Thank you Adun! I measured now with the measure stick and got down to a reduction of 0,58x which leads to F/D of 3.4. So a little bit better. On the ST80 i can reduce further with some spacers if I do not use the diagonal. However that is not an option on the dob. I'll try how it goes with 3.4. Doesn't sound too bad actually. There is always the option to stack multiple drifts.I assume Ubuntus stacked single drifts.
Hi Sondob... you're right I mostly stack single drifts... but repositioning the scope allows you to stack as many drifts as you want...
F/D 3.4 starts to be good but don´t forget that the objective is to go under 2 (exposition time will be divided by 2.5).
My advice would be to put a spacer to reach this F/D
But I'm already curious to see results with F/D 3.4