The Tri-Bahtinov Mask is an advanced version of the Bahtinov mask that allows for even more precise adjustments and can also be used as a collimation tool

Tri-Bahtinov Focus and Collimation Mask is an ingenious new way to easily focus a telescope. Pavel Bahtinov, a Russian amateur telescope maker and astronomer, created this simple, very intuitive method and the device has universally been named after him: The Bahtinov Mask.

Tri-Bahtinov Mask is based off the classic Bahtinov mask: it allows to focus a bit more objective compared to visual star focusing.

The Bahtinov will produce Cross-shaped stars, with one clear line that moves along the cross as you focus. When the line is centered on the cross, you should have achieved perfect focus.

 

What is the Tri-Bahtinov?

It essentially three Bahtinov masks in one, rotated over 120 degrees. It gives you three lines and three crosses to check collimation, along three axis simultaneously.

In addition to focusing, the tri-Bahtinov so also indicates collimation status along three axis.

This is interesting for e.g. Schmidt-Cassegrain telescopes, where the collimation is done by push-pull screws of the secondary mirror along three axis.

When you position the tri-Bahtinov alongside these axes, it will give you insight not only per axis of the focus but also how different these focus points are for each axis.

Bahtinov mask is a less expensive method of getting focus on objects in the night sky compared to a standard motor focuser.

With the right mask and setup, it’s easy to get crystal clear focus on a star in less than 90 seconds.

_{Star in focus via a Bahtinov mask}

How it Works

The slits in the mask are the focus assist, when the star is in focus it will appear on your screen display as an “X” with a line through the center (see above).

These mask will work equally as well on the end of a scope or on the end of a dew shield on top of that the mask itself does not need to be perfected centered on the scope this is due to the angle of the slits themselves.

Select a bright star, this will be your guiding object. Place the Bahtinov focusing mask on your telescope’s lens and secure it into place using the provided rubber tabs.

The slits in the mask design create a set of diffraction spikes on the star that will assist in the accuracy of our focus. It will appear on your DSLR display screen or computer as an “X” with a line through the center (when in focus).

The diffraction spike pattern from a bright star using a Bahtinov mask

As you adjust the focuser of your telescope, the central spike will move in and out of the X-pattern. If you are using capture software be sure to compensate for the lag time between exposures on the screen, typically 4-5 seconds.

The same process applies using Live view display on your DSLR camera. The difference is, the image will be much dimmer, as you are essentially looking at a live video feed rather than a short image exposure.

You can read how to collimate using the Tri-Bahtinov Mask here: https://github.com/cytan299/tribahtinov

or here https://www.cloudynights.com/topic/536410-a-tri-bahtinov-mask-for-sct-collimation-and-focusing/page-16?hl=+tri%20+bahtinov

You can read how to collimate using the Tri-Bahtinov Mask here: https://github.com/cytan299/tribahtinov

or here https://www.cloudynights.com/topic/536410-a-tri-bahtinov-mask-for-sct-collimation-and-focusing/page-16?hl=+tri%20+bahtinov