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Cem120 star pointing-alignment issues? Polar iterate mode, error messages when doing 2 star?

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#1 markm75c

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Posted 23 September 2019 - 11:23 AM

I have my cem120 now permanently outside, as the nexdome is weeks away.  I've been trying to work through alignment issues.

 

So far i managed to use sharpcap to polar align to about 0'14-0'24" or so according to its info, via the 60mm guidescope + asi290mm mini.

 

Despite this, star pointing accuracy has been suspect.

 

I tried polar iterate alignment too to be safe (though i didnt touch azi or alt knobs this time after sharpcap, just left/right arrow is all i had to do).  When i did vega and deneb, surprisingly they were close in view.  It said to bring the star to about 1/2" from center which i assumed means for instance, off to the left side a tad from center.  I'm not sure if this is how it supposed to work, but each time i'd hit enter it would move to the other star and keep cycling back and forth, no message about "completed".

 

Then i decided to do 2 star align (also tried 1 and 3, same result), i would line up the first star, which in this mode was often off by a bit using my red dot as the guide, bring to center hit enter, then when you would reach the last alignment star and hit enter i get.. "Please run any alignment procedure first!"

 

I'm confused at this point, with sharpcap polar alignment looks good, even polar iterate from the HC was close.  If i do view model error on the HC it gives the same error.

 

What am i missing here?

Thanks in advance



#2 DuncanM

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Posted 23 September 2019 - 12:00 PM

I have my cem120 now permanently outside, as the nexdome is weeks away.  I've been trying to work through alignment issues.

 

So far i managed to use sharpcap to polar align to about 0'14-0'24" or so according to its info, via the 60mm guidescope + asi290mm mini.

 

Despite this, star pointing accuracy has been suspect.

 

I tried polar iterate alignment too to be safe (though i didnt touch azi or alt knobs this time after sharpcap, just left/right arrow is all i had to do).  When i did vega and deneb, surprisingly they were close in view.  It said to bring the star to about 1/2" from center which i assumed means for instance, off to the left side a tad from center.  I'm not sure if this is how it supposed to work, but each time i'd hit enter it would move to the other star and keep cycling back and forth, no message about "completed".

 

Then i decided to do 2 star align (also tried 1 and 3, same result), i would line up the first star, which in this mode was often off by a bit using my red dot as the guide, bring to center hit enter, then when you would reach the last alignment star and hit enter i get.. "Please run any alignment procedure first!"

 

I'm confused at this point, with sharpcap polar alignment looks good, even polar iterate from the HC was close.  If i do view model error on the HC it gives the same error.

 

What am i missing here?

Thanks in advance

Polar Iterate alignment (PIA) is only used for mounts that have not been previously polar aligned by another method. Sharpcap is inherently far more accurate then Polar Iterate Alignment. If you have previously physically PAed using Sharcap then do not use PIA - it is pointless at best, and at worst will destroy any really accurate PA, if you physically adjust the mount based upon PIA recommendations.

 

Instead, use the 3 star alignment procedure:

5.3.4. Three Star Alignment
The three-star alignment will further determine the cone error between the OTA and mount axis.
The system will use these data to calculate the goto model. If the cone error is big enough, it is
suggested to shim the OTA in DEC to minimize it.
Press MENU => “Alignment” => “Three Star Alignment.” A list of alignment stars that are
above the horizon is computed based on your local time and location. With the mount at the Zero
Position, use the▲ and ▼ buttons to select the first alignment star and press ENTER. Center the target
in your eyepiece using the arrow keys. Press ENTER when finished. The hand controller will prompt
you to choose a second star. Select third star after the mount aligned to the second star.
The system will display the pointing and cone errors after the three star alignment accepted.
The system will update the pointing model accordingly.

http://www.ioptron.c...Instruction.pdf

 

When you use the 3 star alignment you centre the target star using the buttons on the hand controller. Do not adjust the alt/az knobs on the mount.

 

The most accurate method of accurately pointing the mount to your desired target, is to use plate solving.



#3 markm75c

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Posted 23 September 2019 - 12:14 PM

Polar Iterate alignment (PIA) is only used for mounts that have not been previously polar aligned by another method. Sharpcap is inherently far more accurate then Polar Iterate Alignment. If you have previously physically PAed using Sharcap then do not use PIA - it is pointless at best, and at worst will destroy any really accurate PA, if you physically adjust the mount based upon PIA recommendations.

 

Instead, use the 3 star alignment procedure:

When you use the 3 star alignment you centre the target star using the buttons on the hand controller. Do not adjust the alt/az knobs on the mount.

 

The most accurate method of accurately pointing the mount to your desired target, is to use plate solving.

Ok, yeah thats what i tried to do, was any of the star alignment options, the 3 star included.

 

But every time i'd finish the last star the HC gave me the error "Please run any alignment procedure first"

 

I'm not sure why or what that means?

 

 

I've yet to learn/use plate solving too, i'd like to, i have nina installed, was hoping to learn it, though i have a few tutorials bookmarked on plate solving using apt too.



#4 DuncanM

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Posted 23 September 2019 - 01:45 PM

Ok, yeah thats what i tried to do, was any of the star alignment options, the 3 star included.

 

But every time i'd finish the last star the HC gave me the error "Please run any alignment procedure first"

 

I'm not sure why or what that means?

 

 

I've yet to learn/use plate solving too, i'd like to, i have nina installed, was hoping to learn it, though i have a few tutorials bookmarked on plate solving using apt too.

Is "the red dot" a zero power finder? If so it might not be accurate enough.

 

It's probably best to use Sharpcap and centre the alignment star via an on-screen cross hair or use a cross hair EP. Accurate alignment of the target stars is needed to allow the alignment routine to work. However, it's possible that firmware updates have modified the 3-star alignment, and honestly I've always just used plate solving, which in Astroart 7 is dead simple. I don't use Nina so I can't help with that.



#5 markm75c

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Posted 23 September 2019 - 03:13 PM

Is "the red dot" a zero power finder? If so it might not be accurate enough.

 

It's probably best to use Sharpcap and centre the alignment star via an on-screen cross hair or use a cross hair EP. Accurate alignment of the target stars is needed to allow the alignment routine to work. However, it's possible that firmware updates have modified the 3-star alignment, and honestly I've always just used plate solving, which in Astroart 7 is dead simple. I don't use Nina so I can't help with that.

Unsure what zero power means (no zoom) but, i'm not basing it strictly on the red dot, actually have the red dot and a celestron 9x50 on there, so first i get the star centered in the eyepiece (i do have a cross hair eyepiece but havent used yet), using 25mm 1.25" eyepiece, then line up the red dot and 9x50, then try the 3 star align and then it fails

 

I'm wondering if it could be related to the firmware update i did, i had the hc connected but it wouldnt update, gave an error, i forgot about this and havent tried since.

Perhaps i should try to rerun the update i guess.



#6 markm75c

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Posted 24 September 2019 - 11:28 AM

Update: so i did get things working.

 

I had to manually do the rs232 cable from the hc, i think it updated, at least it seemed to say it did (though when i view the file name and the version on it, doesnt seem quite the same).

 

I then made sure to use the eyepiece with cross hair.  Not sure which did it, but 3 star autoalign got things pretty close, slightly off center (not sure how to tell in arcsec or degrees off, but its slightly off).

 

I'm still having an issue with imaging more than 60 seconds unguided (or guiding with phd2 not quite working), 120sec images develop blurs, but not every time (sharpcap)

 

The other thing i'm still unclear on, is why/when ever to use the "Home" feature on the HC.  I always return it to "zero" position, aiming north, ota on top, unsure what home does differently.


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