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Collimation woes
So I just took ownership of a SW 10" Goto dobsonian. It's a step above my dad's old late 70's 130mm newt Tasco on an eq mount. The clarity difference is mind boggling, although the old scope has done well for it's age.
The tools I was using are a ProStar Laser, and a Farpoint Cheshire. I put everything together and started out on the alignment.
Been trying to get my head around the collimation process, even after much reading on it the scope wasn't adding up.
I initially did it with the laser, doing the secondary and primary was easy enough until I checked it with the chesire and it looked completely out.
So I thought I'll do the opposite and collimate with the cheshire and check with the laser. I thought it looked quite good when I did it with the cheshire, everything lined up. I popped the laser in and nothing lined up according to the laser, way off....
I couldn't understand what was happening. So I attempted to tweak the collimation of the laser, after messing it up for a while I got it to stay stationary when rotating it in the jig I made up for it @ 6m away.
I repeated what I did again, aligned with laser, checked with cheshire. Still didn't check out with the cheshire, The primary spot lined up but the secondary mirror didn't have half the mirror clips in there like it would if I initially collimated with the cheshire. Instead it had a fair portion of the OTA in view.
It didn't make sense...laser was straight...but doesn't marry up with the cheshire. If I collimated with the cheshire, it looked great...till I checked with the laser and the secondary was way off.
So, then I noticed the adjustments grub screws on the base of the focuser. I used the cheshire to visually get good secondary alignment. Then popped the laser in with it's own adapter and adjusted the focuser adjustment screws till the laser dot lined up with the primary mirror centre dot.
Swapped the cheshire back in, adjusted the primary to line up well with cheshire, then tested with the laser. Did some minor primary adjustments, then checked again with the cheshire and presto! Good alignment in both.
What got me was, everything I read on collimation in the manuals and on all the different threads and DIY's on the net did not even mention the focus tube alignment. It took me maybe 3-4 hours all up in my spare time playing with it till I had it figured out.
It didn't occur to me the focuser base would of bee off alignment. From this experience, it has shown me that just "trusting" what the laser says isn't always correct...even if it does shoot straight.
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