Relative focuser - JMI motofocus using Shoestring's FCUSB

In a previous topic Ken said "I don’t really know anything about this focuser so I can’t speak directly to it. That said…

SGPro will work with any focuser if…
•The focuser reports itself as absolute (even if it is a relative focuser in disguise)
•The focuser is accurate enough to return to the exact same spot as reported during a focus run"

How do I do this? Shoestring’s FCUSB is on the focuser list, but when I tried to connect, I received a message that SGP did not support relative focusers. I don’t know how to make it report itself as an absolute focuser.

However, I don’t mind manually focusing, but would like SGP to output an HFR metric that I could use. Currently, I’m using “frame and focus” in Nebulosity for focus, then switching to SGP. The fine focus metric in Neb is as good or better than a mask and I don’t need to slew to a bright star. The SGP HFR, if available, would be better.



This would likely be an option in the FCUSB ASCOM settings if FCUSB supports it. It looks like POTH may have the ability to mask this as well, but I couldn’t get this to function when using a Relative focuser through the sim…YMMV:


Yup, I had the shoestring guy add that as an option before I broke down and bought a stepper focuser.

Keep in mind you can’t have any slippage for that to work. But, with the new focusing routine, it should do a better job of handling errors.

It looks like the ASCOM driver for FCUSB does not have the absolute switch. I’ve downloaded the latest ASCOM driver from Shoestring and it’s not there. Too bad! How about the second part in letting SGP output a focus HFR metric with focus images to allow focusing without a mask.


This is already implemented. Just turn on image history and then use frame and focus. The HFR will be in the upper left corner.

1 Like

I did see that on the shoestring site, but did not see a switch in the ASCOM driver. Maybe, the next time I get out under clear skies, I will see that it is implemented with no switch.


Great! I did not find it in the documentation, but I did not check out the history. I only looked under focusing.