it.  I would assume polar alignment was already completed but not accurate and looking at this to possible calculate differences. Possible alternative to drift alignment.  Collecting the data or manipulating the mount isn't a problem.

 

--Rob



#6 bobzeq25

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Posted 14 September 2019 - 12:53 AM

I would be interested in any spherical trigonometry if anyone knows more about it.  I would assume polar alignment was already completed but not accurate and looking at this to possible calculate differences. Possible alternative to drift alignment.  Collecting the data or manipulating the mount isn't a problem.

 

--Rob

The real alternative to drift is either a PoleMaster or Sharcap Pro.  They use platesolving (behind the scenes) to polar align very fast, easy and accurately.  Just one of the many things a computer can do better than you can.  <smile>

 

I've never been able to do a drift alignment any better than the PoleMaster.  In any event, it's "good enough" to avoid any issues imaging.

 

After you use any method, you can easily check the accuracy by running guiding assistant in PhD2.


Edited by bobzeq25, 14 September 2019 - 12:54 AM.


#7 AhBok

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Posted 14 September 2019 - 01:06 PM

Is it possible to take a few plate solves and calculate drift or alignment issues?  Somewhere I saw a method where a plate solve was taken and then the mount was moved in Ra a certain distance and another plate solve was taken.  This wasn't near the poles but closer to the equator.   The error in dec or ra could be determined so then the mount could be adjusted.  any ideas?

 

--Rob

You could platesolve and note the RA and DEC coordinates. The let you scope track for 30min, take an exposure and platesolve again. Then you could note the error in RA and DEC. If you time this properly, it would be trivial to compute drift for each axis in arcsec/sec. 


Edited by AhBok, 14 September 2019 - 01:07 PM.



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