In addition to focussing, the tri-Bahtinov also indicates collimation status along three axis. You could basically do the same by turning your classic Bahtinov at 120° angles and check focus each time.
I used a lasercutter at the KU Leuven to create the mask based on a vector graph generated with the mask generator: http://svg2.mbsrv.net/astro/Tri-Bahtinov.html
To collimate the SCT, you follow the following generic process:
- collimate for concentric shadows on an out-of-focus star disk
- focus closer and collimate again
- focus almost to focus, look for irregularities and collimate again to have eccentricities to disappear
- when seeing allows you can check the airy rings, and collimate to make those go around the disc
The last 3 steps require very small turns on the collimating screws.
- With the tri-Bahtinov you repeat step 1 and 2 put on the mask and focus till one of the three pairs of beams is in focus
- check by blocking the light of each section (1 out of 3) which line is in focus
- use one of the two other collimation screws to focus (one of) the other beams
- repeat till the image is totally balanced
Check out: https://github.com/cytan299/tribahtinov