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Starliner Cassegrain/newtonian question

Started by lthaxton, 08/11/2002 02:00PM
Posted 08/11/2002 02:00PM Opening Post
I need a bit of advice/help wit a 12" Starliner cass/newt I recently picked up. Perhaps someone out there can give me a few tips-or better yet, a copy of a Starliner manual. My initial problem is how do you set up and collimate it in the cassegrain configuration? It has adjustments at both the primary and secondary locations. I assume I start at the secondary as in a newt but have no idea how to determine when it is "spot-on." Is this laser territory? Sight tube? Cheshire eyepiece? Any help you can provide would be greatly appreciated!

Thanks!

Larry

(I will post the same message on the scope building board)
Posted 08/12/2002 11:19AM #1
I've never collimated one before so this is just a wild idea. Measure the secondary mirror relative to the front tube opening to ensure that it is exactly centered. Then using the circular opening of the end of your Cheshire as a reference, line up your focuser to center on the outline of the secondary mirror. You can make this adjustment by shimming the focuser's base like with a Newtonian. Then line up the reflection of your Cheshire's crosshairs back onto themselves with the secondary mirror's adjustment screws. Get it PERFECT. Then focus the scope on a star (real or artificial) and adjust the primary mirror to center the airy disc into the comatic flare that you will see if it is miscollimated.

That is how my experimenting mind would explore the situation. But I have never collimated one before so I can't say that it will work, just that I *think* that it will. Eliminate what you can align through conventional means and then do the rest with star images (like when collimating an SCT at 500x on Vega).