Date   

Re: What are the advantages of the APCC Pro

Michael 'Mikey' Mangieri
 

I actually have the same question. And I have been doing everything just as Steve said. I could have written that email 😎

Also lovin this mount. 

Mikey 


On May 7, 2020, at 2:24 PM, Steve C. Mitchell, Sr., O.D. <smitchell@...> wrote:



Hey Guys,

 

Recently purchased a AP1100 mount and am quite happy with everything so far. Curious about the advantage of upgrading to the Pro version of the APCC software. Been busy modifying my pier so I could mount this beast on it, getting all my equipment set up and running, trying to figure out all the new software…..a plethora of “things to do” lately and been loving every minute of it. Now I’ve got some time to think about this software thing. My initial thought is, you “need” the Pro version if you have the absolute encoders (which I do not have), otherwise it looks to me like an option for a point modeling that should improve the pointing accuracy is the main advantage. Is that correct or is there more to it than that?

 

Steve


What are the advantages of the APCC Pro

Steve C. Mitchell, Sr., O.D.
 

Hey Guys,

 

Recently purchased a AP1100 mount and am quite happy with everything so far. Curious about the advantage of upgrading to the Pro version of the APCC software. Been busy modifying my pier so I could mount this beast on it, getting all my equipment set up and running, trying to figure out all the new software…..a plethora of “things to do” lately and been loving every minute of it. Now I’ve got some time to think about this software thing. My initial thought is, you “need” the Pro version if you have the absolute encoders (which I do not have), otherwise it looks to me like an option for a point modeling that should improve the pointing accuracy is the main advantage. Is that correct or is there more to it than that?

 

Steve


Re: Meridian limits

Ray Gralak
 

We are trying to sort out meridian limits. There seem to be "mount" meridian limits, and "APCC meridian limits".
Have you looked at the help file? If there is something not clear it would be good to know so that we can improve it.

Thanks,

-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 Richard Spencer via groups.io
Sent: Thursday, May 7, 2020 9:07 AM
To: Astro-Physics GTO Users Group
Subject: [ap-gto] Meridian limits

Dear All,

AP 1100 mount, APCC Pro

We are trying to sort out meridian limits. There seem to be "mount" meridian limits, and "APCC meridian limits".

We believe:
--Mount limits apply to slews
--APCC limits apply to tracking and movement into CW up positions

Is that right? Does one set of limits supersede the other? Do we use them together somehow?

Thank you for any guidance!

Rick Spencer
Elkton, MD 21921



Meridian limits

Richard Spencer
 

Dear All,

AP 1100 mount, APCC Pro

We are trying to sort out meridian limits.  There seem to be "mount" meridian limits, and "APCC meridian limits". 

We believe:  
--Mount limits apply to slews
--APCC limits apply to tracking and movement into CW up positions 

Is that right?  Does one set of limits supersede the other?  Do we use them together somehow?

Thank you for any guidance!

Rick Spencer
Elkton, MD  21921



Re: Adjust CP4 Clock Frequency

Craig Young
 

Roland, two tests were requested.  The first one I think was to put tape on the mount to measure the RA drift after 24 hours.  I believe this was done to check the sidereal rate.  Assuming the sidereal rate is calculated correctly using the crystal oscillator then measuring the crystal oscillator will be more accurate than a piece of tape.  So I will do this test first.  If it shows the oscillator is accurate then it does not prove the sidereal rate is off, only the oscillator is good and we can continue from there.

The second test I believe you wanted was to measure the drift with the scope pointed straight up at the meridian and on both sides.  Then a subsequent test at the horizon.  I will do this test at the next clear night but as I mentioned, I cannot observe below HA -3 which I will do but not sure if it helps.  Next clear night is set for Saturday end of this week.

Craig


Re: Adjust CP4 Clock Frequency

Ray Gralak
 

Craig,

You can connect to the mount via a browser and issue commands without APCC or the driver being connected at all.

-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 5:40 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Thanks Roland, that is a big help. So by checking the time we can check the crystal oscillator. And given the
clock is not maintained during the power down state I will run the test with the mount always powered on. So it will
initialize once and then be good after that. I believe there is a setting in the APCC configuration to refresh the CP4
time but I will wait for Ray to comment. Looks like this will be a good test.

Craig


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





Re: Adjust CP4 Clock Frequency

Roland Christen
 

So you simply refuse to do the test I asked you for? Why?

Roland Christen



-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Wed, May 6, 2020 7:39 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

Thanks Roland, that is a big help.  So by checking the time we can check the crystal oscillator.  And given the clock is not maintained during the power down state I will run the test with the mount always powered on.  So it will initialize once and then be good after that.  I believe there is a setting in the APCC configuration to refresh the CP4 time but I will wait for Ray to comment.  Looks like this will be a good test.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

Thanks Roland, that is a big help.  So by checking the time we can check the crystal oscillator.  And given the clock is not maintained during the power down state I will run the test with the mount always powered on.  So it will initialize once and then be good after that.  I believe there is a setting in the APCC configuration to refresh the CP4 time but I will wait for Ray to comment.  Looks like this will be a good test.

Craig


Re: Adjust CP4 Clock Frequency

thefamily90 Phillips
 

🤓☕️🔭🛎


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of uncarollo2 <chris1011@...> via groups.io <chris1011@...>
Sent: Wednesday, May 6, 2020 8:11:19 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency
 

a) does the clock share the same oscillator as used by the electronics responsible for sidereal rate?
b) is the clock on the CP4 updated from APCC and if so how do I disable that, and how frequent or when does APCC update the CP4 time?
c) I assume the clock time is maintained after I power down the mount.  Do I need to keep the mount powered on for the test?
a) There is only one precision oscillator in the CP that does all functions, including setting the sidereal rate.
b) I would have to ask Ray to answer that one
c) the clock time is not maintained when the power is removed. Clock time is set during initialization by the ASCOM driver or by APCC, or by the keypad clock or other external apps, depending on your setup.

The clock inside the CP servo can be updated at any time by external sources, but that has zero effect on the sidereal tracking rate. The sidereal rate is directly set from the precision oscillator.

Roland Christen


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Wed, May 6, 2020 6:50 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

I am not absolutely certain the RA drift is due to an offset in the clock frequency, it is only a possibility among others.  But I do like the idea of measuring the clock using the method you described.  I have a couple of questions though,

a) does the clock share the same oscillator as used by the electronics responsible for sidereal rate?
b) is the clock on the CP4 updated from APCC and if so how do I disable that, and how frequent or when does APCC update the CP4 time?
c) I assume the clock time is maintained after I power down the mount.  Do I need to keep the mount powered on for the test?

I can then use SL# to record the time and then 24 hours later do the same thing.

One thing I noticed a couple of years ago is when I powered up the mount and slewed to a set DEC,HA did a plate solve that each subsequent trial (park, power off, power on, slew) resulted in an increasing error in the position.  It was as if the time base was drifting.  I have not tried this in a while so may schedule that for the next clear night.  But it may be that Ray fixed this in one of the APCC/firmware updates since then.

If the clock does indeed share the same oscillator as the sidereal electronics then this will tell us if the clock frequency is off a bit.

Craig


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

Shailesh Trivedi
 

Thank you Michael.


Re: Adjust CP4 Clock Frequency

Roland Christen
 


a) does the clock share the same oscillator as used by the electronics responsible for sidereal rate?
b) is the clock on the CP4 updated from APCC and if so how do I disable that, and how frequent or when does APCC update the CP4 time?
c) I assume the clock time is maintained after I power down the mount.  Do I need to keep the mount powered on for the test?
a) There is only one precision oscillator in the CP that does all functions, including setting the sidereal rate.
b) I would have to ask Ray to answer that one
c) the clock time is not maintained when the power is removed. Clock time is set during initialization by the ASCOM driver or by APCC, or by the keypad clock or other external apps, depending on your setup.

The clock inside the CP servo can be updated at any time by external sources, but that has zero effect on the sidereal tracking rate. The sidereal rate is directly set from the precision oscillator.

Roland Christen


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Wed, May 6, 2020 6:50 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

I am not absolutely certain the RA drift is due to an offset in the clock frequency, it is only a possibility among others.  But I do like the idea of measuring the clock using the method you described.  I have a couple of questions though,

a) does the clock share the same oscillator as used by the electronics responsible for sidereal rate?
b) is the clock on the CP4 updated from APCC and if so how do I disable that, and how frequent or when does APCC update the CP4 time?
c) I assume the clock time is maintained after I power down the mount.  Do I need to keep the mount powered on for the test?

I can then use SL# to record the time and then 24 hours later do the same thing.

One thing I noticed a couple of years ago is when I powered up the mount and slewed to a set DEC,HA did a plate solve that each subsequent trial (park, power off, power on, slew) resulted in an increasing error in the position.  It was as if the time base was drifting.  I have not tried this in a while so may schedule that for the next clear night.  But it may be that Ray fixed this in one of the APCC/firmware updates since then.

If the clock does indeed share the same oscillator as the sidereal electronics then this will tell us if the clock frequency is off a bit.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

I am not absolutely certain the RA drift is due to an offset in the clock frequency, it is only a possibility among others.  But I do like the idea of measuring the clock using the method you described.  I have a couple of questions though,

a) does the clock share the same oscillator as used by the electronics responsible for sidereal rate?
b) is the clock on the CP4 updated from APCC and if so how do I disable that, and how frequent or when does APCC update the CP4 time?
c) I assume the clock time is maintained after I power down the mount.  Do I need to keep the mount powered on for the test?

I can then use SL# to record the time and then 24 hours later do the same thing.

One thing I noticed a couple of years ago is when I powered up the mount and slewed to a set DEC,HA did a plate solve that each subsequent trial (park, power off, power on, slew) resulted in an increasing error in the position.  It was as if the time base was drifting.  I have not tried this in a while so may schedule that for the next clear night.  But it may be that Ray fixed this in one of the APCC/firmware updates since then.

If the clock does indeed share the same oscillator as the sidereal electronics then this will tell us if the clock frequency is off a bit.

Craig


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

8901 - 8920 of 79099