The Bahtinov mask in astrophotography is very useful as it allows you to understand when the ideal focus for the instrument has been reached.
Bahtinov masks can be used on all instruments without exception, the important thing is to choose it of the right diameter.
The variable measure is to be considered in millimeters for the diameter of the external tube.

How does it work?
Each mask comes with three locking screws, operation is very easy, just place the mask in front of the telescope aperture and point a bright star.
On the computer monitor or on the reflex camera you will see a squashed X with a line in the middle
If the center line at the X is above or below the center, you are in intra or extra focal, so you need to correct the focus.