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Tri-Bahtinov Focus and Collimastion Mask for Celestron 11″ RASA – with Hyperstar or Fastar
You can read how to collimate using the Tri-Bahtinov Mask here: https://github.com/cytan299/tribahtinov or hereĀ https://www.cloudynights.com/topic/536410-a-tri-bahtinov-mask-for-sct-collimation-and-focusing/page-16?hl=+tri%20+bahtinov