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Equipment Discussions >> Cats & Casses

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Mitchell Duke
Post Laureate
*****

Reged: 04/22/08

Loc: Georgia
Re: Secondary centering expert help needed new [Re: Eddgie]
      #5519881 - 11/14/12 06:03 PM

Ok I ran some test tonight with the scope disassembled, but my collimator crapped out. Instead I tried shinning a led flash light into the back eyepiece holder and I could see a slight misalignment on the poster board. The light on this side was very dim compared to the rest of the light, and as Ed stated I would see part of the image cut off. I then moved the corrector to one side and it eliminated it. I then took a look through the eyepiece holder and the secondary seemed centered. I hope this fixes the problem with the scope. All I know is before I installed the cooling system I never had four lobes on the airy disk on a high powered in focus star. If this does not work im going to forget the collimator and get the Hotech advanced to further isolate the problem. Just got to finish getting Christmas for the family first

Thanks,
Mitchell


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Mitchell Duke
Post Laureate
*****

Reged: 04/22/08

Loc: Georgia
Re: Secondary centering expert help needed new [Re: Mitchell Duke]
      #5519885 - 11/14/12 06:05 PM Attachment (21 downloads)

Just so that everyone understands this is the image of what im trying to fix.

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Dan McConaughy
sage


Reged: 11/11/06

Loc: LA
Re: Secondary centering expert help needed new [Re: Mitchell Duke]
      #5525714 - 11/18/12 08:57 AM

Eddgie,

If you get the time, perhaps you could augment your basic collimation writeup with these other, troubleshooting/mechanical adjusting, steps so that we have a comprehensive reference.

The above was very interesting. I don't think I have a problem with my scope, but I will run through the tests and procedures to verify secondary and baffle tube alignment.

Dan McConaughy


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RussD
member


Reged: 04/20/06

Loc: Minnesota
Re: Secondary centering expert help needed new [Re: Mitchell Duke]
      #5525858 - 11/18/12 10:55 AM

Did you by chance tighten the primary mirror retaining ring? It should only be touching the primary and not really tightened. Otherwise you can induce astigmatism in the primary.

Russ


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Geo.
Carpal Tunnel
*****

Reged: 10/01/08

Loc: Upstate NY
Re: Secondary centering expert help needed new [Re: RussD]
      #5529847 - 11/20/12 11:09 AM Attachment (9 downloads)

Recently picked up a Hotech SCA laser collimator on CN. It would seem to be a great tool for centering the secondary. They advise collimating your SCT and then using the SCA to see if it has changed the next time you collimate. To do this you need to calibrate the amount of secondary misalignment from on center. Here's part of their instructions:

"Commercially made SCTs all have slight optical and mechanical alignment errors. The error typically is in the centering of the secondary mirror. As the result, when a laser is installed and emitted from the focuser, the beam will seldom return dead center, even though star testing would indicate perfect collimation. By default, the laser will have to be position in the optical center of the SCT. Also, the convex secondary mirror expands the fine laser dot to a larger spot, and magnifies any axial error by about 5 times. The error of deviation for a typical well collimated SCT will return laser beam at around 0.125" to 0.250" off center. In order to compensate the optical and mechanical alignment errors of SCT, a different collimation approach is required in compare with Newtonain telescope. If the procedure is followed through correctly, users can still accurately collimate their SCT."

If you apply this process and your secondary returns beam at greater than 0.125" to 0.250" off center it needs to be centered. The SCA collimator can assist you in making those correctors.

You should get a return that looks something like this:


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Mitchell Duke
Post Laureate
*****

Reged: 04/22/08

Loc: Georgia
Re: Secondary centering expert help needed new [Re: Geo.]
      #5530590 - 11/20/12 04:36 PM

I might have it worked out, but i need some good seeing for a star test to make sure. I will keep you informed...

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Ed Holland
Pooh-Bah


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Secondary centering expert help needed new [Re: Mitchell Duke]
      #5530971 - 11/20/12 08:22 PM

Good luck - we're all hoping for you

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