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Collimating a F/4 AT reflector

Started by De Lorme, 06/30/2012 09:43PM
Posted 06/30/2012 09:43PM Opening Post
Hi, I need some help in collimating my 10" AT f/3.9 reflector. I centered the secondry under the focuser. Next I used the 3 outer screws to center the primary tabs into the secondary mirror. Last I centered the Primary using the primary ajusting nobs to the secomndary mirror. When I put the cross hair chelshire into the focuser the cross hairs do not line up with centered primary. I can center the secondary to the cross hair and than center the primary to the cross hair but when I do there's ony 2 tabs in the field of view. Am I getting the full use of the mirror when I do it this way. Is it better to just center the 3 tabs and then center the primary{with it's ajusting nob's}, and then do a star test? Thanks for your advice. De Lorme
Posted 07/01/2012 04:04PM #1
Read this article and see if this technique helps your collimation:

http://www.astromart.com/articles/article.asp?article_id=827
Posted 07/13/2012 10:07PM #2
James,

Maybe someone else can confirm or deny this, but I think what you are seeing with the cross hairs could be the offset of the secondary via the spider. Is it the X of the spider in the OTA that is not lining up perfectly centered with the X of the Cheshire. If everything else appears to be centering up right but the spider X this would be my guess, having to tip the secondary up so far it throws the primary reflection high enough to cause the mirror "clamps" to disappear from the bottom of the picture tends to confirm my suspicion of this.

If it is in fact the offset showing, collimate it as normal & just ignore the spider X not lining up perfectly with the Chesire X.

Mark J.