Re: Adjust CP4 Clock Frequency


Ray Gralak
 

Steve,

Many AP clients doing photometry REQUIRE that kind of 1 arc-sec precision and it seems achievable with the
right approach. A number of us would like to know more about how to achieve it. Dithering is not an option in
photometry. Craig's posts bring up significant points that are quite relevant and should be considered seriously.
For photometry you could use APCC Pro's tracking rate correction and auto-guiding. This is better solution because auto-guiding will
update mount position more imminently than waiting longer for an image to complete and be plate solved. The drawback of Craig's
plate solve method is that it corrects after the tracking error has occurred. So, if a plate solve indicates a correction is
required then Craig's software may have already gone outside 1-arcsec accuracy.

Auto-guiding + APCC Pro tracking rate correction is definitely capable of sub arc-second tracking over many hours. And with a couple
tweaks to the code APPC Pro's tracking rate could be constantly refined to match any residual tracking rate error calculated from
snooping auto-guide pulses sent to APCC.

But again, this is not the subject of this thread!

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver


-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Steven Steven
Sent: Wednesday, May 6, 2020 1:53 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Ray,
Many AP clients doing photometry REQUIRE that kind of 1 arc-sec precision and it seems achievable with the
right approach. A number of us would like to know more about how to achieve it. Dithering is not an option in
photometry. Craig's posts bring up significant points that are quite relevant and should be considered seriously.

Steve

________________________________

From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Ray Gralak <groups3@gralak.com>
Sent: Wednesday, 6 May 2020 10:50 AM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Hi Craig,

So if I understand correctly, using your scope, unguided, and with APCC corrective tracking, you can plate solve
your first image, three hours later plate solve your last image and the difference in plate solutions is less than 1
arc-sec?
No, I'm not saying that at all, although I'm sure under some conditions that would be possible.

What I'm saying is most people would not want to do that. Most want to randomly dither the telescope position
between images to average out differences in pixel sensitivity and noise when stacking images. Dithering
obviously will change the image center between images. And cases where low pixel resolution (e.g. camera lens)
dithering can be used to increase effective detail in an image.

So acceptable unguided performance is needed only for the duration of the longest exposure. There's little
advantage for tracking to be better than that, but it's great that you are able to do that via a closed loop process.

Anyway, hopefully you can try Roland's test so you can validate your mount's sidereal tracking rate.

-Ray Gralak
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro <https://www.astro-
physics.com/apcc-pro>
Author of PEMPro V3: https://www.ccdware.com
Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver
<https://www.siriusimaging.com/apdriver>

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Craig Young
Sent: Wednesday, May 6, 2020 7:02 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Ray,
So if I understand correctly, using your scope, unguided, and with APCC corrective tracking, you can plate solve
your first image, three hours later plate solve your last image and the difference in plate solutions is less than 1
arc-sec?

Craig




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