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Paramount ME makes oblong stars, works better w/o PEC ?

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#1 Mark Bailey

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Posted 07 January 2020 - 02:13 AM

I have a TEC 140 on a Paramount ME with a SBIG ST-10XME. Lately I have been getting particularly disappointing results and wrestling with nearly every component in the complex system.

 

Taking one problem at a time, recently I have been focused on trying to get my big expensive mount to do 10 minute unguided subs. According to Software Bisque's T-Point claims, that should be easily doable with a 1000mm focal length.

 

But I have been getting quite oblong stars unguided for five and ten minutes, although ten minutes no worse than five.

 

I am using TheSkyX Pro.

 

The mount is on a cement pier inside an observatory dome and the polar alignment is ranked good in T-Point. My setup's image scale is 1.43 arcsecs/pixel.

 

I recently re-lubed the mount as illustrated in the online video "Lubricating the Mount by Software Bisque." In T-Point I ran a 330 point session and ran the super model to get Sky RMS = 9.3 and PSD = 9.7. Quite good I think. Protrack is activated and enabled. I also ran a periodic error training as per Richard Wright's "Training Periodic Error (PEC) on Paramounts" video. The results were poor. A 20 minute log training session with PEC off gave me a 4.2 arc seconds peak to peak fitted curve. I saved that to the mount for PEC and ran another session with PEC turned on and the results were somehow worse at 5.9 arcsecs peak to peak.

 

None of these efforts helped my oblong stars.

 

I have a long thread going now on Software Bisque's forum here. There was a question about orientation of the scope or possible mirroring of the image for the PEC training runs. An image was checked and they are not mirrored. Tonight, with better seeing than recently, I created some new autoguiding PEC training logs as per Richard Wright's video. As per the video I am using my primary scope and camera as the autoguider. Log 1 was taken east of the meridian with a LUM filter, one second exposures, for about 20 minutes and with "Apply PEC" not checked, i.e. with PEC off. It plotted out at 4.1 arcsecs peak to peak.Still in the east, still near 0 degrees declination, log 2 was made with log 1 saved to the mount for PEC and PEC turned on. It plotted out to 7.8 arcsecs peak to peak! Not as it should be. Makes no sense. It could be that the correction was being applied upside down as it were. I went ahead and tried the reverse where a box in the Bisque Telescope Control System is checked that the scope was pointing west (even though it was pointed east). With PEC turned on log 3 plotted out at 7.7 arcsecs peak to peak.

 

Good grief.

 

I considered giving the mount a breathalyzer test.

 

I went through the whole process again. Same results. No PEC = 4.2 arcsecs peak to peak. With PEC turned on twices as bad at 8.0 arcsecs peak to peak. With PEC and west box checked, 8.1 arcsecs.

 

In other words, the PE is better (but not good) when PEC is turned off.

 

That begged the question of what does a long exposure look like with PEC turned off. I had not tried that before. With a lot of moon out tonight I used an Ha filter and focused with that filter using @focus3. A 60 second exposure looked pretty good! The stars may be a little fat but they were round with a FWHM measure of 3.4. I think that is in pixels so at 1.4 arcsecs/pixel in my camera, pretty fat. But round. 300 seconds measured 3.4 also. 600 seconds were starting to become oblong but much better than it had been and a FWHM of 4.5. This is much better than I was getting unguided with PEC turned on.

 

This big, expensive mount should do better and it is odd to say the least that it works better with PEC off.

 

I'd love to hear anybody's thoughts.

 

Mark


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#2 BKMaynard

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Posted 07 January 2020 - 03:01 AM

That’s a tough one. I have an MX+. I’ve had some pec training that yielded worse results and waited for better seeing conditions. 10 min is doable but I have to toss out 30-40% of the subs
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#3 MikiSJ

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Posted 07 January 2020 - 03:17 AM

I had a Paramount ME for two years in the late oughts with an APM 152/1200 and I always guided. I also ran PEC and the error was consistently insignificant. I would do a 50 star PEC run once a month and was always fascinated watching the mount move back and forth, back and forth and back and forth.

 

I personally believe that letting a mount, even as good as the ME is, do its own thing is tossing a coin and hoping that you didn't waste 10 minutes to get oblong stars.


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#4 Mark Bailey

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Posted 07 January 2020 - 08:37 AM

That’s a tough one. I have an MX+. I’ve had some pec training that yielded worse results and waited for better seeing conditions. 10 min is doable but I have to toss out 30-40% of the subs

Thanks. That is good to know although disappointing to learn about these mounts.

 

 

I had a Paramount ME for two years in the late oughts with an APM 152/1200 and I always guided. I also ran PEC and the error was consistently insignificant. I would do a 50 star PEC run once a month and was always fascinated watching the mount move back and forth, back and forth and back and forth.

 

I personally believe that letting a mount, even as good as the ME is, do its own thing is tossing a coin and hoping that you didn't waste 10 minutes to get oblong stars.

Also good to know, thanks.I like to use CCDAutoPilot and autoguiding has been slowing that routine down. For some reason it has to plate solve to re-acquire the guide star between half the frames or more. I was hoping to lose the one-more-thing-to-go-wrong complexity of autoguiding but may have to delve into it.



#5 maxmir

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Posted 07 January 2020 - 08:54 AM

You need PE to be very low,  near your seeing limit. 1.5 arcseconds or less to do unguided imaging.

Otherwise you will see elongation in RA in one worm cycle.

 

I have a ME. I gave up on protrack years ago after many failed tests.

I was able to get PEC to 1 to 1.5 arcseconds but the best I protrack could do was 5 mins in all regions of the sky.

 

You may get near 10min since your focal length is shorter.

I had to buy a newer mount with encoders to get this kind of unguided performance.

Sometimes it is easier to guide.


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#6 Ishtim

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Posted 07 January 2020 - 08:58 AM

Mark,

I read the discussion here as well as on the SB site. 

I've had a permanently mounted ME in service for over 15 years with various OTAs and SBIG cameras so I'll offer my :penny: :penny: .

 

You mentioned doing a re-lube, did you strip the mount down to do this?  (e.g. remove OTA, counterweight bar, etc)

I ask because it is possible that your setup's balance is now "off" and this can/will create oblong stars as well.

As for PEC and training the mount, I still run TheSky6 so I cant speak specifically to TSX and it's PEC routines, but I'll add that I abandoned PrecisionPEC (SB's original PEC solution for the ME) because of it's complexity and odd results like what your getting and I ended up going with CCDWare's PEMPro which basically "holds your hand" through the process.  In all I think I have trained and applied PEC 3 times over the years and haven't touched it since the last time I took the mount on a road trip and completely realigned everything. 

 

I understand the struggle (been there, done that) and completely agree that 5-10min unguided subs with the ME are achievable at 1000mm FL, but guiding makes life so much easier, especially since your SBIG ST-10XME is capable of self-guiding you really don't need to add gear unless you are trying to guide thru narrowband filters. 


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#7 Mark Bailey

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Posted 07 January 2020 - 09:00 AM

Sometimes it is easier to guide.

Thanks, maxmir, this is very useful and enlightening feedback. Do you run with ProTrack off or just not rely on it? -Mark
 



#8 Mark Bailey

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Posted 07 January 2020 - 09:09 AM

Mark,

I read the discussion here as well as on the SB site. 

I've had a permanently mounted ME in service for over 15 years with various OTAs and SBIG cameras so I'll offer my penny.gifpenny.gif .

 

You mentioned doing a re-lube, did you strip the mount down to do this?  (e.g. remove OTA, counterweight bar, etc)

I ask because it is possible that your setup's balance is now "off" and this can/will create oblong stars as well.

As for PEC and training the mount, I still run TheSky6 so I cant speak specifically to TSX and it's PEC routines, but I'll add that I abandoned PrecisionPEC (SB's original PEC solution for the ME) because of it's complexity and odd results like what your getting and I ended up going with CCDWare's PEMPro which basically "holds your hand" through the process.  In all I think I have trained and applied PEC 3 times over the years and haven't touched it since the last time I took the mount on a road trip and completely realigned everything. 

 

I understand the struggle (been there, done that) and completely agree that 5-10min unguided subs with the ME are achievable at 1000mm FL, but guiding makes life so much easier, especially since your SBIG ST-10XME is capable of self-guiding you really don't need to add gear unless you are trying to guide thru narrowband filters. 

Andrew- very kind of you to walk through all this with me. I will take a look at PEMPro. And no, I did not tear down the mount at all, just removed the worm gear cover plates. Good point though. I can never get the internal guider on my SBIG to calibrate so I use SBIG's remote guidehead on an 80mm Orion ST80.  I mentioned above that autoguiding is slowing down my CCDAutoPilot sessions but I may just have to be patient and/or troubleshoot that issue with CCDAutoPIlot's developer, who is usually helpful. -Mark
 



#9 Allaboutastro

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Posted 07 January 2020 - 10:20 AM

Mark:

 

A couple of questions...

 

- Are you getting the same elongation when autoguiding with the guidescope?  

 

- Is ProTrack activated when doing the PEC?  

 

- By what method are you locking down your axes and have you experimented with your backlash settings?   

 

- What type of camera connection are you using?  How is the guidescope mounted? 



#10 MikiSJ

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Posted 07 January 2020 - 01:59 PM

You mentioned doing a re-lube, did you strip the mount down to do this?  (e.g. remove OTA, counterweight bar, etc)

Although it has been over 10 years since I owned a ME, I seem to recall the manual said that it was necessary to disassemble the R&P when re-lubing.

 

I could be mistaken because I seldom RTFM.


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#11 Mark Bailey

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Posted 07 January 2020 - 04:16 PM

Mark:

 

A couple of questions...

 

- Are you getting the same elongation when autoguiding with the guidescope? 

Hi Jay- Not that I have noticed. Focusing has been a challenge but autoguided captures have round stars. If you mean did I run a log using guidescope to check on periodic error, then no, I didn't try that.

 

- Is ProTrack activated when doing the PEC? 

Yes, it is. I wondered about that, but it was on all the time, including when I was capturing uncorrected periodic error.

 


- By what method are you locking down your axes and have you experimented with your backlash settings?   

I don't know enough about these issues to answer the question. Are there backlash settings somewhere?

 

 


- What type of camera connection are you using?  How is the guidescope mounted? 

The camera is mounted on an Optec rotator which mounted on an Optec IFW. Here is a pic. I am not using the cooling hoses any more. The guidescope is mounted on rings in a rigid plate mounted directly to the ME and parallel to the main scope.

 

-Mark

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#12 Allaboutastro

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Posted 07 January 2020 - 06:01 PM

Mark:  

 

I want to eliminate any possible variables, but more importantly tailor the advice based on what's on hand.  

 

Point by point...

 

-  I asked about the autoguider because I wanted to know if it's an option (at which point we wouldn't have to obsess about perfection.   Plus, I wanted to know if you were seeing elongations...to rule out differential flexure SHOULD you want to autoguide.  

 

- Do PEC first, then ProTrack.   Don't activate ProTrack until later...and in fact, you should be able to get your goal of unguided images even without ProTrack.   Do an initial calibration runs in T-Point to assure dead accurate pointing first...and in fact, if your T-Point model is missing object slews, then ProTrack isn't going to get good data to work with.  Just because the model is 330 points doesn't mean it's accurate.  How accurate is your T-Point model?

 

- The Paramount ME can be sloppy (especially in RA) if the worm and gear aren't properly engaged, which means turning the knobs not too tight (which causes stiction) and not too lose (with causes backlash).   TheSkyX has a backlash compension setting (check out the autoguide graphs and right click to get "real time" data, which lets you adjust backlash and guiding aggressiveness on the fly).    You shouldn't need to adjust backlash if the gear/worm is properly engaged...but I wondered if you had played with it?   Anyway, the RA & DEC knobs...tighten them all the way and back off a quarter turn...this might insult your intelligence, but we shouldn't assume that you knew to do it! 

 

-   How is the filter wheel connected in your picture?  Are those set-screws or a threaded connection?  It could explain the elongation...probably not, but I want to rule it out.  

 

- Make sure any modelling and PEC is done after the relube.   You probably knew that...just wanted to state it.  

 

- Andrew mentioned PEMPro...and that's the way I do PEC.   I like it because it averages out the seeing over multiple worm cycles.  I'm not sure if "Richard's method" does that?  I haven't ever done it that way myself.   But if not, you really want to make sure seeing is stable before doing a PEC run...more importantly, make sure the scope is cooled down and the entire area is equalized in temperature.  I like to use a box fan around my instruments to assure air is moving and eliminating any temperature zones that can cause unstable images...especially when doing PEC.   

 

You should be able to get your mount easily under an arcsec of error immediately after PEC...which is likely better that you can autoguide.  At that point, assuming no drift (use early and separate T-Point models to REALLY nail down the polar alignment), then you should be able to do unguided imaging easily at that focal length.   

 

ProTrack comes in handy when you want to do unguided imaging with even more precision, like with 2500mm instruments or so.  I wouldn't even bother with it...and typically don't. 

 

EDIT:   The backlash compensation settings might be under the guider calibration menus...I'm going by memory there, and it's not all that good today!  LOL


Edited by Allaboutastro, 07 January 2020 - 06:05 PM.

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#13 Mark Bailey

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Posted 07 January 2020 - 08:01 PM

Jay, thank you for your very generous response. I will admit I did the big TPoint model remotely from Salt Lake because I could. Then I went down to Torrey and lubed the mount when schedule permitted. I will run another model. I might have to wait for the moon to get a bit out of the way.  The TPoint numbers were good, Sky RMS = 9.3 and PSD = 9.7. I am back in Salt Lake now and can't look but I believe the filter wheel has a 2"tube that goes into the TEC 140's compression fitting. I think the RA and DEC knobs are adjusted about right but I will look into the backlash routine you mentioned.Then some good seeing with a well aired out observatory and a try with PEMPro without Pro-Track and see what I get. -Mark



#14 Mark Bailey

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Posted 14 January 2020 - 10:20 AM

Success with PEC.

 

It turns out that for older mounts like mine with older controller boards the mount must be power cycled after a PE log is loaded to the mount in order to take effect. The procedures have changed with recent software and that step is no longer mentioned. Had I dug deep enough into the instructions for obsolete procedures I would have seen that step. Finally an experienced guy on the Software Bisque forum mentioned it.

 

Thanks again CN for your enthusiastic help and support.

 

Onward,

 

Mark


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#15 Ishtim

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Posted 14 January 2020 - 10:37 AM

Glad you got it figured out AND thanks for sharing your findings!


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#16 Allaboutastro

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Posted 14 January 2020 - 11:27 AM

Glad to hear, Mark.   Which control board does yours have?   I'm assuming MKS3000 in that case.  If memory serves, you needed at least that to make use of ProTrack. 


Edited by Allaboutastro, 14 January 2020 - 11:28 AM.


#17 Mark Bailey

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Posted 14 January 2020 - 11:34 AM

Glad to hear, Mark.   Which control board does yours have?   I'm assuming MKS3000 in that case.  If memory serves, you needed at least that to make use of ProTrack. 

I am not sure but it is likely the MKS3000. Apparently the MKS4000 needs to by power cycled too. And thanks for the reminder about ProTrack, I will have to check to see if I left it off!

 

Jay, thanks for your generous help. I think I now have the old mount tuned up and operating well within spec. At 63 I am always delighted when the old things still work just fine.

 

Mark
 



#18 Allaboutastro

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Posted 14 January 2020 - 01:53 PM

Mark:   

 

My main Paramount ME has the MKS4000 and I've never needed to power cycle to get the PEC to take.  Strange.  I think our other ME is the MKS3000, but I haven't done PEC with it since it's hasn't really been in service yet.   You've definitely given me something to watch out for now!    Your remarks have made me curious, so I'm definitely going to look more deeply into this myself!   Thanks for your hard work on all of it!!!

 

EDIT:   I've always used PEMPro for the PEC programming...so perhaps that's been the reason for my success?   Hmmm.


Edited by Allaboutastro, 14 January 2020 - 01:54 PM.

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#19 Ishtim

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Posted 14 January 2020 - 04:00 PM

Since PEC training isn't something I've had to do very often and after reading Mark's response, I looked back at the ME User's Guide to review the procedure.  The recommendation for at least TheSky6 users is to buy/use SB's PrecisionPEC, then a few lines later on page 65 (in ver. 1.79), Recording Corrections, step 6 states: "The power on the Paramount ME must be cycled before the new periodic error corrections take effect."

waytogo.gif



#20 Mark Bailey

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Posted 14 January 2020 - 04:37 PM

Since PEC training isn't something I've had to do very often and after reading Mark's response, I looked back at the ME User's Guide to review the procedure.  The recommendation for at least TheSky6 users is to buy/use SB's PrecisionPEC, then a few lines later on page 65 (in ver. 1.79), Recording Corrections, step 6 states: "The power on the Paramount ME must be cycled before the new periodic error corrections take effect."

waytogo.gif

I wish I had kept reading the ME guide back when I started on this issue. The stumbling block for me was that SB no longer supports PrecisionPEC and I have TheSkyX Pro so the manual was describing obsolete software I didn't have and I looked for solutions elsewhere. Nonetheless, there would have been a major clue to my PEC problem if I had kept reading. All in the art, and hard knocks, of problem solving.

 

Mark
 


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#21 Allaboutastro

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Posted 14 January 2020 - 05:27 PM

I remember needing to power cycle in TheSky6...but using TheSkyX over the recent umpteen years it hasn't been an issue on the MKS4000 version using PEMpro, which I use to copy the PEC curve to the clipboard and paste within TheSkyX.   I know it's worked for me without power cycling because I always reactivate that curve and run PEMpro a second time to test the results.  

 

Even so, I'm going to review all those procedures just to verify everything is optimal.  


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#22 csauer52

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Posted 14 January 2020 - 08:51 PM

Great topic to read, thanks for sharing this information.

 

Super curious to know how well the PEC is working now. Are you able to image unguided and if so, for how long?


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#23 Mark Bailey

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Posted 14 January 2020 - 09:32 PM

Great topic to read, thanks for sharing this information.

 

Super curious to know how well the PEC is working now. Are you able to image unguided and if so, for how long?

Thanks, Csauer. The final results I got in the corrected PE curve was 0.4 arcsecs peak to peak. The goal was to get under 1 arcsec. So great results. Seeing was a 1 out of 5 last night and focusing was off. But I had nice round if somewhat fuzzy stars unguided at 10 minutes. (tonight the rotator got tangled up and more results will have to wait until I am again on site in a few days or so.)
 


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#24 Allaboutastro

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Posted 14 January 2020 - 09:50 PM

Thanks, Csauer. The final results I got in the corrected PE curve was 0.4 arcsecs peak to peak. The goal was to get under 1 arcsec. So great results. Seeing was a 1 out of 5 last night and focusing was off. But I had nice round if somewhat fuzzy stars unguided at 10 minutes. (tonight the rotator got tangled up and more results will have to wait until I am again on site in a few days or so.)
 

Loving that!   Congrats on figuring it out!   


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