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Slewing Scope Needs Collimation - Normal ?

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#1 2020BC

2020BC

    Apollo

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Posted 08 December 2005 - 04:31 AM

I did the following experiment in collimation with my SN-8.

I collimated the scope with a Laser collimator then slewed the scope almost 180d in RA and then I checked it again.

I found that the collimation changes significantly whenever I slew the scope from one side to the other.

Is this normal behaviour? :question:

#2 garyc11

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Posted 08 December 2005 - 09:41 AM

i dont think that is normal. it sounds like the mirror may be loose and moving when you slew the scope. could be something else but i would start by checking the mirror.

#3 matt

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Posted 08 December 2005 - 10:20 AM

Obviously, yes you have something moving in there. You could expect a little flexure or something like that in a large reflector (reason why I usually collimate my dob at 45% angle).

Most newtonish designs have 6 push-pull screws for collimation, three screws which move the mirror back and forth for collimation, and three screws which "press" the mirror to keep it tight. You should tighten those ones. Then check the secondary mirror holder. Repeat.


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