Tri-Bahtinov Mask

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:

To collimate the SCT, you follow the following generic process:

  1. collimate for concentric shadows on an out-of-focus star disk
  2. focus closer and collimate again
  3. focus almost to focus, look for irregularities and collimate again to have eccentricities to disappear
  4. 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:




Leave a Reply

Your email address will not be published. Required fields are marked *