Auto Focus, Rigel nSTEP and QHY367C


Thanks for the suggestion Barry. I will add that to my tweaking list for the next clear night. I’ve gone ahead with your setting position suggestion for backlash compensation. Fingers crossed.



Thanks Kinch. Really appreciate the help.



Did some fine tuning last night. Ended up with the Rigel focuser backlash set to IN @ 55. Started at 35 as Barry suggested. All the other settings I left as before.

Here are two screen shots. The first is with the Backlash @ 55, the second @ 61.

Not that I’m picky, which I am, any ideas on how to improve the V-curve? Not quite there for that sharp V shape.

3 Auto 05092018 3601.JPG

7 Auto 05092018 3567.JPG

Seeing wasn’t perfect last night, and I had periods where gossamer clouds drifted overhead.

Tried Plate Solving, Center Here for the first time. Worked. Yes!



Well that didn’t go well last night. I setup for a full night of imaging, but when I manually focused with the mask then ran the auto focus using the settings I used for the first image of my last post just above it wasn’t even close. I tried for two hours to find the settings that would work and didn’t even come close to repeating the graph.

Got a so-so graph, but in five hours worth of imaging, I really didn’t get many usable frames. I had the auto focus set to run every two degree C drop, but it doesn’t look like that happened. It appears to me that after auto focus the images gradually came into focus as the OAT and scope dropped. But then the auto focus would run and be out of focus again.

Any ideas as to what might cause this to happen? And why the settings from before didn’t achieve the same results?

Going to try again tonight as CS are forecast.



Hi Bill,

Very strange but Just a thought, do you have power to the focuser controller. I know I lost a few hours of imaging because I forgot to turn the power on to the focuser. Without power to drive the stepping motor it appears everything is running and the count is changing but in fact the motor is not moving. Might be just a dumb question on my part but thought I would bring it up.



Good point Mark. :rofl:

That certainly would be in the realm of possibility. As far as I know there was power. Double checking that the focuser gears were actually moving is not something I did last night. I’ve overlooked some really dumb things so I will double check the connections and add it to my checklist for the future. If it isn’t turning…



Does anyone know, if you are zoomed in on the image, does SGP narrow the FOV for the determining the focus point or does it use the whole FOV as the camera sees it?

Just trying to eliminate possible variables.



Whole FOV. Zoom level and other settings (histogram, etc) have 0 bearing on autofocus.



Thanks Jared. I’m kind of grasping a straws to get the auto focus up and running properly.



You should be able to check the performance of the focuser during the day… Get some tape, put some tape on the focus knob and mark it somehow so you can see it turning. Or place a toothpick or something to give you a pointer. Watch how the focuser goes in and out and if it hits the same points each time as you cycle. You can work on your backlash. By watching it you will see what I mean and this should help you resolve what is going on.


Good ideas. I do have marks on the meshed gears visible at the focus motor and the scope’s focusing knob. So far the marks continue to be perfectly aligned when I’ve rechecked them after use. But, I will go check during the daytime to see if I can see anything with changes in direction in regards to backlash. I will put some reference marks on the actual scope focus drawtube to compare to the focuser gears.