Hola Dick,

Thank you for your detailed answer ! I'm clear now
I thought I was missing something because of this focus reference not ok at start sometimes (we have 2 series of parafocal filters).
I had also this idea to take an image at the end, but I'm not sure how to do a dummy image to move the filter. Looks like a dark would not do it. Can we take an image without giving a target to ACP (telescope disabled) ?

Anyway Bob will fix that for us thank you Bob !

Cheers and thank you again,
PS : one more night on asteroid Scheila in ourtbust which for your info is not a comet (no gas detected with TRAPPIST). Again a collision in the main belt ... ?