Focus repeatability issue


Jim Fakatselis
 

I am imaging with a QSI683WS8 and a Starlight Instruments focuser with the Starlight stepper motor on an AP130mm EDF refractor Using MaximDL.

I was attempting to measure the filter offsets with my AstroDon series E gen 2 filter set. Taking four sets of measurements repeatedly with 5 of the 7 filters I use most, L, R,G,B,Ha.  If I try to immediately refocus, my focus setting continues to drift monotonically. Very erratically. Can’t get repeatability at all. 
This past evening four V curve runs on just the Luminance filter in rapid succession, (less than 2-3 min per V curve), over and over produced readings like this:
15020, 15101, 15140, 15213 as an example. 

The other filters behaved similarly.  I can provide Excel plot of data with linear ramp. 

Reported temp from HSM stepper is well within 1 deg, measurements were made about 2-3 min apart in rapid succession. Little to no temp effect should be present.  

Any ideas on what I should look for to determine source of this erratic behavior?
The last few weeks there has not been an issue like this, this seemed to develop suddenly. No change to imaging train, it’s been untouched.   Seeing?

Thanks in advance,
Jim

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