If your telescope is larger than your 3D printer, look no further :)
This is a parametric Bahtinov focusing mask split into two or four sections so you can fit your printer. It is based on brentb's original one-piece design.
The Bahtinov mask is a focusing aid for astronomy, and is particularly useful for astrophotograpy. The orignal creator is Pavel Bahtinov. A good description is available here: http://www.nightskyimages.co.uk/bahtinov_mask.htm
The design shown is for a 224mm (8 inch) mask optimized for a focal length of 1000mm. You probably will want to use the Customizer or the OpenScad file to optimize the mask for your particular telescope. A calculator for optimum Bahtinov design factors is available here: http://astrojargon.net/MaskGenerator.aspx
There was a problem with printing the 4th segment when using the customizer which is now fixed. It always worked fine in OpenScad.
Black is the natural colour for this design, to make the blocked sections as dark as possible.
The first layer can be tricky if you build on kapton, since it is very easy for the single lines to become unstuck and mess up the build. I built with 0.4 mm outer walls to reduce the number of single unconnected lines in the initial layer. Also, starting with a really thick first layer may help. I used a layer height of 0.25 and an initial layer heigh of 0.40.
After having built the sections, for stability you will probably want to glue the sections together.