Re: Confusing PEMPRO Polar Alignment Sessions


Barry Megdal
 

Ray:

I definitely had APCC tracking rate correction off.  If you look at the end of my message, I did the test of turning tracking correction on, and it did a great job as indicated by PEMPRO showing almost no corrections needed.

It is a long heavy refractor, but I don't think it was still settling, as one time I tried the test twice staying on the same side of the meridian for the second test, and the results did not change.  Each test was tried 3 or 4 times, and the suggested adjustments agreed to within 10%.

What is interesting and confusing to me is that the Azimuth recommendation was essentially identical whether I used a star in the East or West, but the Altitude recommendation was very different depending on which side I did the test on.  That is what I don't understand.

I did have a dew heater on (this was the first semi-clear night we have had in Southern California in weeks, but the humidity was very high so I had no choice).  But the consistent recommended correction in altitude seems too much to be caused by air current due to a dew heater, does it not?  Not sure what drift in Dec is equivalent to say a pixel (1.12"), but I let it run for a full 5 minutes, so I would think the suggested 16 arcminutes of altitude resulted from an observed drift greater than 1/20th or even 1 pixel, but I am not sure.

I will try the field rotation test the next clear night we get.

Thanks

- Barry


---In ap-gto@..., <groups3@...> wrote :

Hi Barry,

> I tried each of the East and West tests three times, and the results were
consistent.
> PEMPRO recommended an azimuth correction of 6 arcminutes clockwise using a
> star in either the East or the West. But in the East it suggested an
altitude
> correction of about 1 arc-minute lower, while using a star in the West it
suggested I
> raise the elevation by 16 arcminutes.

>> How should I interpret this?

PEMPro can measure drift to about 1/20th of a pixel so it is very sensitive.
So the first few things that this could be:

* If you were using a heavy scope my guess is that something in the scope or
mount could be still settling after flipping.

* An accurate altitude measurement also depends on an accurate azimuth
alignment. Again, if you were using a heavy scope and it was still settling
the resulting azimuth alignment could be slightly off, which would then
influence the Altitude calculations.

* Tube currents can also cause randomness in the drift, again because
centroid measurements are extremely sensitive.

> By the way, with the APCC tracking model enabled, the recommended
corrections
> were less than 1 arcminute in az and alt, using a star in either the East
or West,
> which says good things about the model. Nonetheless, I would like to get
the polar
> alignment as close as possible.

How much field rotation are you seeing? To check this try plate solving a
few images in the far Eastern part of the sky and note the camera angle.
Flip the scope to the other side, give it time to settle then take and plate
solve more images. Compare the measured camera angles in all the images. If
they are all very close then that should give you confidence that polar
alignment is correct, provided the scope is not twisting.

-Ray Gralak
Author of APCC (Astro-Physics Command Center):
http://www.astro-physics.com/index.htm?products/accessories/software/apcc/ap
cc
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: Wednesday, January 20, 2016 11:11 PM
> To: ap-gto@...
> Subject: [ap-gto] Confusing PEMPRO Polar Alignment Sessions
>
>
>
> As part of trying to understand the APCC model created by APPM, I followed
> Roland's suggestion of trying PEMPRO with a star both to the East and to
the
> West of the meridian (with the APCC tracking correction turned off).
>
>
>
> I tried each of the East and West tests three times, and the results were
consistent.
> PEMPRO recommended an azimuth correction of 6 arcminutes clockwise using a
> star in either the East or the West. But in the East it suggested an
altitude
> correction of about 1 arc-minute lower, while using a star in the West it
suggested I
> raise the elevation by 16 arcminutes.
>
>
>
> How should I interpret this?
>
>
>
> By the way, with the APCC tracking model enabled, the recommended
corrections
> were less than 1 arcminute in az and alt, using a star in either the East
or West,
> which says good things about the model. Nonetheless, I would like to get
the polar
> alignment as close as possible.
>
>
>
> - < /span>Barry
>
>
>
>
>
>
>
> Dr. Barry Megdal
>
>
>
> Faculty
>
> D ept. of Electrical Engineering
>
> California Institute of Technology
>
> Pasadena, CA
>
> bmegdal@... <mailto:bmegdal@...>
>
>
>
>
>
>

Join main@ap-gto.groups.io to automatically receive all group messages.