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iOptron CEM70 setup issues

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#26 Linwood

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Posted 06 December 2020 - 08:47 PM

I will try the Search Zero Position and then setting it.  I've seen that available.

I think this is really important, as I find it a bit hard by eye to judge where zero is, due to the round/square areas near the DEC axis.  RA is pretty easy -- counterweight down.  but DEC not so much.  But just search zero, get reasonably level, and see if it's not better.

 

To be fair, I rarely x-star align, just plate solve.  But search zero (and hit back to clear, do not fiddle with it) and I think you will be better.



#27 mehdymo

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Posted 06 December 2020 - 10:39 PM

This is strange! It shouldn't drift that fast even with a bad polar alignment. Tracking in PHD can change before and after meridian if the calibration is done for the opposite side and PHD can't lock it even for a few seconds. If I were you, I would tackle one problem at time and forget about zero position and Goto for now and would focus on tracking only. Check the tracking with and without guiding. 

I will try the Search Zero Position and then setting it.  I've seen that available.

 

The platesolve might get me to a target, but there is a secondary problem that I haven't mentioned here as I felt I needed to solve the root of this problem first and it might solve my secondary problem.  The second problem is, stars drift a lot.  They seem to drift so much that PHD2 cannot stay locked on a star while its setting up.  I've gone through assistance on the forums for getting phd2 setup properly with this new setup and when I set the mount to track on King rate, I have better chance at PHD2 locking in.    

 

If I am just observing through the scope, I can watch a star slowly drift out of view.  Its not super fast, and I recognize im using a longer focal length scope than I ever have before. Im using an OAG so I know its using the long focal length for the guiding and PHD2 is configured for this focal length.   I select the star to track, the star starts to drift, PHD2 is sending commands to the mounth, and after a couple minutes, PHD2 gives up as it seems the star has drifted too far.

 

So platesolve would get me to a target, but in the end, it wont get me to my goal of tracking.

 

Its clearning up, so I'll get it out again tonight and try the search zero pos.



#28 jase.wells

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Posted 06 December 2020 - 10:41 PM

I did search zero and set to the new zero. It was slightly off.  

I slewed to Mars and was fairly close.  I tried to guide off a nearby star without an alignment and I was not able to stay on the star as it kept drifting more than what PHD2 was accounting for.   I then slewed back to zero and it was off. 

 

Once capella is from behind a tree I'll align to it and start some real trials.



#29 jase.wells

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Posted 06 December 2020 - 10:44 PM

This is strange! It shouldn't drift that fast even with a bad polar alignment. Tracking in PHD can change before and after meridian if the calibration is done for the opposite side and PHD can't lock it even for a few seconds. If I were you, I would tackle one problem at time and forget about zero position and Goto for now and would focus on tracking only. Check the tracking with and without guiding. 

Really, I was going the other way. I assumed with the mount drifting as much as it is, at least I assume it is drifting more than it should, it is affecting what I can do with tracking.  Is that thought process wrong?  I spent some time on tracking last week.   I'm probably in the wrong forum for tacking assistance and might have to go back to my other thread.  


Edited by jase.wells, 06 December 2020 - 10:45 PM.


#30 mehdymo

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Posted 06 December 2020 - 10:49 PM

I think tackling the tracking is easier that the Goto because Goto, zero position, ... don't affect tracking. But, wrong information, bad alignment, and inaccurate polar alignment all affect Goto.



#31 Linwood

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Posted 06 December 2020 - 10:50 PM

Did you calibrate PHD2 near the celestial equator before trying to guide? 

 

Let's also make sure we are meaning the same thing. Tracking is what the mount does without guiding, it is primarily governed by a good polar alignment. 

Guiding is what PHD2 would give you, and while it needs a good polar alignment to do it really well, it should do a decent job once calibrated even if there are other minor issues like polar alignment (if not too severe). 

 

One useful thing in PHD2 you can try is, after calibration, turn on guiding assistant.  It will stop guiding and let the mount track while monitoring how well it is tracking.  It will then make recommendations for settings to guide better. This will also help quantify any tracking issues.

 

Also, in PHD2 make sure you have properly entered the guide scope (NOT imaging camera) info - focal length, pixel size, etc. as that is crucial to proper guiding.

 

None of this has anything to do with star alignment though. 



#32 jase.wells

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Posted 06 December 2020 - 11:05 PM

Thanks for your help.  This last time was a quick go at calibration of PHD2, but it was near mars which is near the Meridian and Celestial equator atm.  

 

Yes, I understand the difference between guiding and tracking. Apologies if I've mixed wording previously.  I'd expect tracking to be better than what I think I'm seeing. 

 

I used guiding assistant religiously with my  other mount. On the times I've locked onto a star successfully with this one, I immediately used guiding assistant. I am assuming guiding also requires relatively good tracking, not perfect, but good.  Maybe I'm wrong to assume this.

 

So my polar alignment is good. 

My zero position is re-found and re-set.

With this, my tracking should be "good" right?  

 

My next step will be to align to 1 star that I can. 

I will then go back to the celestial equator and meridian area and try to calibrate guiding. I will then look at my PHD2 logs and upload them here to share.

 

This is my first telecope with such a long focal length and my first OAG as used an external guide scope previously.  So my expectation for drift might be skewed.  I did setup the focal length, pixel size for the new OAG and guide camera.  

 

Thanks again for your help!


Edited by jase.wells, 06 December 2020 - 11:06 PM.


#33 jase.wells

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Posted 06 December 2020 - 11:35 PM

I aligned to Capella

Went to Zero

Slewed back to Capella

Took a picture of my screen at 8:33pm PT

Will go back in about 30 mins and see how much its drifted without guiding, just relying on tracking.

 

Then I will get to the guiding test.



#34 jase.wells

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Posted 06 December 2020 - 11:50 PM

So this is the drift example. Does this seem realistic/appropriate for 1645mm focal length? 

First shot taken at 8:33pm

 

 

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#35 jase.wells

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Posted 06 December 2020 - 11:51 PM

second shot only 10 mins later at 8:43

 

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#36 mehdymo

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Posted 07 December 2020 - 12:00 AM

It is high and I guess it can be reduced by more accurate polar alignment.



#37 jase.wells

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Posted 07 December 2020 - 12:43 AM

It is high and I guess it can be reduced by more accurate polar alignment.

Normally I'd agree with you, but my I polar align with software and its telling me i'm dead on.

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#38 mehdymo

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Posted 07 December 2020 - 12:53 AM

Mine was showing the same thing. Did it again and it was off! I like my polar scope more than ipolar :)

Normally I'd agree with you, but my I polar align with software and its telling me i'm dead on.



#39 jase.wells

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Posted 07 December 2020 - 01:01 AM

I just re-checked and its still polar aligned according to ipolar.



#40 mehdymo

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Posted 07 December 2020 - 02:27 AM

How is your guiding and what is your pixel scale?



#41 Linwood

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Posted 07 December 2020 - 10:51 AM

I just re-checked and its still polar aligned according to ipolar.

Did you calibrate the iPolar? 



#42 YAOG

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Posted 07 December 2020 - 11:13 AM

Geez, this seems like an easy thing to get straightened out. Obviously something is not calibrated that determines EQ tracking and GOTOs.

 

There are only a few things that determine this. Mount stability, polar alignment and tracking rate. If these items are verified orthogonlal alignment remains a possibility but this would have to be a pretty large amount of error. 

 

My guess is the mount tracking rate is set incorrectly or there is a drivetrain issue, bad stepper, slipping pulley etc. that is putting the mount off target.

 

Keep us posted, it is always interesting to see new mounts beta tested and debugged by the public. 


Edited by YAOG, 07 December 2020 - 12:10 PM.


#43 thenightinthesky

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Posted 07 December 2020 - 12:04 PM

So if we buy a Cassegrain optic we will have a bad GoTo pointing for any mount?



#44 YAOG

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Posted 07 December 2020 - 05:26 PM

So if we buy a Cassegrain optic we will have a bad GoTo pointing for any mount?

Why would that be? 



#45 mehdymo

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Posted 07 December 2020 - 06:48 PM

No, the mount pointing accuracy is a properties of the mount and doesn't depend on the scope unless the scope weight is too much for the mount to handle. The reason that you don't see the star in the field of SCT is that an SCT has a very long focal length which make the field of view very narrow.

So if we buy a Cassegrain optic we will have a bad GoTo pointing for any mount?



#46 YAOG

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Posted 07 December 2020 - 08:33 PM

No, the mount pointing accuracy is a properties of the mount and doesn't depend on the scope unless the scope weight is too much for the mount to handle. The reason that you don't see the star in the field of SCT is that an SCT has a very long focal length which make the field of view very narrow.

Hmm,

 

My first Meade LX200 8" SCT purchased new early in 1992 would 100% nail GOTOs at 133x with a 50mm AFOV 15mm Meade Super Plossl. IMO a nearly 30 years newer iOptron mount should do better easier and faster. But that's just me, YMMV.  



#47 jase.wells

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Posted 07 December 2020 - 09:24 PM

Geez, this seems like an easy thing to get straightened out. Obviously something is not calibrated that determines EQ tracking and GOTOs.

 

There are only a few things that determine this. Mount stability, polar alignment and tracking rate. If these items are verified orthogonlal alignment remains a possibility but this would have to be a pretty large amount of error. 

 

My guess is the mount tracking rate is set incorrectly or there is a drivetrain issue, bad stepper, slipping pulley etc. that is putting the mount off target.

 

Keep us posted, it is always interesting to see new mounts beta tested and debugged by the public. 

I totally agree!  I was dreaming about the tracking rate all last night. I plan on mucking with that tonight. I really hope its not a drive train issue since this is new.   I will keep you posted.



#48 mehdymo

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Posted 07 December 2020 - 09:26 PM

YAOG,

I am sure the mount is accurate, but the connections, alignment, scope mounting, etc. are not. In your case, the whole unit comes together and those errors are negligible. For example, I minimized those errors in my setup and now my IEQ45 Pro always bring the star close to center of my ASI1600 camera on a 1400mm scope. This is pretty close to magnification of 140 with a 10mm - 82 degree eyepiece. So, the mount is very accurate and its the other errors that results in inaccuracy.

Hmm,

 

My first Meade LX200 8" SCT purchased new early in 1992 would 100% nail GOTOs at 133x with a 50mm AFOV 15mm Meade Super Plossl. IMO a nearly 30 years newer iOptron mount should do better easier and faster. But that's just me, YMMV.  



#49 jase.wells

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Posted 07 December 2020 - 09:27 PM

Did you calibrate the iPolar? 

Maybe I didn't.  What is involved?  I took some darks with it when I first started with it.  After connecting, it plate solves and gives me my + and 0. I then maneuver the + to the 0 until its green.  If I missed something to calibrate it, please advise.



#50 Linwood

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Posted 07 December 2020 - 09:29 PM

Maybe I didn't.  What is involved?  I took some darks with it when I first started with it.  After connecting, it plate solves and gives me my + and 0. I then maneuver the + to the 0 until its green.  If I missed something to calibrate it, please advise.

In my CEM70 manual it's page 41.  There's a process where you set the axis at zero, and set it at 90 degrees (you can just swing it by hand).  The system compares the rotation in the two and determines the center of the camera's frame relative to the rotation axis.

 

It's worth doing, it takes all of about two minutes.




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