Backlash compensation issue with Optec Handy Stepper focuser


I used SGP for the first time last Saturday night. I bought SGP mainly for autofocusing for now. I have a Starlight Instruments/Optec Handy Stepper Motor and Focus Boss II Hub. It connects fine with SGP. I am able to successfully run the “Sequence” including autofocusing.

If I enable backlash compensation (inward or outward), then I use Focus Control to move 1000 steps either direction, the motor moves and then stops communicating with SGP. I have to disconnect and then connect by clicking on disconnect/connect button for this focuser in SGP in order to resume communication. If I then disable backlash compensation, then it works fine.

If I use Optec’s software/driver to set backlash compensation and disable backlash compensation in SGP, it works fine but I am not sure if the actual backlash compensation actually happened.

I found the SGP log showing a bunch of error messages relating to this issue.

I have no other issues so far. Like I said earlier autofocusing works very well as long as SGP’s backlash compensation is disabled. I have sent an e-mail to Jeff Dickerman of Optec about this. I don’t think I’ll hear from him till Tuesday.

Thank you,

I want to clarify one thing. Optec’s software/driver (FocusLynx) backlash compensation does work while SGP’s backlash compensation is disabled.



Anyone see my SGP log files I uploaded. Is it the focuser driver or SGP bug regarding to backlash compensation? I see error messages related to focuser when backlash compensation is enabled (focuser driver backlash compensation disabled).

I am asking why focuser lock up when SGP’s backlash compensation is enabled (focuser driver backlash compensation is disabled). After one command sent by SGP to move the motor, I could no longer control the focuser from SGP’s focus control box. I have to disconnect then re-connect focuser via SGP’s connect/disconnect button.

Everything is fine if SGP’s backlash compensation is disabled with focuser’s driver backlash compensation enabled.


No response, huh?

Well, I guess I will have to keep SGP’s backlash compensation disabled and and leave my Optec focuser’s software/driver backlash compensation enabled. This setup seems to work fine but it would be nice to know if this is a bug in SGP or focuser’s software/driver.


Not sure. There may be something off with backlash comp. We will try to
look into this when we have time.

We found an issue in SGP. We’re addressing it now.


Jared Wellman
Co-Owner and Developer
Main Sequence Software

Thank you very much.


I just downloaded and installed latest 2.3.13 and it fixed my issue. I am not sure why I didn’t try this version earlier.

With focuser’s driver backlash compensation disabled and SGP’s backlash compensation enabled, I finally can send focuser’s new position to the focuser without SGP focuser’s locking up or stop communicating with the focuser. I can physically see the motor overshoot and then reverse direction to the proper focuser’s position. It never happened in previous two revisions.

Next test will be auto focus run. Hopefully the weather will clear up this weekend.

Thanks for fixing this.


Hello, would you please explain me how to measure the backlash on the optec focuser
(i 'have the same setup as yours)

Thanks a lot.



For my focusers, I rigged up a means to place a dial gauge so that it would read the focuser position. I then moved the focuser in both directions, recorder position and step info and crunched some numbers. From this, I found that my Optec TCF focuser has 42 steps of backlash and is quite consistent. This is only used to measure the focus position when the scope is “on the bench” and not set up for observing.

The way the backlash is implemented though, you don’t need a real accurate number as when focusing with backlash comp it will add your backlash to the desired position to move past it, then move back the backlash amount. This only happens when focusing in the direction you select as in or out for backlash comp. As long as your backlash comp setting is more than what is measured, then you should be fine (within reason). For my Optec, I use 75 steps and have no focusing issues.

One sign I see with my setup of not having backlash comp set up properly is when using autofocus, the HFR of the second point on the right is higher than the rightmost point. If you get a nice V or U curve, the backlash comp is OK and is not a driver for focusing issues.

Frank Z…

No need to measure. I just set to 99 steps and let it overshoot and then it will be well compensated. SGP’s manual also said to overshoot.


All right, thanks guys