Just reporting back that I successfully set up the filter offsets with my QSIwsg-5 using L for autofocus with my 4" TSAPO100Q. I took my time, maybe a couple of hours to check the offsets several times and once all was done there were only 3 steps difference between the 5 filters HaLRGB, so I’m guessing my Astronomik TypeII filters come out pretty much parfocal, at least when shooting though the 4" - I’d noticed slightly bigger focus differences shooting through the C14. I had other issues to fix last night getting PHD2 to play with the new set up, but I did shoot a single 10 minute Ha sub of IC443 (Jellyfish Nebula) and the new focus ran smoothly .
I did a quick ArcSinH stretch and noise reduction on the single sub, but no calibration (Flats, darks, etc. hence hot pixels & bad columns), just to check what I’d got. Stars look good, but boy this is a faint target, as it was almost invisible without the stretch…
Many thanks for the help, I now feel ready to go capture some proper data next time we get some clear skies.