Gso rc 200mm question

[pjphilli]

Hi

When I was cleaning the mirrors of my GSO 200mm RC scope I noticed that the secondary mirror has a black spot marked in its centre. What is the purpose/use of this black spot?

Cheers Peter

[RickS]

It's for collimation. I used a Tak collimating scope with my RC10. You try to get the image of the centre spot on the secondary to sit perfectly in the middle of the image of the ring on the primary.

[pjphilli]

Thanks Rick - I am looking into it. Cheers Peter