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possibly tracking issue near zenith #EXOS2


Gernot Schreider
 

Hi all,

last night I was targeting M13 and did use SharpCap to do a series of photos un-attended. When inspecting the photos I found some strange effect, which looks to me like an issue with the tracking.
The photo was taken with my SonyAlpha 6000, 2min exposure time, FOV 1°x43' at 21:51 CEST, at this time M13 was  pretty close to zenith at AZ 263°, H 56°.
The mount was in tracking mode and it looks like it slewed during this time or some other effect happened.

I have  10 photos with more or less the same effect.

Has anybody seen such behavior or does anybody have an explanation what happened ?

Thanks for any help, suggestions.
Gernot


--
location: 49,55N, 7,89E; mount: EXOS-2 PMC8; telescope: Meade 8" ACF; guidescope: Orion 50mm, cameras: Sony Alpha 6000, ASI 120MC-S, laptop: Lenovo; OS: Windows 10 64bit, software: Stellarium, Sharpcap Pro, Ascom platform, AstroTortilla, DeepSkyStacker


Patrick Maher
 

Tracking at the zenith or very near the zenith with any equatorial mount is troublesome.  Even when trying to slew manually, by hand, it is very difficult to get it right.  That being said, this looks more like the mount had jerked back and forth because the scope or cables got hung up on something.  Another cause could be backlash showing more easily when near zenith because the weight is shifting from one side to the other but I think the backlash would need to be noticeably bad to result in what we see here.  

Incidentally, backlash is a routine adjustment that must be made on all tracking equatorial mounts.  This also would not be a unique problem to this particular mount.  Even if it was not the cause here, you should learn how to adjust the mount to eliminate backlash because you will need to do this adjustment at some time.  

Back to what we see in your image...  I'm leaning toward the scope or cables got jammed up on something.  If so, it would be probable that you might now also have a bit of a backlash issue to resolve.  

Patrick
--
Explore Scientific iEXOS-100 and EXOS-2GT (non-PMC)
Explore Scientific ED 102mm Refractor


W.F.
 

Hello Gernot,
an other idea is, the telescope was not right balanced.
Greetings Wolfgang


 

Gernot,
 
Whatever this is, I don't think that it has to do with your tracking *rate*.  
 
Notice the dumbbell shape of the bright star in the lower left corner?  Blob-streak-blob.  I'd interpret that as a good track, a jump, and back to a good track.  And whatever the jump was, it was quick - sudden.  You can barely see trails on M13 itself.
 
I'm with Patrick on perhaps something getting stuck, such as a cable.  You might also look for something shifting in your imaging train.  
 
But the 10 photos with the same effect is also a data point, and that makes me wonder if you (deliberately or accidentally) were using Sharpcap to dither, and just didn't get your settle time right.  You might have a look at that and if so, have a look/do a post, over on the Sharpcap forums.  
 
FWIW...
 
- Bob
 
--
Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64


Gernot Schreider
 

Thanks everyone for giving this some thinking and for your ideas.

I tend to agree that likely it has to do with the cable which connects the camera and the laptop. 
I will repeat the exercise tonight and this time I will pay close attention to cables or other possible issues.
I will update you on my findings.

Cheers
Gernot
--
location: 49,55N, 7,89E; mount: EXOS-2 PMC8; telescope: Meade 8" ACF; guidescope: Orion 50mm, cameras: Sony Alpha 6000, ASI 120MC-S, laptop: Lenovo; OS: Windows 10 64bit, software: Stellarium, Sharpcap pro, Ascom platform, AstroTortilla, DeepSkyStacker


Wade Prunty
 

This looks to me like the mount got to a position where it could no longer carry the weight, and guiding couldn't make up for the difference. I've watched this happen in real time with my iEXOS-100, and rebalancing resolved the issue. My issue resulted in subs that looked identical to this.

A cable snag would do it too, but I'm thinking that is something you would have noticed.
--
Explore Scientific iEXOS-100
William Optics SpaceCat 51 APO
ZWO ASI1600MM Pro, ASI533MC Pro
Canon 5D, T3i (Both Astro Mods)
William Optics UniGuide
ZWO ASI120MM-S
ZWO ASIAIR Pro


Gernot Schreider
 

Again Thanks everyone for comments.
I repeated the session with M13 last night and did check the setup thoroughly, especially balancing and cables and I did not see the same effect.
So it was one of the reasons mentioned, although not clear which one in particular. 
Thanks everyone

Gernot
 
--
location: 49,55N, 7,89E; mount: EXOS-2 PMC8; telescope: Meade 8" ACF; guidescope: Orion 50mm, cameras: Sony Alpha 6000, ASI 120MC-S, laptop: Lenovo; OS: Windows 10 64bit, software: Stellarium, Sharpcap pro, Ascom platform, AstroTortilla, DeepSkyStacker