As you read from the title after one year owning my C8 I finally had to face one of the worst malfunctioning of this telescope: the mirror shifting.
Last week I had a very good seeing and I decided to mount my setup in order to photograph NGC 891. All seemed to go well until 8.30 pm (I begun 6.30 pm) when I had to stop the sequence of shots: phd lost my star guide that had started to become fainter as the minutes passed. I thought soon it was due to a thin dew film on the corrector plate but I was wrong: I looked at the plate but it was dry. I post this comparison between the frist shot and the last one. I have to notice that I began the shots when the telescope was in temperature balance since one hour even though is possible the effect is due to a thermal shifting. I also focused on a star next to NGC 891 in order to avoid the mirror flip, but it seems the problem was neither there.
Meanwhile shooting, the telescope was gradually moving toward zenith, tracking the object. At the final shot the scope was vertical. Do you think the problem could be due to this change on the telescope's orientation? Maybe the primary mirror that was moving very slowly, has gradually increased pressure on the focus screw as the telescope moved to the zenith...just an hypotesis . How can I correct this problem?
Thank all and clear skies