This is a SCAD generator for Bahtinov masks. Such a mask is used as a focusing help for small telescopes. An example mask looks like this:
The Generator allows one to generate a focusing mask for small aperture telescopes, i.e. as large as your build volume permits.
If a point source is imaged with this mask, i.e. you put the mask in front of your telescope, it will display an interference pattern for bright sources, that allows to focus the telescope correctly.
For example, using such a mask in front of a 400 mm telescope and imaging a red LED from a Raspberry PI, you can see the correct focus position from the patterns generated by the mask:
From left to right (click to enlarge): As you can see, if the focus is before the point source (on the carpet), the interference pattern generated is asymmetric. If the focus position is at the point source, the pattern is symmetric. If the focus is behind the point source (on the lighthouse model), the pattern is again asymmetric. Using the interference pattern you can set the focus correctly to the plane of the source.
Read this section completely: Download the generator by following this link and saving the file.
Open the file in OpenSCAD (seperate download and install).
Go through the document and set the parameters as you see fit. Then render the mask using F6. When you are
satisfied, export the STL and print.