PemPro Polar Alignment differs East to West


Andrew Jones
 

Hello Everyone. I am looking for some guidance. I have a Mach 1 on a permanent pier in an observatory that I am in the process of getting setup. I currently have a 11" EdgeHD SCT mounted on the Mach 1. Last night I finally got around to getting my polar alignment dialed it. I have been using a PoleMaster to get me pretty close, but wanted to see if I could further refine the alignment using PemPro 3 since I had recently paid for the upgrade.

I started the PEMPro Alignment Wizard on the West side of the Meridian and did both the Azimuth and Altitude alignments several times until I got both under 1 arc min which was pretty much the limit of my Seeing last night. I then decided to switch to the East side of the Meridian and run the Polar Alignment Wizard again just to confirm I was aligned there as well. To my surprise I was off by quite a bit (3 - 5 arc mins) East of the meridian after letting the drift steps run for 3 - 5 mins. I didn't want to do any more adjustments as it took me several hours to get it to within 1 arc min West of the meridian. I switched back to the West and ran the polar alignment wizard again for both Az and Alt and after 5 mins both were still under 1 arc min. When I got to the step of moving the star to the end of the pointed arrow I didn't have to do anything as they were both dead on the point of the arrow. All the PEMPro 3 settings I used for where to slew in the sky where left at there defaults.

So my questions for the group is why would my polar alignment be different on one side of the meridian vs. the other? I thought once the mount is polar aligned it really should not matter which side of the Pier it is on. I have no idea why doing a pier flip to the other side of the meridian would cause such a big swing in the alignment. My only guess is that maybe my OTA is not sitting Orthogonal on the mount but I wouldn't think it would matter for drift alignment. The other thought I had is maybe I need to adjust my balance to be slightly weights heavy. Currently it is almost perfectly balanced on both axis. The Mach 1 is only about a year and half old so would not expect there to be much backlash as it has the new self adjusting gear mesh mechanism.

Needless to say, I am kind of stumped. I would welcome any knowledgeable advice on what might be going on here as I am not really sure what to do next.

Thanks in advance for the helpful advice.

Clear Skies,
Andrew J



Roland Christen
 

I went thru the same process with our remote scope in Chile several years ago. We had the polar alignment dead on with no movement in Dec for many minutes. The mount is a 1600 and scope was a 12" Mak-Cass astrograph. When we switched the scope to the other side and checked alignment on the west side, it was off, much to my amazement. In both cases the Dec axis was sitting still, not being driven. I have tried to simulate this motion via computer analysis, but no matter what changed, the alignment should remain exactly the same on either side of the axis. Even with the RA and Dec axes out of square the drift is still zero in both cases.

It then dawned on me that at the long focal length of the 12" scope, the effects of atmospheric refraction caused a small change in the star's declination. So on one side it drifts up slightly over time and on the other side it drifts down on the chip. I finally set the azimuth so that the drifts were equal on both sides rather than zero.

I might be totally wrong about this effect and its cause, but I have seen this on all the mounts that I have set up here at my observatory using PEMPRO polar alignment routine.

Rolando



-----Original Message-----
From: andrew.jones@... [ap-gto]
To: ap-gto
Sent: Sat, Mar 3, 2018 1:08 pm
Subject: [ap-gto] PemPro Polar Alignment differs East to West



Hello Everyone. I am looking for some guidance. I have a Mach 1 on a permanent pier in an observatory that I am in the process of getting setup. I currently have a 11" EdgeHD SCT mounted on the Mach 1. Last night I finally got around to getting my polar alignment dialed it. I have been using a PoleMaster to get me pretty close, but wanted to see if I could further refine the alignment using PemPro 3 since I had recently paid for the upgrade.

I started the PEMPro Alignment Wizard on the West side of the Meridian and did both the Azimuth and Altitude alignments several times until I got both under 1 arc min which was pretty much the limit of my Seeing last night. I then decided to switch to the East side of the Meridian and run the Polar Alignment Wizard again just to confirm I was aligned there as well. To my surprise I was off by quite a bit (3 - 5 arc mins) East of the meridian after letting the drift steps run for 3 - 5 mins. I didn't want to do any more adj ustments as it took me several hours to get it to within 1 arc min West of the meridian. I switched back to the West and ran the polar alignment wizard again for both Az and Alt and after 5 mins both were still under 1 arc min. When I got to the step of moving the star to the end of the pointed arrow I didn't have to do anything as they were both dead on the point of the arrow. All the PEMPro 3 settings I used for where to slew in the sky where left at there defaults.

So my questions for the group is why would my polar alignment be different on one side of the meridian vs. the other? I thought once the mount is polar aligned it really should not matter which side of the Pier it is on. I have no idea why doing a pier flip to the other side of the meridian would cause such a big swing in the alignment. My only guess is that maybe my OTA is not sitting Orthogonal on the mount but I wouldn't think it would matter for drift alignment. The other thought I had is may be I need to adjust my balance to be slightly weights heavy. Currently it is almost perfectly balanced on both axis. The Mach 1 is only about a year and half old so would not expect there to be much backlash as it has the new self adjusting gear mesh mechanism.

Needless to say, I am kind of stumped. I would welcome any knowledgeable advice on what might be going on here as I am not really sure what to do next.

Thanks in advance for the helpful advice.

Clear Skies,
Andrew J




Ray Gralak
 

Going from 1 to 3-5 arc-mins is actually not that much. Was the change mostly in azimuth, altitude, or both?

It could be that weight shift from the pier flip is causing some movement.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma

-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
Sent: Saturday, March 3, 2018 11:08 AM
To: ap-gto@...
Subject: [ap-gto] PemPro Polar Alignment differs East to West



Hello Everyone. I am looking for some guidance. I have a Mach 1 on a permanent pier in an observatory that I am in
the process of getting setup. I currently have a 11" EdgeHD SCT mounted on the Mach 1. Last night I finally got
around to getting my polar alignment dialed it. I have been using a PoleMaster to get me pretty close, but wanted to
see if I could further refine the alignment using PemPro 3 since I had recently paid for the upgrade.

I started the PEMPro Alignment Wizard on the West side of the Meridian and did both the Azimuth and Altitude
alignments several times until I got both under 1 arc min which was pretty much the limit of my Seeing last night. I then
decided to switch to the East side of the Meridian and run the Polar Alignment Wizard again just to confirm I was
aligned there as well. To my surprise I was off by quite a bit (3 - 5 arc mins) East of the meridian after letting the drift
steps run for 3 - 5 mins. I didn't want to do any more ad justments as it took me several hours to get it to within 1 arc
min West of the meridian. I switched back to the West and ran the polar alignment wizard again for both Az and Alt
and after 5 mins both were still under 1 arc min. When I got to the step of moving the star to the end of the pointed
arrow I didn't have to do anything as they were both dead on the point of the arrow. All the PEMPro 3 settings I used
for where to slew in the sky where left at there defaults.

So my questions for the group is why would my polar alignment be different on one side of the meridian vs. the other? I
thought once the mount is polar aligned it really should not matter which side of the Pier it is on. I have no idea why
doing a pier flip to the other side of the meridian would cause such a big swing in the alignment. My only guess is that
maybe my OTA is not sitting Orthogonal on the mount but I wouldn't think it would matter for drift alignment. The other
thought I had is maybe I ne ed to adjust my balance to be slightly weights heavy. Currently it is almost perfectly
balanced on both axis. The Mach 1 is only about a year and half old so would not expect there to be much backlash as
it has the new self adjusting gear mesh mechanism.

Needless to say, I am kind of stumped. I would welcome any knowledgeable advice on what might be going on here
as I am not really sure what to do next.

Thanks in advance for the helpful advice.

Clear Skies,
Andrew J






Joe Zeglinski
 

Hi Rolando,
 
    I too have seen that PemPro curve results discrepancy on runs east vs. west side of the mount.
I REALLY like your explanation, on the cause – even if the results might sometimes be slight. They could be further exaggerating with poor seeing, besides the atmospheric component adding to the discrepancy.
 
    Yes - if you run PemPro with the “standard” setting of 5 minutes  (deg ?) looking toward the east of PM, the OTA is “rising” and the atmospheric refraction is “actually improving”, all during the hour long RAW data sampling.
 
    On the flip side, running with exactly the same PemPro meridian target offset, the atmospheric refraction  can ONLY  “degrade” steadily for the entire western sky target  run.
 
    So, you have the worst of both situations. You can either trust the optimum raw data when PemPro runs from the west side of the pier on eastern targets, or the twice as bad situation with “STEADILY declining”  target Altitude ... when running with the scope on the east side (looking west).
 
    I brought this up, on this Group probably more than a couple of years ago, suggesting that PemPro could be run twice, and the two raw data curves averaged – or their samples interleaved – to come to some averaged curve result. Requires some further thinking, whether the results “should be weighted” more toward eastern targets, Something for Ray to consider, based on your premise.
 
    Anyway, Rolando, thanks for this explanation of what has been frustrating me about my own PemPro results ... for a VERY long time. Unfortunately, in the short term, we just have to live with this minor discrepancy.
 
Joe


Roland Christen
 

Hi Joe,

Thanks for your thoughts.

One could try the zenith to see if the drift in Dec is the same on either side.

By the way, I got to thinking about your daytime polar alignment routine and decided to modify it for our new mounts that have the 90 degree engraving marks on the axes. You must have the pier or tripod level for this to work. All you have to do is line up the RA and Dec engraved marks with the scope pointing to Park3 position (Home position) and tighten both sets of clutches. Then send the mount to either Park1 or Park4 and level the telescope tube assembly using the altitude adjuster.
That's it, and now all you need to adjust is the azimuth angle and that can be done by sending the scope to the Sun (with proper filter or use the ring shadow method). Turn the azimuth until the Sun lines up with the scope. You may have to move the RA axis a small amount using the E-W buttons if your keypad time is off, then press Recal. Now you are ready to slew to other bright planets or stars.

Rolando



-----Original Message-----
From: 'Joseph Zeglinski' J.Zeglinski@... [ap-gto] <ap-gto@...>
To: ap-gto
Sent: Sat, Mar 3, 2018 2:32 pm
Subject: Re: [ap-gto] PemPro Polar Alignment differs East to West



Hi Rolando,
 
    I too have seen that PemPro curve results discrepancy on runs east vs. west side of the mount.
I REALLY like your explanation, on the cause – even if the results might sometimes be slight. They could be further exaggerating with poor seeing, besides the atmospheric component adding to the discrepancy.
 
    Yes - if you run PemPro with the “standard” setting of 5 minutes  (deg ?) looking toward the east of PM, the OTA is “rising” and the atmospheric refraction is “actually improving”, all during the hour long RAW data sampling.
 
    On the flip side, running with exactly the same PemPro meridian target offset, the atmospheric refraction  can ONLY  “degrade” steadily for the entire western sky target  run.
 
    So, you have the worst of both situations. You can either trust the optimum raw data when PemPro runs from the west side of the pier on eastern targets, or the twice as bad situation with “STEADILY declining”  target Altitude ... when running with the scope on the east side (looking west).
 
    I brought this up, on this Group probably more than a couple of years ago, suggesting that PemPro could be run twice, and the two raw data curves averaged – or their samples interleaved – to come to some averaged curve result. Requires some further thinking, whether the results “should be weighted” more toward eastern targets, Something for Ray to consider, based on your premise.
 
    Anyway, Rolando, thanks for this explanation of what has been frustrating me about my own PemPro results ... for a VERY long time. Unfortunately, in the short term, we just have to live with this minor discrepancy.
 
Joe



Joe Zeglinski
 

Rolando,
 
    I think I have found the solution to solving the east-west PemPro curve difference. Simple really.
 
    Atmospheric refraction is ALREADY being taken into account by Ray’s PemPro algorithm, so it really should not be an issue here. However, if there is even some slight variation, during the target run, greater in the western part of the sky, one could very easily produce an “Averaged East-West Pier side” curve by the following procedure:
 
    Rather than settling on doing a raw data sample run for say 6 cycles – Either on one side of the pier, or on the flip side - (and ... further, assuming there are no obstructions for a “reasonable”  span on the prime meridian) – lets start pointing toward the eastern sky, by HALF the suggested (or chosen) offset angle, and let PemPro run past the meridian ending at the same offset half-angle on the western sky, to finish its LAST 3 cycles.
 
    Doing PemPro this way, the target has the SAME amount of EVER decreasing & then increasing atmospheric refraction, for the same number of cycles, split between the two sides of the pier.
 
    What might make this easier, would be if PemPro could make a note of the “actual” pre-meridian offset angle – since the user may have caused some angle delay in preparation of the run, such as the required Calibration wizardry,  and run the other HALF of the cycles until the same post-meridian angle is reached. At that point,  PemPro automatically ends itself,  in preparation for the resulting raw data curve  analysis phase.
 
    The option screen may need to be changed from choosing the number of cycles, or duration – to time or angle ahead and after crossing the meridian.
 
    I think this would be ideal.
Joe Z.


Andrew Jones
 

Hi Ray. It was pretty much the same for both Alt and Az. I ran it a couple of times and some runs it showed up to a 7 arc mins difference in Az, but pretty much stayed in the 3-5 arc min range for Alt.


Andrew Jones
 

Thanks Rolando. I appreciate the detailed reply. It is comforting to know I am in good company with this issue. :D Next chance I get I will follow your advice and split the difference in the drift between the East and West side.

Andrew J


Andrew Jones
 

Joe. Thanks for the great info. What was strange in my situation is that I actually got my best results with the scope on the East side of the Pier looking West. It was not until I switched the scope to the West side of the Pier looking East that I started to notice a much larger discrepancy.

Would you recommend starting on one side of the pier vs the other or is it a matter of just having to get both sides about the same? I am targeting to stay below 3 arc mins on both sides if possible as I seem to remember reading somewhere that 3 arc mins is kind of the minimum for long exposures. Not sure how factual that information is thou as I think it may have been something I read on CN.

Andrew J


Andrew Jones
 

Ray, why we are on the topic of PEMPro, I wanted to mention another issue I had last night. I kept getting an error last night when running step 3 of the Polar Alignment Wizard. Frustratingly it was always while taking the 3rd image in the series. The error message was "Error creating bitmap Min/Max 729/419. Parameter is not valid."

Any idea what might be causing this error? I got it both when my ATIK 16200 was connected via ASCOM directly to PEMPro and when connected via SGPro. I have never seen this error before when using SGP by itself. The only thing that seemed to allow me to get past it was to shut everything down, reboot, and then try and run it again.

If you need me to send you the log files or anything else to help investigate let me know.

Thanks for your never wavering support.

Andrew J


Ray Gralak
 

Hi Andrew,

Hi Ray. It was pretty much the same for both Alt and Az. I ran it a couple of times and some runs it showed up to a 7
arc mins difference in Az, but pretty much stayed in the 3-5 arc min range for Alt.
That may be a problem then for the refraction theory. By default PEMPro tries to account for refraction, but an East/West difference should not be evident for the Azimuth measurement. That's because the elevation of the star hardly changes during the Azimuth measurement (on East or West) and thus the refraction contribution is too small to make that much difference.

If there was a difference in the East/West refraction contribution it would most likely be in the Altitude measurement because it is usually farther away from the meridian and thus the visual elevation of the star will usually change much faster.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
Sent: Saturday, March 3, 2018 1:25 PM
To: ap-gto@...
Subject: [ap-gto] Re: PemPro Polar Alignment differs East to West



Hi Ray. It was pretty much the same for both Alt and Az. I ran it a couple of times and some runs it showed up to a 7
arc mins difference in Az, but pretty much stayed in the 3-5 arc min range for Alt.


Joe Zeglinski
 

Andrew,
 
    I don’t think it matters which pier side you start from.
As it is written now, PemPro does a continuous run, with no way of splitting it into two parts, so that we could do a half on each side, and merge the two sample files together to make say, a total 6 cycle file of raw data.
   
    Ideally, the span of cycles should be equal on both sides, since when you are finally CCD imaging, the BEST photos result from a “span” of exposures, taken either side of  the PM. You would be taking your Blue exposures before the prime meridian, and the Red ones after, where the blue in the sky diffusion tails off in the denser air. Thus, the best imaging is achieved through “planning exposures”,  that span the PM.
 
    Would be nice if the PEC curve an average matching both sides, as well. Then,  your curve accounts not only for the somewhat stochastic pattern from the small spur gears inside the gearbox, it also includes a span of the worm and worm wheel contact irregularities,  in the collected curve. End result is that it would account for  more than just the gearbox effect, in the generated PEC curve.
 
    However, another problem would arise if I were to do a PemPro run, “right through” the meridian.
If the scope is “TOO perfectly” balanced, there may be some very minor worm tooth “gear play” during the transition ...  causing a slight lag as the mount passes PM. Or, there could be a “loading change” on the worm/worm wheel,  and the gears in the box, if the OTA is (purposely)  slightly biased, off-balance. Either one could (perhaps)  cause PEC curve inaccuracies depending on which side of the pier you are shooting from.
 
    It would be ideal to actually perform a Meridian Flip after half the number of cycles – then have PemPro “Resume” the remaining raw data collection cycles. But, that is not possible with the present program method.
Either way – running right through PM, or “resuming” after a flip, would produce data that may be closer to a true “average cycle” for the ideally used CCD imaging span,  across the PM.
 
    Next time, I think I will go for the continuous PemPro right across the PM, and “trust” that this provides better results.
 
Joe


Ray Gralak
 

Ray, why we are on the topic of PEMPro, I wanted to mention another issue I had last night. I kept getting an error last
night when running step 3 of the Polar Alignment Wizard. Frustratingly it was always while taking the 3rd image in the
series. The error message was "Error creating bitmap Min/Max 729/419. Parameter is not valid."

Any idea what might be causing this error? I got it both when my ATIK 16200 was connected via ASCOM directly to
PEMPro and when connected via SGPro. I have never seen this error before when using SGP by itself. The only thing
that seemed to allow me to get past it was to shut everything down, reboot, and then try and run it again.
I think you should check that the .Net Framework 4.x is up to date. That error can only happen when creating a normal 32-bit Bitmap in the .Net Framework.

Also make sure you have binning set to 1 on step 2 just in case a binned image might be causing a problem.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma


-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
Sent: Saturday, March 3, 2018 2:05 PM
To: ap-gto@...
Subject: [ap-gto] Re: PemPro Polar Alignment differs East to West



Ray, why we are on the topic of PEMPro, I wanted to mention another issue I had last night. I kept getting an error last
night when running step 3 of the Polar Alignment Wizard. Frustratingly it was always while taking the 3rd image in the
series. The error message was "Error creating bitmap Min/Max 729/419. Parameter is not valid."

Any idea what might be causing this error? I got it both when my ATIK 16200 was connected via ASCOM directly to
PEMPro and when connected via SGPro. I have never seen this error before when using SGP by itself. The only thing
that seemed to allow me to get past it was to shut everything down, reboot, and then try and run it again.

If you need me to send you the log files or anything else to help investigate let me know.

Thanks for your never wavering support.

Andrew J


Suresh Mohan
 

To overcome this problem i use a star at 45 degrees or slightly above as I live on a hot sea coast where atmosphere sizzles . It might take a little longer but it gets accurate ( however I use a refractor )


On 04-Mar-2018, at 2:01 AM, 'Joseph Zeglinski' J.Zeglinski@... [ap-gto] <ap-gto@...> wrote:

 

Hi Rolando,
 
    I too have seen that PemPro curve results discrepancy on runs east vs. west side of the mount.
I REALLY like your explanation, on the cause – even if the results might sometimes be slight. They could be further exaggerating with poor seeing, besides the atmospheric component adding to the discrepancy.
 
    Yes - if you run PemPro with the “standard” setting of 5 minutes  (deg ?) looking toward the east of PM, the OTA is “rising” and the atmospheric refraction is “actually improving”, all during the hour long RAW data sampling.
 
    On the flip side, running with exactly the same PemPro meridian target offset, the atmospheric refraction  can ONLY  “degrade” steadily for the entire western sky target  run.
 
    So, you have the worst of both situations. You can either trust the optimum raw data when PemPro runs from the west side of the pier on eastern targets, or the twice as bad situation with “STEADILY declining”  target Altitude ... when running with the scope on the east side (looking west).
 
    I brought this up, on this Group probably more than a couple of years ago, suggesting that PemPro could be run twice, and the two raw data curves averaged – or their samples interleaved – to come to some averaged curve result. Requires some further thinking, whether the results “should be weighted” more toward eastern targets, Something for Ray to consider, based on your premise.
 
    Anyway, Rolando, thanks for this explanation of what has been frustrating me about my own PemPro results ... for a VERY long time. Unfortunately, in the short term, we just have to live with this minor discrepancy.
 
Joe


Andrew Jones
 

Ray.

 

If my PEC Curve is out of date could this account for some of the variation between the East and West side? I still have the factory PEC Curve on my Mach 1. Getting into the PEC module of PEMPro is on my to-do-list once I get my polar alignment dialed in. I would also like to use APPM a create a sky model, but again wanted to wait until I got the polar alignment dialed in first. Would you recommend checking/updating the PEC before creating the sky model? I assume the answer is yes, but just wanted to confirm.

 

So much to do, so few clear nights…

 

Thanks again for all your support.

 

Andrew J


Ray Gralak
 

Hi Andrew,

Would you recommend checking/updating the PEC before creating the sky model? I
assume the answer is yes, but just wanted to confirm.
It won't matter to any significant amount if you update PEC before or after building a sky model.

Best regards,

-Ray Gralak
Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc
Author of PEMPro: http://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver
Author of PulseGuide: http://www.pulseguide.com
Author of Sigma: http://www.gralak.com/sigma

-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
Sent: Sunday, March 4, 2018 6:59 PM
To: ap-gto@...
Subject: [ap-gto] Re: PemPro Polar Alignment differs East to West



Ray.



If my PEC Curve is out of date could this account for some of the variation between the East and West side? I still
have the factory PEC Curve on my Mach 1. Getting into the PEC module of PEMPro is on my to-do-list once I get my
polar alignment dialed in. I would also like to use APPM a create a sky model, but again wanted to wait until I got the
polar alignment dialed in first. Would you recommend checking/updating the PEC before creating the sky model? I
assume the answer is yes, but just wanted to confirm.



So much to do, so few clear nights.



Thanks again for all your support.



Andrew J