How To Make and Use a Bahtinov Mask
The Bahtinov mask is a device used to accurately focus astronomical telescopes. It is named after its inventor Pavel Bahtinov.
The Bahtinov Mask is a variation on the Hartmann Mask which uses three separate grids. The grids are aligned in such a way that they produce three angled diffraction spikes on the focal plane of the instrument for each bright star or planet. As the instrument's focus is changed the central spike appears to move from one side of the star to the other. Optimum focus is achieved when the middle spike is centered on the star and symmetrically positioned between the other two spikes. Small deviations from optimal focus are easily visible.
Creation of a Bahtinov Mask is very similar to that of the Hartmann Mask. You should use the astrojargon Bahtinov template generator to create a template for your telescope. You should print the generated template according to the instructions provided.
How To Make a Bahtinov Mask
Cutout the template grid pattern with a sharp knife and ruler. To cut out the short edges I used an old flat head screwdriver and hammer to punch through the card. A steel ruler and stanley knife made light work of cutting the rest of the slots.
Next, cut out the template neatly, leaving an inch extra around the circumference. Snip all around the circumference towards the center. This will create a series of tabs that will attach the mask to the telescope. Fold each on the tabs inwards.
Place the mask onto the telescope, positioning all the little tabs onto the cardboard strip. Fasten the mask to the strip using sticky tape all around.
You can now decorate the mask if you wish, or just paint it black.