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HI Pete,
If, when looking through the Tak scope, you see the secondary dot off from the center or the tak scope dot, then, depending on how far off the dot is, you can tighten and loosen the opposing secondary spider vein supports to move the secondary mirror lateraly until the center of the secondary mirror and the tak dot line up. (be sure not to udjust the spider veins too much as to unduce a bend in them - but you should not have to do this)
Do this for both the horizontal and verticle spider veins.
If your unsure about the tak scope not being orthogonal to the mechanical axis of the scope, then i would suggest (in fact i would sugest to do this anyway) to lock in the tak scope and rotate the focuser. this is best done with the scope pointing down with the focuser retaining screws loose and just sitting in the back of the scope. in this case, the tak scope centre circle or dot should scribe a concentric circle around the secondary center dot.
the aim of this procedure is to get the optical axis of the scope aligned with the mechanical axis of the scope and focuser asembly (and therefor the primary aswell since the primary is bonded to the backplate and focuser).
Now, depending on how far out the collimation is with the collimation screws, this may be an iterative procedure between adjusting the collimation screws and adjusting the spider veins a little since they both have a similar effect.
I use a laser in the focuser tube, and if the laser is out a little or not mounted properly in the focuser, then rotating the focuser will make a concentric circle around the secondary center dot.
an attached picture shows what your trying to achieve when looking up the focuser on axis. concentric circles with the secondary dot centered (confirmed with the previous steps) and the short spider vein reflections in the light annulus ring lined up with the longer spider vein reflections. From here, fine collimation can be achieved under the stars.
If things are not concentric when looking up the focuser and collimation is done by using a defocused star in the center of the chip, then collimation will be off.
Josh
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