Re: Precise polar alignment of the azimuth axis


Cheng-Yang Tan
 

I agree that there's always flexure. I have moved to OAG for imaging and that's saved a lot of flexure headaches. 

But for PA if the flexure is minimal, i.e. PA error < 1 arc min with the guidescope as measured by SC, at the Park3 and 90 deg position, I would think that it is accurate enough for most imaging sessions.

As usual YMMV

cytan


On Tuesday, December 29, 2020, 07:17:11 PM CST, Ray Gralak <groups3@...> wrote:


> Do the PA routine in SC as usual with the scope starting at Park 3. Adjust Alt and Az to get your PA to good or
> excellent. At this point, your scope should be about 90 deg from Park 3. Then in SC hit the restart button. This
> time, let SC plate solve with the scope at 90 deg from Park 3. Then once SC is done, send the scope back to Park
> 3. And without touching Alt or Az,  note what what SC reports. It should still be good or excellent to show that
> flexure is not a problem.

Because of gravity, there is always flexure.  It's just a matter of how much.

The bigger the instrument the more flexure there will be. "Piggy-backed" guide scopes, even if they are light, can be subject to flexure exerted on the rings by the primary scope.

-Ray Gralak
Author of PEMPro
Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
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 Cheng-Yang Tan via groups.io
> Sent: Tuesday, December 29, 2020 4:11 PM
> To: main@ap-gto.groups.io
> Subject: Re: [ap-gto] Precise polar alignment of the azimuth axis
>
> Actually there is a way to see whether your guide scope is flexing w.r.t. the mount with SharpCap (SC):
>
> Do the PA routine in SC as usual with the scope starting at Park 3. Adjust Alt and Az to get your PA to good or
> excellent. At this point, your scope should be about 90 deg from Park 3. Then in SC hit the restart button. This
> time, let SC plate solve with the scope at 90 deg from Park 3. Then once SC is done, send the scope back to Park
> 3. And without touching Alt or Az,  note what what SC reports. It should still be good or excellent to show that
> flexure is not a problem.
>
> The above routine is described in SC doc:
>
> Polar Alignment Troubleshooting – SharpCap – Lunar, Planetary, Solar and Deep Sky Imaging. EAA and Live
> Stacking. <https://www.sharpcap.co.uk/sharpcap/features/polar-alignment/polar-alignment-troubleshooting>
>
>
> <https://www.sharpcap.co.uk/sharpcap/features/polar-alignment/polar-alignment-troubleshooting>
>
> Polar Alignment Troubleshooting – SharpCap – Lunar, Planetary, Solar and...
>
>
>
>
>
> I use it all the time to make sure that nothing has moved during PA.
>
> IMO, using the guide scope gives a more accurate PA because of its finer image scale. In my workflow, I do a
> rough PA with PoleMaster (PM) and the PM scope  and then use SC with the guide scope for the final PA.
>
> Also SC tells you what your PA error is while PM just asks you to eye ball the alignment between the dot in the
> square and the circle. I think having a PA error allows you to know how precise your PA is.
>
> cytan
>
> P.S. I've never had any success with drift align with PHD2. I think I'm just not patient enough to wait for drift to get
> the error to a steady value.
>
>
>
> On Tuesday, December 29, 2020, 04:27:13 PM CST, Ray Gralak <groups3@...> wrote:
>
>
> > Try the Sharpcap polar align app using the Polemaster camera.
> > That works for me and allows setups using Sharpcap without a guide camera.
>
> Using the Polemaster camera is the best way to do it.
>
> If a guide camera is used and the entire scope is rotated, there is going to be flexure somewhere, which can affect
> the calculated polar alignment position.
>
> There is only so much accuracy you are going to get with this method with a guide scope.
>
> -Ray Gralak
> Author of PEMPro
> Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro
> 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 Greg McCall
> > Sent: Tuesday, December 29, 2020 1:53 PM
> > To: main@ap-gto.groups.io
> > Subject: Re: [ap-gto] Precise polar alignment of the azimuth axis
> >
> > Hi,
> > Re Sharpcap and Polesmaster.
> > Try the Sharpcap polar align app using the Polemaster camera.
> > That works for me and allows setups using Sharpcap without a guide camera.
> >
> > Greg
> >
>
>
>
>
>
>
>





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