Re: Problem with PEMPRO polar alignment

Ray Gralak

Joe wrote:

I get PEMPRO’s sometimes confusing target star selection, a lot as well.
Joe, the process of finding a star in PEMPro's polar alignment wizard involves:

1) Taking a full-frame (or sub-frame) image, depending on what has been configured.
2) Selecting and identifying an appropriate star within the min/max brightness range.
3) After at least two sub-frames, both of which must fall in the min/max range, PEMPro will start to show on the graph.

So, PEMPro needs to do a large full/partial frame download first then two sub-frame samples before it can make an initial trend estimate and draw the trend line you see. That can take some time depending on camera download speed, and the exposure duration.

PEMPro should *never* select bad columns as there is an algorithm for the width/height of the star, which, if any dimension is exceeded, the star is rejected.

Also, stars cannot be single width pixels (i.e. hot pixels). They automatically get rejected.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center):
Author of Astro-Physics V2 ASCOM Driver:

-----Original Message-----
From: [] On Behalf Of Joe Zeglinski
Sent: Saturday, September 19, 2020 1:55 PM
Subject: Re: [ap-gto] Problem with PEMPRO polar alignment


I get PEMPRO’s sometimes confusing target star selection, a lot as well. I was out there last night for very
many hours just to get a PEMPRO polar align on my AP-1200/CP4. There were times, when it showed “Finding
Star”, then when it seemed to have found it, responding with “ Adjusting period”, strangely, it then kept switching
back to Finding Star, several times, until it finally locked onto something. I strongly suspect, without PemPro
allowing a Dark frame to be included, it may be hitting on a vertical line of bad CCD sensor pixels, and my
camera has several. At times, I had to stop the AZ process, and click BACK, to reposition the scope to the original
align Meridian starting point, before it kept searching into the far east/west horizon, with meaningless results, if

You should check the astro sky reports, to see if the smoke in the upper atmosphere has finally cleared up in
your area. Several nights, earlier, when I initially ran polar alignment, the task was an extreme chore, really a
waste of time. It was finally better here in Ontario after a few days, and the skies are now back to fairly normal.
So, last night’s PEMPRO “Star Finding” inconsistencies were somewhat shorter – but it does work,, just requires
user patience.

Colder autumn nights will surely improve doing the alignment runs.
Joe Z.

From: maikner via
Sent: Saturday, September 19, 2020 5:16 AM
Subject: [ap-gto] Problem with PEMPRO polar alignment

I am setting up my new AP 1600 and having problem with polar align with PemPro. In step 5, the Measure
Azimuth Error, trouble finding a star and never coming up with the error measurement. I did try the slew scope
button to move a to a new field and did not solve the problem. Any suggestion??

Thank you for your help.

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