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Centre spotting a primary mirror...

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Hi folks,

I'm hoping someone out there has done this already, but I have a small reflector (Skywatcher Explorer 130/900) which is I think is seriously in need of collimating. Problem is the primary (which is spherical, btw) is not centre spotted. That in itself is not an issue but removing it from the tube just might be. My question is - do the retaining screws have nuts holding them in place on the inside or are they self-tapping? If the former, then how do you refasten the screws, without having to remove the secondary spider to allow one's arm to reach right down to the mirror end just to hold the nuts in place whilst the mirror is secured after spotting/cleaning???

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I'm surprised you have not had a reply before now from someone familiar with this scope.

I can' speak for this particular scope. But all the end caps I have removed from scopes built in the last 10 years or so have had threaded holes.

If this really does have loose nuts, then I would look to tap. Or if the material was too thin use nutserts - fasteners to allow thin sheet to be threaded.

Hope this helps, David.

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