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Thread: Things that made collimation difficult...

  1. #1
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    Default Things that made collimation difficult...



    Hi all, hope you're doing well and the skies have been clear for you!

    Today, as forecast, the rain is coming down nicely I have breakfast, some coffee, and decide to continue working on my newly acquired Tasco T3. In this case, I'm assuming the "T" stands for Tasco (or Towa) and the "3" is what the diameter of the mirror is in inches. This is interesting, as I've found the Tasco model numbers to usually make no sense in relation to the scope. I have a Tasco 11TE-5, which is a 4.5" reflector, a Tasco 12TE that is a 60mm refractor, and two Tasco 55VTE's that are 60mm 'fracs that used to have variable-power click-stop focusers. Well, I guess there is a first for everything...

    The T3 came on the usual "Super Wobble" mount, with a nicely-working .965 focuser, a primary and secondary mirror that needed cleaning, and just generally wanting a good home, much like a stray animal. I'm such a sucker for furry four-leggers and old scopes....






    So clean the mirrors I did (cotton, dish soap and distilled water for rinsing), and purchased a new open box Orion 1.25 focuser. Scope was $40, focuser was $25... You're wondering why for an old Tasco 3". Well, if it puts up images like my 4.5", I consider it money well spent.

    I drill three new holes into the focuser, as they obviously don't line up with the holes on the tube. I also had to make the hole in the scope tube for the focuser tube to go through slightly bigger. I did this with some left-angle tin snips; about a 1/16th" all around. I bolted the focuser on the tube, no binding, so that was good






    I center dotted the primary, using paper the size of the mirror and folded into four, and a cut at the center point, which enabled me to draw a ring on the mirror with a sharpie.
    I then put in the secondary and primary mirrors, and set about to collimating it. Or at least I tried. I used a Cheshire, and while getting the little secondary to line up was no problem, for the life of me the primary was not happening. Wow, all I can get it to do is be centered on the secondary, and no matter what I do to adjust the primary, I can always see the inside of the tube on one side, opposite to the seam.

    That should have been my first clue that it was the scope, not anything I was doing. I don't claim to be an expert, but I've been keeping my dobs lined up optically with a Cheshire for 20+ years now with various scopes, so I tend to think I know what I'm doing. My Tasco 4.5"; I took it completely apart, changed the focuser, put it back together, and had it perfectly collimated in ten minutes. I've been at this for over an hour now....

    I check the focuser, all is tight. I take the primary mirror off again, and check the seating of it. No problem; the tabs are tight and it still "floats" on its foam backing with enough to seat it well. I then take the ring that holds the mirror assembly off, and look to see if there's any casting bumps or the like that prevents it from seating flat. Nope, nary a thing.

    Then I look at the tube.





    Well, no wonder I was seeing the opposite side all the time I took the scope apart again, and then I wrapped some painters tape around the end of the tube, keeping it flat and lined up with the proper edge. Then I took a mild file, and spent a few minutes smoothing it out. I did this with the back part of the tube facing down, and gave the inside a clean with a damp cloth after, just in case.

    I put it all back together again (!!) and hoped for the best. I glanced at the clock, just as it went to 10:47AM. The secondary was no problem, and I had the primary lined up and the whole scope perfectly collimated by 11:02

    So all that to say, if you're "following the manual" and it's not working, it could be a manufacturer defect. Not that those ever happen...

    And that's my words of wisdom for this year Hope you have clear skies!


    All the best,

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    Mark
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    1961 Tasco 12TE 60mm, Tasco 11TE-5 4.5", Tasco 3T 3". And a Canon T3 (1100D)

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  2. #2
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    Default Re: Things that made collimation difficult...

    Holy cow! Makes me wonder how many scopes were relegated to garage or closet duty because they would not collimate.

    Good catch, Mark, and good fix!
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    Bryan
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    Default Re: Things that made collimation difficult...

    Nice acquisition Mark! Now you have both the 4.5" and 3" Tasco Newts - I'm still waiting for the 4.5".

    Hope the optics on it are as good as your 4.5". I still need to take out my 3T out for a proper first light.

    I have an Astromaster 76EQ - same specs as the 3T. The first object I looked at was Jupiter with the supplied 10mm Kellner. Knocked my socks off - really sharp and crisp. Hope it's the same with the Tasco - using the Meade 0.965" Kellner EPs that I have.
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    Default Re: Things that made collimation difficult...

    My first (and only) newt was like that. It would simply refuse to collimate. Put me off reflectors for really long time.
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    Default Re: Things that made collimation difficult...

    It can be frustrating until a person remembers to check the tube. Good catch and fix Mark
    I have had a couple of refractor tubes that were the same.
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