[Stefan Buda]

This post should really be in the ATM section but the thread I started there, to share my experiments, got promptly locked - probably because I mentioned potential commercial activity.
Anyway, last night I did some testing using various combinations of lenses and masks, with interesting and somewhat surprising results.
Lenses used were my trusty old Pentax 50 f/1.7 and a Mamiya 135 f2.8 attached to a QHY8 camera.
Bahtinov masks with 0.9mm and 2mm slits were tested with both lenses.
Main things learned:
2mm slits work well for 135mm focal length which came as a bit of a surprise.
0.9mm slits produce too much diffraction with the 135mm lens and the patterns are hard to interpret, also a surprize.
2mm slits are not quite good enough down at 50mm, as expected.
0.9mm slits work very well with the 50mm lens.
One needs to choose bright stars for the diffraction pattern to overcome light polluted sky background.

It will take me a while but eventually when I've done all the cutting, pasting and labeling required, I will post the images from last night.

Cheers,
Stefan