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Old 10-02-2008, 12:41 PM
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Starkler (Geoff)
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Join Date: Sep 2004
Location: Melbourne
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Looking at your photo I notice two things.

Firstly, reflection of the primary as seen in the secondary is not centred. I can see one and only one of your primary mirror clips. This suggests that your secondary is out of whack.

Secondly, the centre spot donut appears off centre toward the left of the photo. This might be related to the above.

I strongly advise you put your laser away until this issue is properly sorted as it is only confusing the issue. Assuming your centre spot is indeed in the centre, a long cheshire/sight tube tool is everything you need to collimate your scope and get it right. The same cannot be said of the laser. What type of cheshire do you have? Is it a long one or a shorty one like Andrews sells?

Try seating your cheshire in and rack the focuser in far enough until you can see all of the primary mirror in the secondary. Now adjust the tilt of the secondary to centre it, and then align the cheshire crosshairs over the centre spot. Rotate the cheshire in the focuser 180 degrees and look again. This will check how well centred the crosshairs are in your cheshire tool.
How are we going so far? Can you still see the entire primary mirror fairly well centred in the secondary? If not you maybe have a poorly centred centred spider. I had this issue with my gso dob until i identified and fixed it.

If thats all good, adjust the primary to put the centre spot in close alignment with the illuminated reflective ring of the cheshire.

You should now have a fairly well collimated scope. If the laser doesnt agree to within a few mm, try rotating the laser. As you move it does it trace a big circle around the desired centre? If so your laser is out of collimation and needs adjusting. If it traces a circle way off the desired centre, I would suspect your primary mirror centre spot is misplaced from the physical and optical centre of the primary mirror.

Good luck and let us know how it goes.

Last edited by Starkler; 10-02-2008 at 12:56 PM.
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