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LX600 - Piggyback Imaging - Starlock issue ? HELP

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#1 kzar

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Posted 14 June 2021 - 02:49 AM

Dear astro friends,

 

I would be very grateful if you could help me in understanding the below issue(s) which I am about to describe.

 

First, after several weeks of efforts in building-up my new roll-off observatory, I finally had yesterday the chance to give a try to my freshly installed equipment by pointing my gear towards NCG 6960. As of now, I have the following rigs (see attached image) :

 

• Main Scope : LX600 14" permanently installed on a pier (with x-wedge) which I plan to use for very faint DSO (galaxies, etc.)
• Small refractor piggyback on the main scope (for wide-field imaging)
• Starlock as the main guiding system

 

Before imaging, I went though the following steps

1. Make sure that I have a "perfectly" balanced equipment (vertically, horizontally, etc.)
2. PEC training of the the mount (Did it a few days ago)
3. Starlock Auto Rate Calibration for a "smooth" tracking (got 33% & 35% rate)
4. Then I deactivated the High Precision Pointing in Starlock to be able to plate solve (successful with APT tool)

 

After step 4, I started imaging NCG 6960 with the small refractor (60 x 240 sec/exposure). Just to make sure that everything was running as planned, I did check the first 6 shots (so far so good).

 

However, when I went through the images this morning, I faced the following issues :

 

  1. Despite having perfectly centered the target by using the goto++ option in APT, the target was drifted away from the center as the night goes on (see below links, three images as examples @ 00.53, 02.06, 3.40 = sorry for the poor quality, had to downsize a lot...).
  2. I noticed also stars trailing on some images.

 

Questions :

 

  1. what would be the reason (s) of having the target being drifted away from the center of the image ?
  2. I had also star trailing on some images. Could that also be related to the image being shifted from the center, or due to Starlock ?

 

Additional thought : as for my setup, would recommend to use an OAG with the small refractor while imaging wide-filed DSO rather than using Starlock (i.e. use only Starlock when imaging with the 14"?)

 

I thank you very much in advance for your kind support.

 

Regards from Switzerland.
Aygen

 

PS EDIT : I have just realized that I probably forgot to take out the cap of the small camera sensor (on Starlock) (I don't recall having taking it out...)shocked.gif  ..... !!!! Do you think it might have caused the above mentioned issues (drift, star trailing, etc.) ?? confused1.gif

Attached Thumbnails

  • 00-53.jpg
  • 02 06 S.jpg
  • 03-40 S4.jpg
  • LX Setup.jpg

Edited by kzar, 14 June 2021 - 05:12 AM.


#2 michael8554

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Posted 14 June 2021 - 06:54 AM

I don't believe your 4 minute images would be so good if Starlock wasn't guiding.

 

Your images appear to be static in RA, but drifting in Dec.

 

I assume your Polar Alignment is better than 5arcmins ?

 

I can't see how rigidly the refractor is mounted, but if it was loose in Dec I would expect a lot of stars trailing in Dec in your images, given the total amount of drift.

 

So I'm afraid I don't have an explanation.

 

Incidentally, all those cables dragging on the ground isn't good for guiding, gather them up in smooth loops attached to the fork arms.

 

And it's NGC, not NCG - just saying   :->


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#3 kzar

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Posted 14 June 2021 - 07:39 AM

I don't believe your 4 minute images would be so good if Starlock wasn't guiding.

 

Your images appear to be static in RA, but drifting in Dec.

 

I assume your Polar Alignment is better than 5arcmins ?

 

I can't see how rigidly the refractor is mounted, but if it was loose in Dec I would expect a lot of stars trailing in Dec in your images, given the total amount of drift.

 

So I'm afraid I don't have an explanation.

 

Incidentally, all those cables dragging on the ground isn't good for guiding, gather them up in smooth loops attached to the fork arms.

 

And it's NGC, not NCG - just saying   :->

Thank you Michael for your inputs. 

 

First, totally agree with you regarding the cables... so far a complete mess. Bu something I am about to fix today. 

 

I polar aligned with pole master and I got pretty good results (quite lower than 5 arcmins). 

 

Coming back to Starlock, as I mentioned, I am unable to recall whether the small cap (on the small sensor) was taken out. In fact, my heart is telling me that I forgot to remove it but for sure removed the bigger one. I don't know whether this could have an impact on the guiding.

 

As for the the small refractor, it's mounted on the Meade with two dovetail clamp. Will double check again.



#4 carolinaskies

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Posted 14 June 2021 - 08:38 AM

I'm not sure how good guiding via Starlock is going to be with it offset so significantly away from the main OTA.  It's possible the orthagonality of the Starlock is going to be off from the drive enough to cause the increasing drift you are noticing.   Remember Starlock is going to guide on whatever star it chooses and if it's not aligned to both DEC & RA, one or both corrective movements will result in inaccurate correction.  Normally Starlock is nestled against the main OTA at a position where it is relatively square/perpendicular to the RA/DEC.  Since you've raised it considerably away on top of another telescope this new position may be subject to misalignment.  Also, be aware of tube flexure of Starlock itself because you are no longer supporting it in the normal location but far forward.  Yes Starlock isn't 'heavy' but even a minor deviation in the tube due to weight of the sensor-package may be throwing off the proper correction by a few pixels.  


Probably you'll want to setup a testing scenario with targets N-S-E-W-Z  and see how much drift you notice in each direction.   Observatories run such setup test scenarios to perfectly dial in their systems.  

I think I would first start out using Polaris as a reference and check the 14", 80mm, Starlock(using it's focus utility) for alignment and tweak the 80/Starlock combo for centeredness over a period of hours.  Then pick a star on the Meridian and do the same, as well as a star in the far south and toward east/west horizons.  

And if possible, find a way to support the Starlock tube along the length better. 



#5 kzar

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Posted 14 June 2021 - 09:21 AM

Thank you carolinaskies for all your valid points. I didn't think about the issue that you mention with having Starlock off from the drive.... also, worth trying your recommendation, couldn't hurt :).

 

In the meantime, I was wondering if I could place the small refractor below so that it would/could solve the potential issue mentioned with the current setup. 

 

For sure, I will spend the night trying it out.... smile.gif

 

Keep you posted anyway.



#6 carolinaskies

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Posted 14 June 2021 - 09:31 AM

I've seen people mounting the bottom position. Simply make sure nothing hits and watch for cable dragging. Essentially normal stuff
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#7 kzar

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Posted 14 June 2021 - 09:39 AM

I've seen people mounting the bottom position. Simply make sure nothing hits and watch for cable dragging. Essentially normal stuff

Will take care of the cables... lol.gif looks like a real mess.



#8 kzar

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Posted 15 June 2021 - 07:25 AM

Update from my side : I placed the small refractor below the OTA and put Starlock close to its original place. In addition, I did make sure this time to take out the cap of the small sensor and make operational the HPP in Starlock after having successfully plate solve it in APT. Even though I somehow experienced some drift issues at the very beginning of the session, after doing a new calibration in APT the result is satisfying. Below is NCG 7000, without calibration (don't know what happened win APP but calibration frame did not work...need to understand why), 20x180sec.

Attached Thumbnails

  • NGC_7000_Cygnus.jpg

Edited by kzar, 15 June 2021 - 07:27 AM.


#9 carolinaskies

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Posted 15 June 2021 - 12:05 PM

If I remember there was talk a while back about whether HPP should be on or not for imaging.  As I recall it shouldn't be necessary in your scenario.  But it's easy enough to try it both ways and assess if it introduces issues.  

BTW, did you check the focus of your two Starlock cameras using the Meade Starlock utility?  Might want to double check the baseline focus to make sure neither is too far out.  



#10 kzar

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Posted 15 June 2021 - 12:26 PM

HPP couldn't/shouldn't hurt while imaging. But I would be more than interested in knowing more why it shouldn't be necessary. As for the HPP, according to Meade, thank to HPP "DSO are placed in the center of your field of view.  For normal observing, this level of precision isn't necessary.  But HPP gives you the confidence to kick off a two-hour long imaging sequence without even visually confirming a faint object's existence"

 

I didn't check Starlock focus - should to do it.



#11 carolinaskies

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Posted 15 June 2021 - 04:43 PM

HPP couldn't/shouldn't hurt while imaging. But I would be more than interested in knowing more why it shouldn't be necessary. As for the HPP, according to Meade, thank to HPP "DSO are placed in the center of your field of view.  For normal observing, this level of precision isn't necessary.  But HPP gives you the confidence to kick off a two-hour long imaging sequence without even visually confirming a faint object's existence"

 

I didn't check Starlock focus - should to do it.

As you are using APT to platesolve and then running HPP the main issue might be variance between the two systems depending on whether you initiate a GOTO through the Meade interface with HPP active. 

Remember HPP isn't a plate-solve, it's rather a comparitor position delta change of a known bright star to the catalog position of the object.  APT on the other hand is solving the region via multiple points knowing the specific vector from multiple points to center the target.  Plate-solving is far more precise in that sense which might change the location by a couple of pixels if you compare the results blinking images taken with each method.  

Definitely check the Starlock focus... it's more a checklist item for new scopes(or ones banged around alot) as some owners fail to do this and later find the focus has been out of wack causing Starlock issues. 

 




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