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Elongated Stars after Auto-Drift Align


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#1 Loden1111

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Posted 22 July 2014 - 05:49 AM

Greetings fellow LX850 weight lifters!

 

I have been the proud owner of the LX850 mount now for almost seven months. During that time I have learned intensely and have literally gone through everything in the manual several times, at a minimum. I still have an intermittant problem of some significance. First, I am probably an advanced intermediate astroimager having several serious and very productive years on an Orion Atlas with a 120mm refractor. 

 

After completing the entire initial (one star) and then drift alignment process, then PEC training, and finally the Automatic Rate Calculation, I typically get noticeably elongated stars on a ten minute exposure! :( The stars are consistently elongated E-W. 

 

Yes, I have checked all adjustments and connections to ensure there is no line drag or optic train shift. The scope and equipment is balanced in all directions. I am using the StarLock on its side-saddleplate mount, the telescope is a Celestron 1100 EDGE HD with a Celestron 0.7 reducer, and the camera is an SBIG 8300 STF-M with 8 position filter wheel.

 

There have been times when the alignment has been nearly perfect with good results but, for example, last night after going through the entire time-consuming process, I had some of the most elongated stars I have ever seen on a GEM. Before imaging, I went through the drift alignment sequence twice and the hand-paddle message was "no-turns needed" on both axises. On the nights I have gotten good results, i have needed to go back and re-do the drift alignment manually. On those nights the elevation setting was in need of noticeable adjustment. Last night as I refocused after Starlock drift alignment, I noted the focus star (at 400% enlargement) was slightly drifting upwards during the focus process. 

 

I presume that the elevation adjustment is the issue because of the E-W (RA) drift on a target just north of the equator. Notably, the difference between the one-star alignment and drift alignment in elevation settings was quite significant. After drift alignment, the scope would goto a star within an error of less than 5 arc-min using Sky-X near the equator, but had a significant error if I re-initiate setup on Polaris. The error when initializing setup on Polaris is around one degree, requiring use of the spotter scope to see Polaris. 

 

Any help would be greatly appreciated, and thanks in advance!

 

 



#2 Mark Sibole

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Posted 22 July 2014 - 08:02 PM

As im not familiar with the mount  all i can do is give suggestions.

AS with all mounts from meade in the past you need to train and calibrate the mount.This is a must.Do a pec run then do 3 itterations after that to refine pec.

Now as for your situation check to see if the star lock or anything on the mount is loose causing any dind of flexture in the system.I believe the starlock is on the mount itself.

Make sure it is seated well and tight.once that is done  make sure your OTS is seated nice and tight top help eliminate any flex there.Wit a SCT and the way the mirror dosnt lock you can get flex or mirror shift causing elongated stars.I know on the new Meade scopes they use a different morror lock system and focuser.Im not sure what the Edge uses.If the elongated stars are say 4 to 4 pixels across then id say you have a flex problem.If they are more than 5 pixels you have something going on in the drives or the alignment from my expierence.

 

I hope some of this info is helpful in figuring out where the problem lays.Keep me informed on the progress.

 

Regards

 

Mark


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Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#3 Mark Sibole

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Posted 22 July 2014 - 08:04 PM

one other thing to look at or try I always keep my scope a little off balance or weighted to the east a bit and weighted to the south.This keeps a constant pressure on the drive side of the geat eliminating and gear slop or backlash.


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Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#4 Loden1111

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Posted 24 July 2014 - 05:25 AM

Thanks Mark. I did two PEC training runs, but will do some more this evening (Wx permitting) and will shift the balance to the east and south slightly. Will also go back one more time and ensure all the bolts and screws are tightened down. There are a LOT of those bolts and hex screws on this mount, so it is always possible I missed one. The mirror does lock on this scope, and as I am using a Starlight Crayford focuser mounted on the SCT I keep the locks screwed down tight. 


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#5 Mark Sibole

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Posted 24 July 2014 - 06:44 PM

yes the focuser will keep locked but the SCT is notorious for mirror shift.Meade made improvments on later models to help lock the mirror in place but with temp changes and position of scope the mirror can still slip a bit.Im not sure how celestron does it anymore


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Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#6 Loden1111

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Posted 25 July 2014 - 11:09 AM

Mark,

 

I was up until 4:00 this morning discovering that the Auto Drift-Alignment on the LX850 really does work well and PEC error is very real. As you suspected, the PEC appears to be the majority of the problem. I initially did a manual eastern (elevation) drift check, and at a high magnification watched the target star drift west and then east, and then do it again. After four PEC training runs, the star elongation is down to about 10 pixels on an SBIG 8300 (it was about 30). I ran the guiding aggressiveness (SAS) program, but I suspect I now need to increase the RA guiding aggressiveness percentage to get the rest of the elongation out. 

 

Celestron has two mirror lock devices on the back of the scope that screw down. They must be loose to focus using the mirror, but once they are tightened down, supposedly the mirror is locked in place. I am not using the mirror focus as I have a Crayford on the scope. 

 

This 2000mm focal length imaging creates a steep learning curve for someone like me coming up from about half that. 



#7 Mark Sibole

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Posted 27 July 2014 - 06:49 AM

Good to hear you are making progress.Yes every time you do a pec run and save it it corrects more and more.And yes you have to adjust aggressiveness till you get the sweet spot.On my LX200 GPS i have it set up where with guiding i can go 30 minute sub frames with no errors at all.Things will fall into place as you learn the scope more.

I used pempro to do mine.Im not sure if your scope is covered yet but its worth looking into.It makes things real easy.

 

http://www.ccdware.c...roducts/pempro/


Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#8 Loden1111

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Posted 27 December 2014 - 05:23 AM

I don't know if anyone is still following this, but I finally found the solution to a very persistent westward drift of stars during imaging. Yes, I very carefully went through the Starlock polar drift alignment, PEC training (lost each time the mount glitches and either locks up or heads for China), tracking aggressiveness training each knight, careful attention to tightening of all connections, line drag, and probably several other drills, all to no avail. 

 

I finally adjusted the tracking rate, and after much trial and error found that by inputting a +004.750 in the Custom Tracking Rate I was able to halt the star elongation. Frankly, it just ain't supposed to be that way, but it is and at least there was a solution. 

 

Given that we ever again get a break from the overcast I will continue to test this. 

 

Has anyone else encountered this problem?

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  • Crab Nebula SBIG-C11.7 2x2 HOS 300x15.jpg


#9 Mark Sibole

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Posted 29 December 2014 - 08:37 AM

Nice image and glad you got it figured out.All scopes are different and some can be a bear to figure out.It could be anything from grease on gears not spread out to a bur to flex issues.I know on my LX200 it wasnt bad to begin with but i did regrease it and took the time to find the sweet sopt on the gear and with a few pec runs with pem pro mine tracks well for imaging over 30 minute sub frames.

Glad you got your tamed down.

Have a great new year!

 

Mark


Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#10 P-Helen

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Posted 21 January 2015 - 08:46 PM

Hi Loden, I have had this issue as well! It actually happens quite often and it has become very frustrating for me. I have gone through all of the same exact steps and procedures that you have listed above. The elevation also seems off sometimes when I go through auto drift alignment. Is it still off for you? If it is, I presume that your tracking is still good as per your solution that you have recently described. I will have to mess around with seeing my exact PEC error as well as messing with the tracking rates. As a side note, I most often see elongated stars after I do a meridian flip. Before the flip tracking is often very good, doing 15 minute subs with 2,845mm focal length and with a Sbig STT-8300M easily, but after the flip, it goes to hell. Has this been the case for you as well? At least before your final solution?



#11 Loden1111

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Posted 01 February 2015 - 07:24 PM

As it turned out the adjustment of the tracking rate only provided a short reprise. I did finally locate the problem though. It, indeed was flexure. I use a Celestron 1100 Edge HD scope (because of the Hyperstar capability) and with the Starlock in the side-saddle position there was flexure. I mounted a Vixen rail on top of the C1100 and using four Losmandy clamps, bolted together, created a saddle for the Starlock to mount on top of the OTA. After that the elongated stars were no longer a problem.

 

Thanks everyone who responded for your help. Unfortunately, one year and three weeks after purchasing the LX850, it died in mid slew. 






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