Date   

Re: Adjust CP4 Clock Frequency

Roland Christen
 

According to our servo engineer:
"The CP internal clock uses a crystal controlled oscillator with accuracy of 25ppm, or 0.0025% One way to test the oscillator is to read time of day, :SL#, and compare to a wall clock or precision time with similar accuracy (not a computer clock), over a period of time".

:SL# can be entered in the terminal mode in APCC or directly using our Ethernet Terminal app.

Roland Christen



-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Wed, May 6, 2020 5:40 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

The graph shows clearly that a small change in servo sidereal rate will result in a significant drift in RA, 10 arcsec over 700 seconds.

Last night ATrack showed an average drift in RA of -0.01500 arcsec/sec.  The drift range for RA on my system is always between -0.01200 and -0.02000 no matter what the temperature or where the scope is pointed.  It says the RA tracking rate is always too fast.  The range is most likely due to refraction, polar mis-alignment and other mechanical deviations.  But the underlying base (e.g., -0.01000) is constant.  Using an average of -0.01500 arcsec/sec means a drift rate of 10.5 arcsec over 700 seconds .. very similar to what you see in the graph above.

Even more important is when I use the APCC model correction it has a different value for the RA correction, BUT it tracks in parallel with ATrack correction.  Meaning, the two corrections are in parallel.  This would indicate a tracking error constant that APCC is not accounting for.  The likely reason is a 0.1% error in the servo sidereal rate.  But I would also agree it could be something else.  If the model is not accounting for actual mechanical changes in the mount then there will be a divergence over time between the APCC model tracking correction and ATrack tracking correction.

One thing I can try, ATrack has the ability to provide a "base" correction to the motors, this is to take into account a constant between the motors and the real time tracking.  On my next clear night I will set the base tracking rate and then turn APCC tracking correction back on.  In effect this will simulate changing the servo sidereal rate which is then modified with the model correction rate.  I should see a much improved tracking anywhere in the sky, depending of course on how accurate the model reflects actual sky conditions.  But it should be better than it is without the base correction.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 


The graph shows clearly that a small change in servo sidereal rate will result in a significant drift in RA, 10 arcsec over 700 seconds.
Yes of course it does because I artificially change that rate by 0.1%. The internal clock we use is accurate to a very high precision. It does not drift to 0.1%. Your assumptions are wrong.

Now, you did not take the data that I asked for, so I cannot make any determination of the accuracy of the mount. Would you care to try again when the sky is clear? Otherwise we are going in circles. When I get the numbers from you, for test 1, 2 and 3, I will ask you to do the next step and another set of tests.

Rolando


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Wed, May 6, 2020 5:40 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

The graph shows clearly that a small change in servo sidereal rate will result in a significant drift in RA, 10 arcsec over 700 seconds.

Last night ATrack showed an average drift in RA of -0.01500 arcsec/sec.  The drift range for RA on my system is always between -0.01200 and -0.02000 no matter what the temperature or where the scope is pointed.  It says the RA tracking rate is always too fast.  The range is most likely due to refraction, polar mis-alignment and other mechanical deviations.  But the underlying base (e.g., -0.01000) is constant.  Using an average of -0.01500 arcsec/sec means a drift rate of 10.5 arcsec over 700 seconds .. very similar to what you see in the graph above.

Even more important is when I use the APCC model correction it has a different value for the RA correction, BUT it tracks in parallel with ATrack correction.  Meaning, the two corrections are in parallel.  This would indicate a tracking error constant that APCC is not accounting for.  The likely reason is a 0.1% error in the servo sidereal rate.  But I would also agree it could be something else.  If the model is not accounting for actual mechanical changes in the mount then there will be a divergence over time between the APCC model tracking correction and ATrack tracking correction.

One thing I can try, ATrack has the ability to provide a "base" correction to the motors, this is to take into account a constant between the motors and the real time tracking.  On my next clear night I will set the base tracking rate and then turn APCC tracking correction back on.  In effect this will simulate changing the servo sidereal rate which is then modified with the model correction rate.  I should see a much improved tracking anywhere in the sky, depending of course on how accurate the model reflects actual sky conditions.  But it should be better than it is without the base correction.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

Hi Christopher,
Take a look at the DONUTS article I posted above, ATrack, a software program I developed, follows closely what they did.  In other words, to maintain the very high tracking accuracy, ATrack does both drift correction AND re-centering.  After three or four images ATrack has corrected the drive rates to achieve tracking errors less than 1 arc-second per 60 second images.  But small errors in drift can add up and move the image away from center.  But re-centering done very carefully after each science frame (see DONUTS article) maintains an absolute centering over several hours, on my system, of about 0.2 arcsec for both RA and DEC.

My location is in New Zealand, and the seeing is about 2.5 arcseconds.  I use Pinpoint to provide very accurate plate solves which gives subpixel accuracy (after I fine tuned the plate solve parameters).  The OTA is a GSO 16" RC, and the optical train behind the mirror is a Moonlite NC and a SBIG 6303 camera and FW.  If this system was poorly designed then I would see some significant random jumps in the plate solves .. I do not.  So the system is very solid and predictable .. which is why ATrack works so well.

For example, last night I did four photometry runs: HA 0 to HA +3, HA -3 to 0, HA 0 to +3, HA -3 to 0.  In all four cases the ATrack drift rate corrections for RA and DEC were pretty much the same, so it didn't matter the DEC or the HA.  And in all four cases the difference from the last frame and the first frame was less than 0.5 arcsec.  This shows the stability of the entire system, including the mount, OTA and instrument optical train at the back of the mirror.  Temperatures went from +10C down to +3C by the end of the night.  And there was a full moon up which really didn't affect the imaging much due to the very small FOV and angular distance from the moon.  There was no significant cloud or fog in the sky to scatter the moon light.  So overall, a very successful night.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

The graph shows clearly that a small change in servo sidereal rate will result in a significant drift in RA, 10 arcsec over 700 seconds.

Last night ATrack showed an average drift in RA of -0.01500 arcsec/sec.  The drift range for RA on my system is always between -0.01200 and -0.02000 no matter what the temperature or where the scope is pointed.  It says the RA tracking rate is always too fast.  The range is most likely due to refraction, polar mis-alignment and other mechanical deviations.  But the underlying base (e.g., -0.01000) is constant.  Using an average of -0.01500 arcsec/sec means a drift rate of 10.5 arcsec over 700 seconds .. very similar to what you see in the graph above.

Even more important is when I use the APCC model correction it has a different value for the RA correction, BUT it tracks in parallel with ATrack correction.  Meaning, the two corrections are in parallel.  This would indicate a tracking error constant that APCC is not accounting for.  The likely reason is a 0.1% error in the servo sidereal rate.  But I would also agree it could be something else.  If the model is not accounting for actual mechanical changes in the mount then there will be a divergence over time between the APCC model tracking correction and ATrack tracking correction.

One thing I can try, ATrack has the ability to provide a "base" correction to the motors, this is to take into account a constant between the motors and the real time tracking.  On my next clear night I will set the base tracking rate and then turn APCC tracking correction back on.  In effect this will simulate changing the servo sidereal rate which is then modified with the model correction rate.  I should see a much improved tracking anywhere in the sky, depending of course on how accurate the model reflects actual sky conditions.  But it should be better than it is without the base correction.

Craig


Re: Adjust CP4 Clock Frequency

Christopher Erickson
 

Craig, where are you observing that seeing allows you to keep a 1 arcsecond accuracy on a single pixel for several hours?

Here on Mauna Kea we frequently get sub-arcsecond seeing but we can't even keep the mighty Kecks to that standard of precision for hours at a time. The seeing, even at the summit of Mauna Kea, just simply doesn't allow it.

I frequently (with my personal AP mounts) do photometric and millisecond GPS-timing measurements of stellar occultations and using nearby stars for photometric calibration of each FITS frame. My AP mounts don't have abs encoders and I don't even bother to autoguide.

What kind of OTA are you using for your measurements? I see lots of gravitational sag in my cheaper APO refractors and compound OTA's. Especially in a 20" RCOS truss OTA that I use. At least the sag is predictable and is directly correlated to the OTA's orientation to gravity.

-Christopher Erickson
Observatory engineer
Waikoloa, HI 96738
www.summitkinetics.com
   


On Wed, May 6, 2020, 11:32 AM Craig Young <craig.young.m8@...> wrote:
The ATrack design is very similar to DONUTS, introduced in 2013: https://www.jstor.org/stable/10.1086/670940?seq=1#metadata_info_tab_contents

For high precision photometry it is very important that the image remain centered on the same pixel over the cadence run of several hours.  Dithering is not used.  Given that there can be random drift corrections during the run, the accumulated error can move the target off a pixel, which is why careful re-centering is required in addition to drift correction.

I will find a more precise method for measuring the actual sidereal tracking rate of the mount instead of using a piece of tape, which is not precise enough to yield the metric needed to correct it.  I still don't see why reporting the pulse count from the encoder is proprietary.  I can see "what you do with the pulses in an algorithm" would be proprietary but I don't see why reporting the pulse count is proprietary.  I will find another way then.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 

Measured tracking rate over 600 seconds time period. Each 100 second segment used a precision lab encoder pulse count to determine the exact rate of axis rotation with respect to time. The result is an arc second error graph spanning 6 x 100 second pulse count segments. In the following 700 seconds I added a 0.1% offset error to the servo's sidereal rate so you can see what the effect is.

When the sidereal rate is chosen to drive the mount, the rate of axis rotation is quite accurate over long time periods, but that does not mean that the telescope optical axis will follow that rotation rate. I can easily get a differential rotation rate between two telescopes on the same mount so that if i guide with one scope, the other scope will not keep a star on center for any period of time. So which scope is following the axis rotation rate? The answer is unknown, because both can be flexing in opposite directions from the mount's axis of rotation. Add to that slight polar misalignment and atmospheric refraction effects and I can get easily errors of 5 arc seconds in a 5 minute tracking run.

If you had done the measurements that I asked for, i could continue with the direction needed to solve this for you. But you choose to keep asking for something that is not possible. If you count the encoder pulses, are you able to use a lab standard for the time interval? Computer timers are not accurate enough for meaningful results. We discovered that long ago when we first started to develop our encoder drives.

Your posts are misleading to other people who watch this user group. They are not accurate to what we actually produce and what our mounts actually do.

Roland Christen





-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Wed, May 6, 2020 4:32 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

The ATrack design is very similar to DONUTS, introduced in 2013: https://www.jstor.org/stable/10.1086/670940?seq=1#metadata_info_tab_contents

For high precision photometry it is very important that the image remain centered on the same pixel over the cadence run of several hours.  Dithering is not used.  Given that there can be random drift corrections during the run, the accumulated error can move the target off a pixel, which is why careful re-centering is required in addition to drift correction.

I will find a more precise method for measuring the actual sidereal tracking rate of the mount instead of using a piece of tape, which is not precise enough to yield the metric needed to correct it.  I still don't see why reporting the pulse count from the encoder is proprietary.  I can see "what you do with the pulses in an algorithm" would be proprietary but I don't see why reporting the pulse count is proprietary.  I will find another way then.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

The ATrack design is very similar to DONUTS, introduced in 2013: https://www.jstor.org/stable/10.1086/670940?seq=1#metadata_info_tab_contents

For high precision photometry it is very important that the image remain centered on the same pixel over the cadence run of several hours.  Dithering is not used.  Given that there can be random drift corrections during the run, the accumulated error can move the target off a pixel, which is why careful re-centering is required in addition to drift correction.

I will find a more precise method for measuring the actual sidereal tracking rate of the mount instead of using a piece of tape, which is not precise enough to yield the metric needed to correct it.  I still don't see why reporting the pulse count from the encoder is proprietary.  I can see "what you do with the pulses in an algorithm" would be proprietary but I don't see why reporting the pulse count is proprietary.  I will find another way then.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 


Craig's posts bring up significant points that are quite relevant and should be considered seriously.
Which points did he bring up that are significant to you.? You realize that tracking to sub-arc sec levels is quite possible and has been possible for many years. In your opinion, what are we missing?

Roland


-----Original Message-----
From: Steven Steven <steven447@...>
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Wed, May 6, 2020 3:53 pm
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@...>
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
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 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
>





Re: Adjust CP4 Clock Frequency

Steven
 

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@...>
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
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 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
>





Re: Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO

Michael Hambrick <mike.hambrick@...>
 

I use an 1100 mount with my Astro-Physics 180 EDT and SBIG STXL16200. The 1100 handles this setup without any problems. Here is a photo:




Best Regards

Michael Hambrick
ARLANXEO
TSR Global Manufacturing Support
PO Box 2000
Orange, TX 77631-2000
Phone: +1 (409) 882-2799
email: mike.hambrick@...


Re: Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO

dvjbaja
 

It's all about the moment arm.  Long tube, weight on each end.  The Mach 2 will support the weight. But it may have the Jello effect because of the long moment arm.  



Sent via the Samsung Galaxy Note9, an AT&T 5G Evolution capable smartphone


-------- Original message --------
From: Shailesh Trivedi <strivedi@...>
Date: 5/6/20 11:44 AM (GMT-08:00)
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO

Hi Stuart,

If I absolutely need the 1600 then that may be an option. Alternately I do have a Paramount MX (legacy) with a 90 lb payload  capacity which may or may not suffice. The TEC 180 spec says 37lbs and 44 inches lenght retracted; so by the time I add the FLI camera + FW it adds another 15lbs and focusing will add another 4-5 inches to the length easily.

That said, I am eagerly awaiting the Mach2 notification since its size/weight/encoders for the price are all quite alluring and is the closest I will get to a portable setup. As we get older, our definition of portable changes. Though for me the TEC 180 FL will be far from portable (to some it is easy).

Shailesh


Re: Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO

Shailesh Trivedi
 

Hi Stuart,

If I absolutely need the 1600 then that may be an option. Alternately I do have a Paramount MX (legacy) with a 90 lb payload  capacity which may or may not suffice. The TEC 180 spec says 37lbs and 44 inches lenght retracted; so by the time I add the FLI camera + FW it adds another 15lbs and focusing will add another 4-5 inches to the length easily.

That said, I am eagerly awaiting the Mach2 notification since its size/weight/encoders for the price are all quite alluring and is the closest I will get to a portable setup. As we get older, our definition of portable changes. Though for me the TEC 180 FL will be far from portable (to some it is easy).

Shailesh


Re: Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO

Stuart <stuart.j.heggie@...>
 

Is the 1600 out of reach financially? That is a big, long scope. So weight isn't the only issue.


On Wed, 6 May 2020 at 14:27, Shailesh Trivedi <strivedi@...> wrote:
Hello All,

I have two AP refractors (130GTX and Stowaway). I am also on the April 2019 list for the Mach2 GTO and on waitlist for a TEC 180FL.

I use either a SBIG ST8300M + FW or Proline FLI 16803 (heavier).

My question: I am quite sure that the Mach2 GTO will not be able to handle a TEC 180 + FLI image train from weight & length standpoint.

For such a load, are we talking AP1200 or will a AP1100 do?

Thanks in advance for your advice.

Shailesh


--

Stuart
http://www.astrofoto.ca/stuartheggie/


Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO

Shailesh Trivedi
 

Hello All,

I have two AP refractors (130GTX and Stowaway). I am also on the April 2019 list for the Mach2 GTO and on waitlist for a TEC 180FL.

I use either a SBIG ST8300M + FW or Proline FLI 16803 (heavier).

My question: I am quite sure that the Mach2 GTO will not be able to handle a TEC 180 + FLI image train from weight & length standpoint.

For such a load, are we talking AP1200 or will a AP1100 do?

Thanks in advance for your advice.

Shailesh


Re: Mach2 User Manual

Karen Christen
 

Hello David,

We have not released the Mach2GTO manual yet because it’s not finalized.  The first Mach2 owners all have a draft copy and are providing us with feedback regarding accuracy, completeness, and usability.  We really appreciate their help!  

Karen Christen

AP

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Masera, David
Sent: Wednesday, May 6, 2020 8:38 AM
To: main@ap-gto.groups.io
Subject: [ap-gto] Mach2 User Manual

 

Hi AP,

I am fortunate to be in the current group to receive a Mach2 GTO mount in the next couple of months.  I was wondering if AP would post the user manual on their website for download.  I am new to the automated mount world and would like to learn as much as I can before the mount arrives.  It will be a steep learning curve so any help will be appreciated.  Thanks for all that your team does and stay safe. 

David Masera


--
Karen Christen
Astro-Physics


Re: Mach2 User Manual

Dean Jacobsen
 

I have been waiting for the public release version as well.

David, I was looking through the APCC Pro software manual this morning.  It does reference the GTOCP5 controller which is unique to the Mach2 so at least you can familiarize yourself with the software manual in the interim.  It document is on the Order and Download page.
--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Mach2 User Manual

Masera, David
 

Hi AP,

I am fortunate to be in the current group to receive a Mach2 GTO mount in the next couple of months.  I was wondering if AP would post the user manual on their website for download.  I am new to the automated mount world and would like to learn as much as I can before the mount arrives.  It will be a steep learning curve so any help will be appreciated.  Thanks for all that your team does and stay safe. 

David Masera


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

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
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 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


Re: Adjust CP4 Clock Frequency

Roland Christen
 


I do agree with you that errors in polar alignment, tube flexure, mirror shift, cables, etc can all contribute to factors that will reduce the effectiveness of using APCC for long duration unguided imaging on larger SCTs.
Right now I want to focus on whether or not the basic tracking rate of the mount is correct or not. You claim that the mount tracking rate is wrong by 0.1%, so that's what I'm trying to clear up. Everything else is peripheral right now.

Roland Christen


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 9:31 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Roland,
I do agree with you that errors in polar alignment, tube flexure, mirror shift, cables, etc can all contribute to factors that will reduce the effectiveness of using APCC for long duration unguided imaging on larger SCTs.  I have seen this also on Parmount mounts where ATrack is used to correct tracking over long periods of time, so it is not just an AP problem.  ATrack doesn't really care if the sidereal tracking rate is wrong or polar alignment or any other problem with the system, it is similar to using an autoguider which also corrects tracking, but in a different way.  So there is no real need to try and diagnose the system when it is not really needed.

It is best to simply accept the limitations of the system, which includes the mount, the optical train, the pier and foundation, sky conditions, etc and just plan to use an autoguider or a program like ATrack.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

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

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