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Thread: 12" diameter Meade Dobsonian - need advice on which eye pieces to purchase ASAP

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    Default Re: 12" diameter Meade Dobsonian - need advice on which eye pieces to purchase ASAP

    Quote Originally Posted by LauraHerdingCats View Post
    the initial collimation was performed using the cheapest collimator I could find on that had good reviews: Astromania next generation laser collimator.

    so, I adjusted the secondary mirror at that time to work with the main mirror. have I already caused a problem by using a cheap collimator? And, should I just use this product as a paper weight/recycle into the trash? Do I need to buy a proper collimator?
    Depends. Cheap laser collimators are just fine if you know how to use them. There are two main issues:

    (1) The collimator itself may need to be collimated. Roll it around and see if the projection on the wall goes up and down (or stick it in the focuser and rotate it, see if it makes a circle on the primary). If yes, find the screws under the goop/stickers and adjust them until this does not happen anymore. Best to make a stand of four long nails crossed to turn it around on. It's a one-time thing.

    (2) The collimator does not fit snug in the focuser. Maybe you can compensate for it manually, or else put some tape around it until it is snug.

    Then you should be able to use it reliably. What I find the hardest step is the squaring of the secondary under the focuser. I usually loosen all screws including the main one and move it in place, then adjust until everything is tight and centered. A sight tube is not a bad idea.

    Sometimes the collimation is so far off that the returning beam misses the secondary. In that case a Cheshire is handy. I like laser collimators best though despite all this because the laser dot is so bright and so sensitive to the mirror position.
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    Default Re: 12" diameter Meade Dobsonian - need advice on which eye pieces to purchase ASAP

    a 12" has some serious light gathering potential, enabling you to see an awful lot of things. I would like you to consider not neutering it by going with lower quality accessories, which includes collimination. Collimination is a critical part of getting max performance out of your scope and "cheaper" devices make this much harder to do. The higher end ones, while also eliminating many of the subtle issues of teh less expensive models, usually are actually easier to use!

    When I purchased my current scope I didn't know the first thing about collimination .... one of the members here who happens to own the same scope, recommended I look into the Hotech laser colliminator system. It's certainly not cheap but I went with it and even teh very first collimination I did after assembling the scope for the first time, instructions in one hand , took less than 5 mins to complete because the device is so well thought out ... just something to consider.

    BTW, since your scope is f/5 you probably also need to be careful about EP choices as at that speed you are starting to be at the point where premium, highly corrected EPs are important.
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