I looked into focussing masks a bit and noticed that for Bahtinov masks, everyone seems to use a regular grid. This produces a refraction pattern, i.e. a stripe with rainbows and gaps.
I think focusing should be easier when using multiple overlapping frequencies, which should be much closer to a continuous white line.
In particular, this should be an advantage when using a narrow band filter. I couldn't find anything about this topic, has anybody tried or heard of this before?
I tested a number of configurations with a simulator 'diffractsim'. The attached image shows some results. The ordering seems to have a small influence, I'm not quite sure why. The second mask seems to have the most continuous line, I also attached the corresponding pdf (svg upload is not allowed?).
Unfortunately, I do not own neither the necessary gear for astrophotography nor for fabricating the mask, so I cannot test this myself, but maybe someone here would like to test and give feedback.