Date   

Re: Adjust CP4 Clock Frequency

Roland Christen
 


So the best I can do is point at DEC 0 and HA -3
It will have to do.

I was of course assuming that your drift rate of 0.1% was using the raw sidereal rate and not a custom rate in APCC or any other model rate. Or are you saying that the drift rate of 0.1% is caused by your APCC model?

Roland Christen


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 6:48 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

By chance we will have a clear night tonight (and near full moon) so I should be able to run the tests.  To make sure, I assume you want APCC to not use the pointing model or any tracking corrections during these tests?  I will do a plate solve at the start and end of each test (5 minutes).  This will give me a precise measurement of the drift rates in both RA and DEC.
The third test is a problem though.  The building the mount is located in does not permit observations below about 45 degrees.  So the best I can do is point at DEC 0 and HA -3 .. is that okay?

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

By chance we will have a clear night tonight (and near full moon) so I should be able to run the tests.  To make sure, I assume you want APCC to not use the pointing model or any tracking corrections during these tests?  I will do a plate solve at the start and end of each test (5 minutes).  This will give me a precise measurement of the drift rates in both RA and DEC.
The third test is a problem though.  The building the mount is located in does not permit observations below about 45 degrees.  So the best I can do is point at DEC 0 and HA -3 .. is that okay?

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 

If you are seeing a 0.1% error in your basic Sidereal tracking rate (assuming that you have polar alignment for min drift pointing straight up) then something is definitely wrong and you should make arrangements to send the RA axis and your controller in so we can check it out.

You can do this test and report the results:
1) point the scope straight up with counterweights in the West. Check the drift rate of a star for 60 seconds, or better yet 5 minutes, in RA.
2) repeat the test with the counterweights in the East.
Note the drift rate as + or -.
3) send the scope to a star toward the eastern horizon and note the drift rate in Dec.

Roland Christen



-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 5:50 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

If the Sidereal rate is 15 arcsec/second then a 60 second image will have a movement of 15 x 60 = 900 arcseconds.  If the error is 0.001 then the drift will be 900 x 0.001 = 0.9 arc seconds which is about 2 pixels on my plate scale.  A 5 minute image will then be 0.9 x 5 = 4.5 arc seconds .. or about 10 pixels .. this is what I am seeing.  But what if the drift is lower than this .. say 0.0001 then the tape measurement must be accurate to 0.05mm.  I think when a mount of this calibre has encoders (at over $6000 cost) and can easily determine pulses per period of time .. why don't we have this?  This is not confidential information, just a simple metric to make sure everything is calibrated properly.  I think using a piece of tape is not the method a mount of this calibre deserves.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

If the Sidereal rate is 15 arcsec/second then a 60 second image will have a movement of 15 x 60 = 900 arcseconds.  If the error is 0.001 then the drift will be 900 x 0.001 = 0.9 arc seconds which is about 2 pixels on my plate scale.  A 5 minute image will then be 0.9 x 5 = 4.5 arc seconds .. or about 10 pixels .. this is what I am seeing.  But what if the drift is lower than this .. say 0.0001 then the tape measurement must be accurate to 0.05mm.  I think when a mount of this calibre has encoders (at over $6000 cost) and can easily determine pulses per period of time .. why don't we have this?  This is not confidential information, just a simple metric to make sure everything is calibrated properly.  I think using a piece of tape is not the method a mount of this calibre deserves.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 

1100 mount diameter is 175mm, yielding an error of more than 1/2 mm (.022inch) which you will definitely see with the tape lined up.


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

I'm not sure the test will be accurate enough.  If the diameter of the circle the tape is on is say 150mm then the circumference is about 471 mm (c = pi * diam).  If the clock error is 0.001 then the error after 24 hours would be 471mm * 0.001 = 0.47mm .. not sure if I can accurately see that.  On the other hand, the number of encoder pulses for a period of time should be known very accurately .. without revealing the confidential information, how about a test in APCC where you set the time and the software reports the number of pulses recorded.  Seems like that is a basic test and could be added to the AE tab to check calibration, tracking rate, etc.  That would be far more accurate than cutting a piece of tape.

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

I'm not sure the test will be accurate enough.  If the diameter of the circle the tape is on is say 150mm then the circumference is about 471 mm (c = pi * diam).  If the clock error is 0.001 then the error after 24 hours would be 471mm * 0.001 = 0.47mm .. not sure if I can accurately see that.  On the other hand, the number of encoder pulses for a period of time should be known very accurately .. without revealing the confidential information, how about a test in APCC where you set the time and the software reports the number of pulses recorded.  Seems like that is a basic test and could be added to the AE tab to check calibration, tracking rate, etc.  That would be far more accurate than cutting a piece of tape.

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 

You are asking for confidential information.
The sidereal drive rate is the same for you when you are doing the drift measurements as well as for APCC when it is doing the sky modeling. Any error present is present for both in the same amount.

Do the test I outlined if you are unsure about the accuracy of the mount's sidereal rate.

Roland



-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 4:44 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

How does the CP4 determine Sidreal Rate when using encoders?  For example, does the CP4 count encoder pulses over a given period of time?  Assuming the pulses represent an arc of the mount and knowing precisely the arc change per given time period it would seem this could be used to check the tracking rate.  Which would then imply a precise calibration of pulses per arc length.  How is that done?

Craig


Re: Adjust CP4 Clock Frequency

Craig Young
 

How does the CP4 determine Sidreal Rate when using encoders?  For example, does the CP4 count encoder pulses over a given period of time?  Assuming the pulses represent an arc of the mount and knowing precisely the arc change per given time period it would seem this could be used to check the tracking rate.  Which would then imply a precise calibration of pulses per arc length.  How is that done?

Craig


Re: Adjust CP4 Clock Frequency

Roland Christen
 


One possibility would be the crystal frequency used for timing.
You are heading down a blind alley on this one. Ray Gralack has been doing some development with APCC that may answer your issue.

If you really want to check your RA driving rate you can set the rate to Stop, place a piece of tape across the stationary and moving part of the RA axis. Cut the tape at the seam between the axis. Get an accurate timer, set it to the sidereal day (23hrs,56min, 4.09sec). Push the timer and set the rate to Sidereal at the same instance and let the axis track until the next day. Check when the tape lines up exactly with the timer. Or you can set it to Solar rate and set the timer to 24 hrs. We have done this a number of times with mounts that people swear are running fast or slow and every time the results are within a small fraction of a second.

Roland Christen
Astro-Physics Inc.


-----Original Message-----
From: Craig Young <craig.young.m8@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 4:23 pm
Subject: [ap-gto] Adjust CP4 Clock Frequency

Rolando mentioned in a recent posting (#70144) the tracking rate is dependent on the controller clock frequency.  Over the years of using my AP1600 with encoders I could never get APCC to provide the same tracking accuracy as other users, even with a 200 point model, so it had to be a problem with this particular mount.  Since this has never be resolved after several hours working with AP I wrote my own tracking program ATRACK which does provide very accurate tracking over several hours.

With ATRACK I know exactly what the RA and DEC tracking rates are because the target drifts no more than 1 or 2 pixels over 4 hours, without the use of an autoguider.  So comparing the 200 point model tracking rate with ATRACK I noticed a consistent error, in both direction and magnitude, which led me to the conclusion there is some base tracking error in the mount that APCC does not correct for.  One possibility would be the crystal frequency used for timing.  This is a known problem in radios which is why they revert to TCXO devices (Temperature Compensated Crystal Oscillators).  Also, on one of my other mounts, there is a setting to adjust the master clock frequency.  I know the basic tracking of the mount is excellent because ATRACK reports no sudden jumps (e.g., cable twists or mirror shift, etc).  And, if there is a clock frequency error then the encoders will provide excellent pointing (which they do) but accurate tracking would not work.  A 200 sample pointing model can provide excellent pointing and tracking but the tracking makes an assumption the sidereal tracking rate of the mount is perfect.  If the sidereal rate is too fast, like on my mount, then the model will not know this and accurate tracking is impossible no matter how big my model sample count or polar alignment.

To test this I ask the guys at Astro-Physics if there is a way to adjust the base clock frequency of the CP4 using APCC.  I made some quick measurements comparing ATRACK rates with APCC rates and found a discrepancy of 0.1% (0.001).  Since APCC is ALWAYS running fast I would then reduce the clock rate by 0.1% and see if it solves the problem.  The adjustment should reduce the tracking rate to match ATRACK.

Craig


Adjust CP4 Clock Frequency

Craig Young
 

Rolando mentioned in a recent posting (#70144) the tracking rate is dependent on the controller clock frequency.  Over the years of using my AP1600 with encoders I could never get APCC to provide the same tracking accuracy as other users, even with a 200 point model, so it had to be a problem with this particular mount.  Since this has never be resolved after several hours working with AP I wrote my own tracking program ATRACK which does provide very accurate tracking over several hours.

With ATRACK I know exactly what the RA and DEC tracking rates are because the target drifts no more than 1 or 2 pixels over 4 hours, without the use of an autoguider.  So comparing the 200 point model tracking rate with ATRACK I noticed a consistent error, in both direction and magnitude, which led me to the conclusion there is some base tracking error in the mount that APCC does not correct for.  One possibility would be the crystal frequency used for timing.  This is a known problem in radios which is why they revert to TCXO devices (Temperature Compensated Crystal Oscillators).  Also, on one of my other mounts, there is a setting to adjust the master clock frequency.  I know the basic tracking of the mount is excellent because ATRACK reports no sudden jumps (e.g., cable twists or mirror shift, etc).  And, if there is a clock frequency error then the encoders will provide excellent pointing (which they do) but accurate tracking would not work.  A 200 sample pointing model can provide excellent pointing and tracking but the tracking makes an assumption the sidereal tracking rate of the mount is perfect.  If the sidereal rate is too fast, like on my mount, then the model will not know this and accurate tracking is impossible no matter how big my model sample count or polar alignment.

To test this I ask the guys at Astro-Physics if there is a way to adjust the base clock frequency of the CP4 using APCC.  I made some quick measurements comparing ATRACK rates with APCC rates and found a discrepancy of 0.1% (0.001).  Since APCC is ALWAYS running fast I would then reduce the clock rate by 0.1% and see if it solves the problem.  The adjustment should reduce the tracking rate to match ATRACK.

Craig


Re: Just for fun with AP1200GTO

Geert
 

You can't imagine in how many ways my name was already written, especially my surname ;-)

Geert

Op di 5 mei 2020 om 17:23 schreef Thomas Fischer <manusfisch@...>:

Sorry GERRT, darn autocorrect!

On Tue, May 5, 2020 at 10:55 Geert <geert.vandenbulcke@...> wrote:

Hello,

 

On 2 May 2020, over a period of 4 hours I took 120 images, each 60s exposure and 60s interval with a 150mm refractor at 1093mm focal length, unguided with my AP1200GTO mount, periodic error correction enabled.  So the mount was just running without autoguider inputs during this period.  This was to measure the changing brightness of a HADS variable star GSC3810-1553. 

 

As I had all those images anyway, I wanted to see how much the mount drifted in this 4 hour period, so I stacked the first and last images and measured a drift in RA of 14.08 arcseconds in RA (3.52"/h) and 66.56 arcseconds in Dec (16.64"/h).  This star is at +55° declination.

 

I suppose a mount with optical encoders would probably do better, but for me this is largely well enough.

 

The image stack can be seen on https://astrob.in/pve8nm/0/

 

Best regards from Belgium,

 

Geert Vandenbulcke


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Re: need learning aids for astrophoto

Don Anderson
 

Hello Dick
Yes there are a lot of things to consider when getting into (or back into) this hobby. however it can be quite rewarding and mentally stimulating.

When you set your equipment priorities, the mount is the most important, just like the foundation of your house!. Get a good mount. Everything else is secondary. For the scope, you want a reasonably good scope with a solid well made focuser that can carry the weight of you imaging train without sagging or flopping around. If you go with a refractor, try to get an Apochromatic (APO) model. There are lots of well made APOs in the 100mm aperture range on the market for a reasonable price. For cameras, the choices have never been wider. If you choose to go with a dedicated astro camera, there are some great reasonably priced CCD cameras out there. The newer CMOS dedicated cooled cameras are relatively inexpensive, some are less than a good new DSLR and a lot lighter as well. If you go that route, don't try to get one with a really large sensor. Large sensor cameras require a scope with a large image circle and these are really expensive.
Take your time and do your research. There are several astro related blog sites like this one out there where you can get good information and lots of opinions!

Remember to start small and work up.

Just some more food for thought! 

Don Anderson


On Tuesday, May 5, 2020, 09:41:46 a.m. MDT, fastqx . <fastqx@...> wrote:


thanks, all of you who responded to my plea.     yep, i'm overwhelmed.    not just by the tsunami of new issues to think about, but also by everyone's kindness and generosity.       one day i hope to be less overwhelmed, but i'll always be grateful.

dick fast
atlin bc

On Tue, May 5, 2020 at 8:33 AM Geof Lewis <geoflewis@...> wrote:
Don,
Thanks for pointing out my error, I should have read the original post. Yes, a 12" will make the difficulties that I experienced with my 10" Meade all the more challenging, but I believe that it is still possible, just probably not from where you'd want to start...
Regards, Geof


Re: need learning aids for astrophoto

Don Anderson
 

No worries Geof! Another challenge Dick is facing is his location. Atlin is in the NW corner of British Columbia near the border with Alaska pan handle. This is on the lee side of the coastal mountain range. Seeing conditions will be a challenge for long focal length astrophotography. We here in Calgary Alberta face the same problem being on the East side of the Rockies. That's why I stick with wide field.
Keep safe.

Don Anderson


On Tuesday, May 5, 2020, 09:33:35 a.m. MDT, Geof Lewis <geoflewis@...> wrote:


Don,
Thanks for pointing out my error, I should have read the original post. Yes, a 12" will make the difficulties that I experienced with my 10" Meade all the more challenging, but I believe that it is still possible, just probably not from where you'd want to start...
Regards, Geof


Re: need learning aids for astrophoto

fastqx .
 

thanks, all of you who responded to my plea.     yep, i'm overwhelmed.    not just by the tsunami of new issues to think about, but also by everyone's kindness and generosity.       one day i hope to be less overwhelmed, but i'll always be grateful.

dick fast
atlin bc

On Tue, May 5, 2020 at 8:33 AM Geof Lewis <geoflewis@...> wrote:
Don,
Thanks for pointing out my error, I should have read the original post. Yes, a 12" will make the difficulties that I experienced with my 10" Meade all the more challenging, but I believe that it is still possible, just probably not from where you'd want to start...
Regards, Geof


Re: APCC Tracking Corrections Not Working #APCC

Ray Gralak
 

Hi Jerry,

I seem to have exactly the same issue. I have the latest V2 dirver, APPC version and a CTOCP4 controller. The
Tracking Correction Status in the APCC Pointing Model window never matches what is in the info bar at the
bottom of APCC. Although I had always thought that there was some sort of conversion happening between the
two sets of values and they were not meant to be the same ...
The values in the Tracking rate correction are in units sidereal secs/hour (RA) and arc-sec/hour (Dec). These values do not include and offset rates that may have been sent via the ASCOM driver for tracking an object (comet/asteroid/planet/sun/moon/etc.).

The values in the status bar are in arc-sec/sec for both RA and Dec, and *include* offset rates.

So, the values won't match unless you do a conversion. In my screenshot the values were dramatically different even after the conversion,

-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 Jerry
Sent: Tuesday, May 5, 2020 7:14 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] APCC Tracking Corrections Not Working #APCC

I seem to have exactly the same issue. I have the latest V2 dirver, APPC version and a CTOCP4 controller. The
Tracking Correction Status in the APCC Pointing Model window never matches what is in the info bar at the
bottom of APCC. Although I had always thought that there was some sort of conversion happening between the
two sets of values and they were not meant to be the same ...


Jerry


Re: need learning aids for astrophoto

Geof Lewis
 

Don,
Thanks for pointing out my error, I should have read the original post. Yes, a 12" will make the difficulties that I experienced with my 10" Meade all the more challenging, but I believe that it is still possible, just probably not from where you'd want to start...
Regards, Geof


Re: need learning aids for astrophoto

Don Anderson
 

I looked at his original post. His scope is a 12" Meade.

Don Anderson


On Tuesday, May 5, 2020, 03:22:20 a.m. MDT, Geof Lewis <geoflewis@...> wrote:


Hi Dick,
I tend to agree with most of the advice you've been getting, BUT I want to say that it is not so difficult to get images with a 10" Meade LX200 and a stock DSLR (mine was the Nikon D90) as that is exactly how I started out. Of course the route that I followed is not recommended, but the first thing I did (that is within a few days) after taking early retirement in 2012 was purchased a pre-owned 10" Meade LX200, at which point visual observing, not photography was my main ambition. However, it didn't take long (about 3 months) for me to try attaching my Nikon camera, then a guide scope + guide camera, focal reducer, etc, etc.. For sure the LX200 mount had terrible tracking and PE, so yielded poor shape stars, but I was excited and pretty pleased to get some reasonable DSO images, plus I learnt a lot on the way. For planetary and lunar imaging where accurate tracking is less of an issue the 10" Meade performed extremely well.
All of that said, it is FAR easier to get better results with a smaller refractor, even piggy backed on the Meade and of course I ended up parting with the LX200 in favour of a pre-owned Astro-Physics AP1200 mount, which is an absolute joy to use, but these are rare items to find, certainly in the UK where I'm located.
Good luck and above all have fun.

Geof

From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Cheng-Yang Tan via groups.io <cytan299@...>
Sent: 05 May 2020 01:04
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] need learning aids for astrophoto
 
Hi Dick,
   I'm not sure that an old 10" LX200 OTA is the correct scope to start with for astrophotography. Its focal length is too long for a beginner even with a focal reducer. It also has mirror flop which means guiding should be done with an off-axis guider.
  
   I'd consider a nice f/6 100 mm to 130 mm refractor. AP sells top of the line refractors -- but getting one new will require a long wait.

  IMO, I'd really recommend buying cheaper equipment to see whether you like astrophotography first before sinking in more than $10k to $20k and then discovering you don't really like it.

cytan

On Monday, May 4, 2020, 06:39:19 PM CDT, fastqx . <fastqx@...> wrote:


thanks, charles, for the advice.    i'm a "re"-new watcher, so i appreciate all new comments.

dick fast
atlin

On Mon, May 4, 2020 at 4:34 PM Charles Thompson via groups.io <cthomp97=yahoo.com@groups.io> wrote:
Dick, there is a choice you will have to make up front on cameras. Either one shot color like the ZWO ASI294MC Pro or monochrome with red, green and blue filters like the ASI1600MM. These are the only two I have used personally and they both have pros and cons.  

For the mount, I would go with the 1100GTO.  Mach2 is over a year wait if you get on the list now. I have a 10" truss RC and it's a little bit much for the Mach1 as well as an 11" RASA. I ran these on the Mach1 and it did ok but I could tell they would be better suited to the 1100.  You call also get absolute encoders on the 1100 but I have never felt like I needed to use them. This subject could get controversial. 

Hopefully that helps some.



Thanks,
Charles

Sent from mobile device.


-------- Original message --------
From: Stuart <stuart.j.heggie@...>
Date: 5/4/20 5:37 PM (GMT-06:00)
Subject: Re: [ap-gto] need learning aids for astrophoto

Dick, get ready for the deluge of advice! LOL! This is THE list for getting help with premium gear. 

I'm pretty certain that an AP1100GTO would be more than adequate for the 12" LX200 OTA. You can get on the list for the Mach2 which I think would be awesome but not sure the wait time for those. Karen or Marj will know.

As for cameras ... if you look in this list's archives there was a very recent lively discussion about the move away from ccd to cmos and which cameras people are favouring.

As for books: you can't go wrong with the classics like Terry Dickenson's Backyard Astronomers Guide but newer resources might be more useful when it comes to gear. 

Camera choice will come down to what you want to photograph. You going to go after planets? One camera. Deep sky? A different camera. 


On Mon, 4 May 2020 at 17:30, fastqx . <fastqx@...> wrote:
i'm an old guy who, after 25 years absence, (now at N 59.5 degrees) wants to watch the sky again. can you help me find a book/course/tutorial that would update me on modern amateur astrophotography? i am building a new dome, and have an old meade 12" lx200. electronics are eff-ed, but ota is just fine. i'm looking for a solid equatorial mount and the requisite "go-to" and tracking software.

dick fast
atlin bc canada


--

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


Re: Just for fun with AP1200GTO

DFisch
 

Sorry GERRT, darn autocorrect!

On Tue, May 5, 2020 at 10:55 Geert <geert.vandenbulcke@...> wrote:

Hello,

 

On 2 May 2020, over a period of 4 hours I took 120 images, each 60s exposure and 60s interval with a 150mm refractor at 1093mm focal length, unguided with my AP1200GTO mount, periodic error correction enabled.  So the mount was just running without autoguider inputs during this period.  This was to measure the changing brightness of a HADS variable star GSC3810-1553. 

 

As I had all those images anyway, I wanted to see how much the mount drifted in this 4 hour period, so I stacked the first and last images and measured a drift in RA of 14.08 arcseconds in RA (3.52"/h) and 66.56 arcseconds in Dec (16.64"/h).  This star is at +55° declination.

 

I suppose a mount with optical encoders would probably do better, but for me this is largely well enough.

 

The image stack can be seen on https://astrob.in/pve8nm/0/

 

Best regards from Belgium,

 

Geert Vandenbulcke


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Re: Just for fun with AP1200GTO

DFisch
 

Gerry, this is a very nice and practical experiment that is very illustrative, thank for the analysis, Tom 

On Tue, May 5, 2020 at 10:55 Geert <geert.vandenbulcke@...> wrote:

Hello,

 

On 2 May 2020, over a period of 4 hours I took 120 images, each 60s exposure and 60s interval with a 150mm refractor at 1093mm focal length, unguided with my AP1200GTO mount, periodic error correction enabled.  So the mount was just running without autoguider inputs during this period.  This was to measure the changing brightness of a HADS variable star GSC3810-1553. 

 

As I had all those images anyway, I wanted to see how much the mount drifted in this 4 hour period, so I stacked the first and last images and measured a drift in RA of 14.08 arcseconds in RA (3.52"/h) and 66.56 arcseconds in Dec (16.64"/h).  This star is at +55° declination.

 

I suppose a mount with optical encoders would probably do better, but for me this is largely well enough.

 

The image stack can be seen on https://astrob.in/pve8nm/0/

 

Best regards from Belgium,

 

Geert Vandenbulcke


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Re: Just for fun with AP1200GTO

Roland Christen
 


I suppose a mount with optical encoders would probably do better, but for me this is largely well enough.
Drift rate is not dependent on whether you have encoders. The primary drift rate is dependent first and foremost on your polar alignment. This is especially true of Dec. The RA drift rate will be affected by how close to sidereal the clock motor is running, and that depends on the crystal frequency accuracy inside your CP controller. These usually are accurate to better than 1 second per day.

Encoders provide precise pointing in both axes and moment to moment tracking accuracy that does not vary due to worm and gearbox errors. Since in your case you were not changing the position of the Dec axis or tracking in Dec, then the motor in Dec was stationary and would be stationary the same way with or without encoders.

Rolando


-----Original Message-----
From: Geert <geert.vandenbulcke@...>
To: main@ap-gto.groups.io
Sent: Tue, May 5, 2020 9:55 am
Subject: [ap-gto] Just for fun with AP1200GTO

Hello,
 
On 2 May 2020, over a period of 4 hours I took 120 images, each 60s exposure and 60s interval with a 150mm refractor at 1093mm focal length, unguided with my AP1200GTO mount, periodic error correction enabled.  So the mount was just running without autoguider inputs during this period.  This was to measure the changing brightness of a HADS variable star GSC3810-1553. 
 
As I had all those images anyway, I wanted to see how much the mount drifted in this 4 hour period, so I stacked the first and last images and measured a drift in RA of 14.08 arcseconds in RA (3.52"/h) and 66.56 arcseconds in Dec (16.64"/h).  This star is at +55° declination.
 
I suppose a mount with optical encoders would probably do better, but for me this is largely well enough.
 
The image stack can be seen on https://astrob.in/pve8nm/0/
 
Best regards from Belgium,
 
Geert Vandenbulcke

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