Topics

Wobbeling - can i do something about it? #EXOS2


borderbridge
 

Hi All,

I have an Exos2 PMC eight mount and an 8inch Newton on it.

Recently I started to see some Wobbling over Time( tried to do longer exposures). first i thought it might be a guiding problem so i tried without guiding. But the problem is still there

To better ilustrate what i mean i made a short video (6 seconds):

https://youtu.be/TkHyDzS8m-o

Each frame is a 30 or 45s exposure So this is happening over like 2 or three hours. But it is enough that i beginn to see it at about 60s exposures.  You can see M43 drifting downward... that is bad alignement and has nothing to to with my question. What you also see is a left and right movement . Because of that i cant do longer exposures even if i polaralign correctly. The Video without guiding so it is only the RA axis moving!

What could be the cause of this?

  • Maybe there are some parts i can check/replace?
  • Is it too much weight?
  • Or something else i can do about it?
Greetings

Manuel


 

Manuel,

Your video is a time lapse of 30-45s exposures, taken over 2 or 3 hours?

Well, you might be seeing the mount's ~600 second periodic error - that would be the side-to-side, and the drift down might be your polar alignment error showing up.  Periodic error is normal end expected - that's why we guide when doing longer exposures.

However, if you're guiding, that should correct for both of these problems and they shouldn't bother you much.  So...is your guiding ok, or not?

- Bob  



On Sun, Nov 15, 2020, at 12:51, borderbridge@... wrote:

Hi All,

I have an Exos2 PMC eight mount and an 8inch Newton on it.

Recently I started to see some Wobbling over Time( tried to do longer exposures). first i thought it might be a guiding problem so i tried without guiding. But the problem is still there

To better ilustrate what i mean i made a short video (6 seconds):

https://youtu.be/TkHyDzS8m-o

Each frame is a 30 or 45s exposure So this is happening over like 2 or three hours. But it is enough that i beginn to see it at about 60s exposures.  You can see M43 drifting downward... that is bad alignement and has nothing to to with my question. What you also see is a left and right movement . Because of that i cant do longer exposures even if i polaralign correctly. The Video without guiding so it is only the RA axis moving!

What could be the cause of this?

  • Maybe there are some parts i can check/replace?
  • Is it too much weight?
  • Or something else i can do about it?
Greetings

Manuel



--
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


borderbridge
 

Hi Bob,

Thanks for your answer! I really appreciate it.
After what you wrote i think there might be something wrong with my guiding.
I just started guiding (tried 2 nights) and noticed some "stange movements" now and then in longer exposures.
So i thought it would be a good idea to test if they are there without guiding as well. This is why i had a closer look on the movements on the images you saw in the Video.

It might very well be that just my guiding is the problem while guiding and this phenomenon is the periodic error.

Thanks a lot for the input.

The next clear night(might be a week or two) i will have a closer look on my guiding.
Guiding is still quite new to me.

Greetings Manuel

Am 15.11.2020 um 21:21 schrieb Robert Hoskin:

Manuel,

Your video is a time lapse of 30-45s exposures, taken over 2 or 3 hours?

Well, you might be seeing the mount's ~600 second periodic error - that would be the side-to-side, and the drift down might be your polar alignment error showing up.  Periodic error is normal end expected - that's why we guide when doing longer exposures.

However, if you're guiding, that should correct for both of these problems and they shouldn't bother you much.  So...is your guiding ok, or not?

- Bob  



On Sun, Nov 15, 2020, at 12:51, borderbridge@... wrote:
Hi All,

I have an Exos2 PMC eight mount and an 8inch Newton on it.

Recently I started to see some Wobbling over Time( tried to do longer exposures). first i thought it might be a guiding problem so i tried without guiding. But the problem is still there

To better ilustrate what i mean i made a short video (6 seconds):

https://youtu.be/TkHyDzS8m-o

Each frame is a 30 or 45s exposure So this is happening over like 2 or three hours. But it is enough that i beginn to see it at about 60s exposures.  You can see M43 drifting downward... that is bad alignement and has nothing to to with my question. What you also see is a left and right movement . Because of that i cant do longer exposures even if i polaralign correctly. The Video without guiding so it is only the RA axis moving!

What could be the cause of this?

  • Maybe there are some parts i can check/replace?
  • Is it too much weight?
  • Or something else i can do about it?
Greetings

Manuel



--
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


 

Manuel,

The thing about guiding is that the real measure is 'round stars', despite what the graphs say.   The graphs are a useful diagnostic tool when the stars are not round, but they're not an end in itself.

Example:  
I live in an area that typically has 'seeing' that usually doesn't get above 'average' on astrospheric and other sites.
When it's in that range, I might see 0.9<->1.1<->1.4" total RMS error, but still get round stars, although a bit fatter than I'd like.  The PHD2 scatter diagram is all over the place, because the guide star is bouncing around.  Very annoying. 

But... when the seeing clears up and the scatter diagram tightens, I can get down to 0.6<->0.7 and life is good.  I still get round stars, just a bit tighter, but I feel better about it. :-)

Lots of reasons for the graphs to do undesirable things, but when evaluating, don't forget to factor in the effects of seeing.
    
Hope this helps...

Clear skies!  

- Bob

On Sun, Nov 15, 2020, at 16:44, borderbridge wrote:

Hi Bob,

Thanks for your answer! I really appreciate it.
After what you wrote i think there might be something wrong with my guiding.
I just started guiding (tried 2 nights) and noticed some "stange movements" now and then in longer exposures.
So i thought it would be a good idea to test if they are there without guiding as well. This is why i had a closer look on the movements on the images you saw in the Video.

It might very well be that just my guiding is the problem while guiding and this phenomenon is the periodic error.

Thanks a lot for the input.

The next clear night(might be a week or two) i will have a closer look on my guiding.
Guiding is still quite new to me.

Greetings Manuel

Am 15.11.2020 um 21:21 schrieb Robert Hoskin:
Manuel,

Your video is a time lapse of 30-45s exposures, taken over 2 or 3 hours?

Well, you might be seeing the mount's ~600 second periodic error - that would be the side-to-side, and the drift down might be your polar alignment error showing up.  Periodic error is normal end expected - that's why we guide when doing longer exposures.

However, if you're guiding, that should correct for both of these problems and they shouldn't bother you much.  So...is your guiding ok, or not?

- Bob  



On Sun, Nov 15, 2020, at 12:51, borderbridge@... wrote:
Hi All,

I have an Exos2 PMC eight mount and an 8inch Newton on it.

Recently I started to see some Wobbling over Time( tried to do longer exposures). first i thought it might be a guiding problem so i tried without guiding. But the problem is still there

To better ilustrate what i mean i made a short video (6 seconds):

https://youtu.be/TkHyDzS8m-o

Each frame is a 30 or 45s exposure So this is happening over like 2 or three hours. But it is enough that i beginn to see it at about 60s exposures.  You can see M43 drifting downward... that is bad alignement and has nothing to to with my question. What you also see is a left and right movement . Because of that i cant do longer exposures even if i polaralign correctly. The Video without guiding so it is only the RA axis moving!

What could be the cause of this?

  • Maybe there are some parts i can check/replace?
  • Is it too much weight?
  • Or something else i can do about it?
Greetings

Manuel



--

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


--
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


Wes Mcdonald
 

Not sanguine the rocking is PE.  PE has a 10 minute period.  Its magnitude is +- 15-20 arc seconds.  Seems like more there. 

Wes.


--
Wes, Southport NC
EXos2-GT PMC-8, iExos 100
ES ED 127, 10" LX200GPS+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired


borderbridge
 

So any idea what it could be?

or what i could do to find out? The pattern really repeats and stays the same. Maybe that info can help.

Any sugesstion is appreciated

Greetings Manuel

Am 16.11.2020 um 00:12 schrieb Wes Mcdonald:

Not sanguine the rocking is PE.  PE has a 10 minute period.  Its magnitude is +- 15-20 arc seconds.  Seems like more there. 

Wes.


--
Wes, Southport NC
EXos2-GT PMC-8, iExos 100
ES ED 127, 10" LX200GPS+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired