Re: Mount coordinates change while autoguiding


Michael Dolenga
 

DOH! I completely forgot about the collimation screws. I installed it in the mount ages ago and it's been there ever since. 

That said, given that I usually shoot from either my lumpy, mole infested backyard or remotely, guaranteeing good levelling isn't always the case. The extra validation from Sharpcap is helpful.

Michael


On Tuesday, July 21, 2020, 11:49:57 AM PDT, uncarollo2 <chris1011@...> wrote:



Back in RAPAS, Polaris was noticeably out of place.
Yes, and then you adjust the RAPAS via the 3 collimation screws to put Polaris where it should be, and then you have a RAPAS that can recreate that perfect polar alignment in about 10 seconds next time you set up. That's the whole idea about the collimation screws on the RAPAS.

Rolando


-----Original Message-----
From: Michael Dolenga via groups.io <giroditalia@...>
To: main@ap-gto.groups.io
Sent: Tue, Jul 21, 2020 1:44 pm
Subject: Re: [ap-gto] Mount coordinates change while autoguiding

I got the Polemaster camera, and used it with SharpCap. After careful alignment with the RAPAS, sharpcap reported an error of about 5 arcminutes, which it categorizes as "poor." A few minutes with the app and it was down to 11 arc seconds error. Back in RAPAS, Polaris was noticeably out of place. The imaging session I did last night showed at most 5 arc seconds of drift per hour over a 4 hour period, so clearly there was an improvement, although that's anecdotal at best. And I don't see any improvement on the images, I think we're seeing limited here in Seattle. Actually, cloud limited. :)

Michael



On Saturday, July 18, 2020, 09:39:18 AM PDT, uncarollo2 <chris1011@...> wrote:



Btw, is a 1 minute DEC drift over 1 hour at a declination of about 40 degrees good/bad?
The mount itself doesn't move in Dec, so all drift is due to external errors (atmospheric refraction, differential flexure, polar misalignment). Most Dec drift is simple polar misalignment in azimuth when pointing overhead and altitude misalignment when pointing towards the east or west.

Is 1 minute drift good/bad - I think that's bordering on excessive and can be easily fixed using PEMPro drift alignment. Good alignment back in the "good ol' days" was 1 arc sec drift per 5 minutes. That's back in my day when we used to walk uphill to school thru 5 foot snow drifts, and uphill again home.

Rolando


-----Original Message-----
From: Michael Dolenga via groups.io <giroditalia@...>
To: main@ap-gto.groups.io
Sent: Sat, Jul 18, 2020 11:27 am
Subject: Re: [ap-gto] Mount coordinates change while autoguiding

You do need to recalibrate after flipping to account for orthogonality errors. And you'd have to slew to the same coordinates reported by the mount just before you flip, which differ from the target. It's not really an issue once you understand what is happening, and luckily the software I'm using, NINA, does a plate solve after flipping and re-slews, if necessary, to your original target coordinates which it has preserved. I raise the question because until I understood how NINA worked, I thought the drift on the mount was problematic.

When I was doing flips manually, I would calibrate before flipping to reset the mount's coordinates to match my target, as Ray suggested.

Btw, is a 1 minute DEC drift over 1 hour at a declination of about 40 degrees good/bad? 1850 mm scope. Polar aligned using RAPAS.


Michael



On Saturday, July 18, 2020, 09:06:43 AM PDT, uncarollo2 <chris1011@...> via groups.io <chris1011@...> wrote:



The meridian flip automation i use includes a re-centering of the target via plate solve, which I think is pretty common
When you are autoguiding the target is always centered so no plate solve is needed. Because of the guide commands, the internal co-ordinates slowly drift, so at the end of the session you simply do a recal which brings the actual and commanded co-ordinates back together.

Rolando


-----Original Message-----
From: Brian Valente <bvalente@...>
To: main@ap-gto.groups.io
Sent: Sat, Jul 18, 2020 10:52 am
Subject: Re: [ap-gto] Mount coordinates change while autoguiding

>>> If I leave the mount running with no autoguider connected at all, RA and DEC remain constant, as I would expect. 

But likely the fov would have change significantly, so your target would have drifted out of frame

 >>>This confounds automated meridian flips because the mount "thinks" it is pointed somewhere other than where it actually is. Often, the difference is too slight to be significance, but sometimes not. 

The meridian flip automation i use includes a re-centering of the target via plate solve, which I think is pretty common


Brian


On Sat, Jul 18, 2020 at 8:48 AM uncarollo2 <chris1011@...> via groups.io <chris1011=aol.com@groups.io> wrote:

It seems as though the autoguider commands are being interpreted as user initiated slews.
Yes, autoguider commands are essentially user initiated moves which cause the mount to go to a new coordinate every time a move command is issued. This is universal and applies to every mount ever made, whether AP mount or other brands. They will all do the same.

Rolando


-----Original Message-----
From: Michael Dolenga via groups.io <giroditalia=yahoo.com@groups.io>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Sat, Jul 18, 2020 9:31 am
Subject: [ap-gto] Mount coordinates change while autoguiding

I've noticed that my 900GTO's coordinates, as reported by ASCOM (latest version of the driver) change over a session where I am autoguiding. This occurs whether using MaximDL or NINA/PhD. In both cases, I am configured to send autoguider commands via the ASCOM driver rather than a separate ST4 cable.

This confounds automated meridian flips because the mount "thinks" it is pointed somewhere other than where it actually is. Often, the difference is too slight to be significance, but sometimes not. 

As an example, last night I was doing 30 minute shots of the Crescent Nebula. Over one hour, as reported by the RA/DEC fields written into the FITS header, I saw a difference of 6 minutes, 4 seconds in RA and 1 minute 7 seconds in DEC.

If I leave the mount running with no autoguider connected at all, RA and DEC remain constant, as I would expect.

Is this expected behavior or am I possibly missing some configuration option? It seems as though the autoguider commands are being interpreted as user initiated slews.


Michael


--
Brian 



Brian Valente

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