7 replies to this topic

[Invator]

hi all

 

after struggling with bad star trailing on my new setup (see here); I still need to dump at least 60-70% of my subs due to high eccentricity (>0.6).
After yesterdays session I noticed that one sub showed a very wobbly satellite trail (see attachment).  This was a 120sec sub taken on LUM filter

using a ASI 294MM at -15°C. Conditions yesterday were very good, no wind, clear skies, above average seeing.  Seems to go mainly in RA direction.

 

Setup details: TS Optics 130mm Photoline refractor at native 910mm FL (1.0x flattener) on a CGEMii mount.  Guiding was very good yesterday
night using a cOAG / 174mm mini; PHD2 showed 0.5" error on average (one of the better sessions so far).  The mount is on the native tripod that
comes with the mount, standing on a thick concrete floor).

 

Questions/thoughts:

1. Anyone has seen this before?  This looks like a periodic 'wobble' in my imaging train.
2. It seems to be irregular (the other satellite trail is not that affected, also the wobbling is not consistent in the entire trail).
3. Could this be to the weight/length of the setup?  Although the CGEMii is rated up to 18kg (is this without counter weights?), the refractor
   is already at 10-11kg without imaging train (so in total I would estimate around 12 kg or so).  
4. Ever since I bought my mount, you can slightly move it (when its not powered) around the RA axis (just a slight movement), is this normal?
   Is this the backlash in the RA axis?
5. Would it be good to hypertune the mount for this?  I don't see a lot of experience around hypertuning the CGEMii (but you can buy the kit).

Attached Thumbnails

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Edited by Invator, 02 June 2021 - 01:44 AM.

[reglogge]

Maybe one of these Russian Vodka 80 satellites?

[BQ Octantis]

I captured the same thing back in '19:

 

https://www.cloudyni...ss-the-rosette/

 

They almost had me convinced that it was a gust of wind. But then that chemtrails bloke cast doubt on the whole theory.

 

Now I don't know what to believe…

 

 

BQ

Edited by BQ Octantis, 02 June 2021 - 03:17 AM.

[freestar8n]

This shows up often and if it is a long exposure it is due to gearbox noise in the tracking of the mount. 
 

There is no way the satellite could be doing that.

 

Frank

[Invator]

This shows up often and if it is a long exposure it is due to gearbox noise in the tracking of the mount. 
 

There is no way the satellite could be doing that.

 

Frank

Thanks Franck, fully agree.  This is clearly coming from the scope, but I was wondering whether this will be inherent to the setup, or something that could still be fixed (by hypertuning for example).

[Bjagastro]

I had the same experience with my IOptron CEM70. I was "lucky" enough to get two satellite tracks almost perpendicular and you can see the zig-zag which is definitely caused by high frequency oscillations (mostly in RA) of the mount created by current distortion in the micro-stepping drivers of the RA stepper motor. Also in your picture you can see that stars are elongated in the direction of the oscillation. Your wobbling has a bigger amplitude because likely the satellite was moving faster through the frame.

I excluded any other potential cause like the fan of the camera.

 

There is ample discussion on Ioptron CEM70 oscillation in this very long post. Solution was found by IOptron modifying slightly the stepper motors driver circuitry resulting in new boards to be replaced in the mount.

 

https://www.cloudyni...70-has-arrived/

 

 

 

 

 

[Invator]

I had the same experience with my IOptron CEM70. I was "lucky" enough to get two satellite tracks almost perpendicular and you can see the zig-zag which is definitely caused by high frequency oscillations (mostly in RA) of the mount created by current distortion in the micro-stepping drivers of the RA stepper motor. Also in your picture you can see that stars are elongated in the direction of the oscillation. Your wobbling has a bigger amplitude because likely the satellite was moving faster through the frame.

I excluded any other potential cause like the fan of the camera.

 

There is ample discussion on Ioptron CEM70 oscillation in this very long post. Solution was found by IOptron modifying slightly the stepper motors driver circuitry resulting in new boards to be replaced in the mount.

 

thanks - although frequency seems a lot bigger in your case (and also more constant).  I already checked impact of the fan, I don't see improvements in star shape overall (so we can rule that out).  

[freestar8n]

If you don't see the start and end of the satellite trail in an image then there is no way to know how fast it was moving through the frame - so it's hard to tell if the wiggles are caused by an oscillation many times per second vs. maybe 10 or 20 seconds.  So if it is moving fast it could be a fan instead of gearbox.

 

And if the trail doesn't actually wiggle but just varies in brightness that could indeed be the satellite spinning.

Frank