Manual focus bricked, but autofocus works well


Dear all,

I am facing 2 strange issues with the focuser in SGP:

Issue #1

  • the manual focus key don’t work, nor the goto function
  • but the autofocus works well

the temperature sensor, seems correctly reported

-> what is the difference between auto-focus commands and goto commands at SGP side ? how one can work and not the other ?

disconnecting and reconnecting the focuser in SGP does not help, nor deactivating/reactivating the device in the wiindows hardware management panel

The proprietary focuser software still works fine, even manual commands.

issue #2

  • both the autofucus and the manual focus become locked. once or twice per night
  • disconnect/reconnect the focuser in SGP solve the issue
  • it seems the focuser is still moving and following SGP ordres, but the position feedback seems frozen for any reason.
    might be a communication problem, hardware? software or even both?

Anybody as encoutered such issues? any idea?

the focuser is the USB-FOC.US V3

Latest drivers, latest SGP, win10/64



The USB-Focus driver is not 100% compatible with ASCOM and does not work correctly with SGP.

The problem is the missing multitasking capability. SGP makes intensive use of multitasking and will issue commands without waiting for the focuser to answer the previous command. USB-Focus cannot handle that.

Kind regards,


I had USB-Focus before too and i had lots of problems with it, unfortunately i’m not surprised to see there’s still problems with because their support is terrible.

My first problem was that the motor i ordered didn’t come with any screws at all, also the coupling that came with it had a too large diameter so it didn’t work.
I mailed several times about getting parts and screws that fit, and i was promised to get them several times, nothing ever arrived.
I also contacted the seller, they also got the same promise as me and never got anything.

I ended up sourcing the parts to use it myself, but never got it running stable, disconnects and it suddenly reported the wrong step value (missing a number) so autofocus made it go to the totally wrong position.

My suggestion is that you buy a different motor focus.


Thank you Horia and Xplode for your answers.

We are a team and have 3 of these focuser motor/drivers installed in remote observatories

@Horia, this is what we were afraid of…pretty clear now
we anticipated a little bit and have started to make a new controler and ascom driver by ourselves. Fortunatelly we have a real maker in our team who can do that.
@Xplode, the mechanical side is fixed now, we we faced an issue on 2 motors : the flexible coupler was sliping, we had to glue it on the focuser shaft. The coupler hole in which the focuser shaft goes is just a little bit too large may be 6mm against 6.35mm or something like that). Now this issue is fixed.
So we may keep the motor installed and upgrade the controler and its ascom driver.

in the meantime, the current usb focus are still running, I am currently autofocusing in Chile, while beein in Paris/France, thanks to SGP, amazing…

We also have a Starizona onto a FT focuser at the same place, which works well.

thank you guys for your fast answer, clear skies


Hi guys,

a fresh update following last night.

-> I may have found something : The backlash compensation feature. It was enabled in both SGP and the Ascom driver which also has the same feature. Enabled at both side, with same values.

Not good, these are 2 completly different functions with no link between them. This is not the same function displayed in 2 different windows. So the focuser will receive concurent orders in a short period of time,

-> I have deactivated the backlash compensation at SGP side, keeping it activated at the ascom driver side, which, I guess, should result in the smalest amount of assynchronous orders coming from SGP, following Horia’s advice above.

I will let you know wheither it is sufficient to solve the issue and get a stable functionning



@olivdeso My experience with SGP and USB_focus v3 is opposite to @Xplode’s one: they work together like a charm. I found only one annoying, yet minor, glitch: the real time position of the focuser is not updated in SGP while the focuser is moving, only when it reaches its intended position. I reported the issue to the manufacturer, but I have to agree with @Xplode about service: you get an answer once in a Blue Moon and a solution once in a Pluto revolution, so yes, I’m still waiting for one.

Regarding backlash compensation, I leave it to SGP (not to the ASCOM driver) and I never had a problem. Activating it both in SGP and in the ASCOM driver is a sure path for disaster. The fact that the autofocus routine moves the focuser always in the same direction (inward, which I assume is your backlash compensation direction) could be at least a partial explanation for your symptoms (if you’re moving inward you’re not triggering backlash compensation and the consequent conflict between ASCOM driver and SGP).