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A Tri-Bahtinov mask for SCT collimation and focusing

astrophotography imaging SCT
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#501 Psittacula

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Posted 21 November 2021 - 12:59 PM

I would like to add what I have attempted about Newtonian collimation using the tri-bahtinov mask.

 

First, I used a laser collimator to align the optical axis. In particular, I aligned the center mark on the primary mirror with the laser point. Then, for optical axis alignment using the tri-bahtinov mask, I basically used only the adjustment screws of the primary mirror. I did not use the adjustment screws of the diagonal mirror.

 

Satoru


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#502 Borodog

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Posted 21 November 2021 - 04:29 PM

Thank you both. I just ordered a pair of tri-Bahtinovs for my C8 and C11. Hopefully I can jerry rig the latter one to use with the 10" Dob.



#503 Borodog

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Posted Today, 03:51 PM

Thank you both. I just ordered a pair of tri-Bahtinovs for my C8 and C11. Hopefully I can jerry rig the latter one to use with the 10" Dob.

I got my masks yesterday. I collimated my C8 with one last night, and I just want to say, holy cow! What a revelation. Took me a few minutes to work out how it worked, but once I did, it was easy as pie. I followed these steps:

 

1) Get on a target star and get to rough focus.

2) Put on the mask, oriented such that the sections are aligned with the collimation screws.

3) Obscure the third of the aperture (more or less, doesn't have to be exact) next to a chosen screw, and observe on screen which axis changed in order to get oriented. Don't touch that screw (unless you run out of play in the others).

4) Focus the axis from number 3.

5) Adjust one of the other 2 screws, observe which of the 2 remaining axes changes, and which way the center line crosses that X.

6) Adjust the axis from 5 until the second axis is also in focus; refocus the first axis and re-center the star as needed.

7) Repeat 6 for the last axis.

8) Stare in wide wonder at the joy you have created.

 

I can't wait to collimate my 1100 EdgeHD tonight!


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