Thanks Phil and Profiler,
That is where these forums shine: making experiance accessible!
Based on what you guys have written, and the very good description of my scenario in Profiler's last message, my path forward takes shape:
If I have time I take my 12" dobo and thats it, especially for nebula, GCs, PNs.
If I have not much time and want to look at planets, double starts and other similar objects I should consider a doublet, on my AYO with DSC this would be a nice VA setup.
I see the following options here:
Skywatcher 120mm f 900 ED, that size/ weight is still OK on both my mounts, is not longer and not much heavier than my old Vixen 102M achromat.
Takahashi FC-100D, that is very light, good optics but only 100mm, would be great if they would make a FS-120
A used Star 12ED which is 120mm f 1020 (I know someone selling one)
Question is:
will the Skywatcher or the FC-100 be on par with the 150mm Mak. If taking the central obstruction and difraction effects into account the Mak resembles something like 120-130.
If I get close with any of the above, the faster cooling down and better focuser of a refractor would probably do it for me.
If anyone wonders about the 100mm achromat if have in my signature, this is a kit which was sold 2000 in Germany by BW optics. It's a 3 element Achromat f6 (intended for military Binos) which only works up to 100x and also only because I have 110mm glass path before the focus. Without a glass path anything above 60X looks not good. Great for travel only 400mm long and enough size for some fun on holidays on an alt az mount. This is no planet machine..far away from it.