#### Re: Confusing PEMPRO Polar Alignment Sessions

Ray Gralak

Seems very unlikely the mount is moving in Az, but it is remote so I cannot look at
the holddowns.

I did the plate solve from images at the meridian, at hour angles of +4 and -4. At
+4 the camera angle is -0.15 degrees, and at -4 it is 0.37 degrees.
You're right is probably not Azimuth, but it could be the entire OTA tilting a little differently between the sides. Frankly, this is down to the level where it is very difficult to armchair guess exactly what's happening, but since camera angle is very slightly lopsided I would say the cause is part polar alignment error and part camera/OTA twisting/tilting.

However, I think it's so close though that it won't matter, especially if Altitude is the major concern, because the maximum effect of altitude polar alignment is at Hour angle = +/-6. Near the meridian, where usually a target is highest, the azimuth alignment error dominates and altitude alignment error almost does not matter.

-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: Thursday, January 21, 2016 11:21 PM
To: ap-gto@...
Subject: RE: [ap-gto] Confusing PEMPRO Polar Alignment Sessions

Seems very unlikely the mount is moving in Az, but it is remote so I cannot look at
the holddowns.

I did the plate solve from images at the meridian, at hour angles of +4 and -4. At
+4 the camera angle is -0.15 degrees, and at -4 it is 0.37 degrees.

What would you conclude?

- Barry

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