Re: Adjust RA tracking rate

Don W

Hi Yann,

A new mount should track properly.  The Mesu mounts are very good and very popular.  However I don't have one, so my answer is general to you.

Tracking rate depends on both time and tic setting in SiTech.  So first, make sure your PC clock is accurate and the setting in your SiTech Features/Offset Tracking Rates has the Servo Clock Cal set to 0.99995.  Then watch the "Diff between Computer Time and Scope Time.  That value should stay low (±10 ms) and not climb (either positive or negative).  The clock built-in to the controller is very accurate.  Some PC clocks are not very accurate - the "fix" is to resynch the PC clock with a time server regularly.  I use a program called "Master Synch" and have it update my PC every increment (MasterSynch can do it every 15 seconds or set to minutes or hours).  But that needs internet access.

The process in your reference article at Stargazerslounge is a way to reset the tics/rev to get accurate tracking if your clock is OK or adjusted automatically with Master Synch.

With an accurate clock AND any adjustment per the Stargazerslounge article, you should be able to track for minutes with little error.

There is one other caveat:  Checking the tracking rate for accuracy requires checking it over an RA period.  If your mount has periodic error you must check tracking over that entire period.  I don't know what the Mesu period is.  The best way I know to check the periodic error is using PemPro with your camera.  Then Pempro can create a PEC correction to the SiTech tracking to minimize PE.

SiTech has the settings for Offst Tracking Rate which is easy to use.  You measure the amount of tracking error in arc-sec for a period of time (like 10 minutes) and use the SiTech program to calculate the correction.  This is primarily for tracking moving objects like comets or asteroids, not for overall tracking.

So in summary, Check your PC clock, check the Clock Calibration setting, Measure the tracking error for one full period, Run Pempro for multiple periods (Pempro will show you any drift error) and possible use the PemPro PEC curve to adjust your tracking.  Note that using a periodic error correction needs a sensor on the RA drive to set the synchronization with SiTech.

Don W

---In SiTechservo@..., <yann_eric_boyeau@...> wrote :

Hi everybody,

I am a new mesu/sitech user. I had 2 difficult first nights with the mount learning how it works.
Last setup 0.92ge fixed my phd2 dec guiding rate being twice the RA rate. (0.92ge should be advertised on official website...)


Made my first guided subs 0,5” RMS🤩 not bad ! But corrections in RA were all in the same direction...

My polar alignment error is less than 10 ‘’ and my focal length is 630mm.


Testing unguided (but tracking on) 10min  sub, I noticed trailed stars (70” long).


So I read this thread :

I understand this solution but now I have a question :

Is there a better way to adjust RA tracking speed without « cheating » with the number of ticks ?

I read about rate OFFSET in sitech manual, is it the way to adjust RA tracking rate ? How does it works ?

Thanks a lot for your help,


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