What is a Bahtinov Mask?
A Bahtinov mask is a simple yet highly effective tool for achieving precise focus in astrophotography.
To use it, first place the mask over the front of your telescope’s objective lens or aperture. Then, point your telescope at a bright star and begin adjusting the focus while observing the diffraction pattern it creates. The mask produces a unique set of three diffraction spikes: two remain fixed, while the central spike shifts as you adjust focus. Your goal is to align the central spike perfectly between the two outer spikes, indicating perfect focus.
In this image, in the top frame, the horizontal spike is lower than the center. In the bottom frame, the horizontal spike is higher than the center. It may be subtle, but you can see it if you look closely. In the center frame, the three spikes meet perfectly in the center. That is your goal.
Once the diffraction pattern is symmetrical and the central spike is centered, your telescope is in optimal focus for astrophotography. Carefully remove the Bahtinov mask without disturbing the focus, and you’re ready to capture crystal-clear images of the night sky. This method is significantly more accurate than relying on manual or autofocus techniques alone, making it an essential tool for both beginners and experienced astrophotographers. Whether you’re imaging deep-sky objects or planets, a Bahtinov mask ensures sharp, well-defined details in your celestial photos.