Kevin_A Is that the Kase Bahtinov mask?
No. I have the Kase; it produces bright spikes, but like all single Bahtinov grill-pattern masks, do not work with very wide angle lenses.
A skewed ray bundle in a wide angle lens would for example miss one or more of the Bahtinov sections, and you end up with missing spikes. For a star near to the corner of the 40mm lens, I would sometimes see one pair of spikes only, sometimes two pairs only with the regular masks,
The Hungianian one is quite smart and consist of a mosaic of smaller Bahtinov masks, so every ray bundle will see all three of the Bahtinov grill patterns.
The resolution of the thing (you need a magnifier to see the grill patterns) is so high, the spikes are very bright, too. Plus the size of the spikes is humongous. It is not laser etched glass or plastic (like the Kase), but is done using photographic negatives. The negative is then sandwiched between 100mm x 100mm plexiglass to protect it.
https://focusonstars.com
This mask does not work with longer lenses, so I also bought his "Tele" version. Same technique, using very fine lines, so very strong spikes even though it is a single Bahtinov grill.
They are a little clumsy since they need the 100mm square filter adapters. But at least the wide one is indispensable. When done with backfocus adjustments though, you can probably do without the wide mask, since all you need is to focus on a central star. But I find it extremely useful when looking for backfocus. When I am done with backfocus on the Sigma 40mm, I will probably go back the the regular 82mm Kase mask since it is much less cumbersome.
Even the "standard" etched glass/plexiglass lens-threaded Bahtinov masks like the Kase have higher resolution than the cutout metal and 3D printed ones, or the stupid cutout plastic ones in the William Optics lens hood (those cheap junk are next to useless). You will get a culture shock when you start using them.
The Kase one also produces crisp spikes. But lower resolution masks than the Gabor one, so the spikes are not as long and as bright as the Gabor. Also, the Gabor wide mask is still the only one I found that works at the corners of wide angle lenses.
I have since also found a place that makes very large "glass" Bahtinov masks, so I got a 95mm one (mounting on a Thousand Oaks aluminium cell that I cut out the mylar film :-) for my FSQ-85. That makes brighter spikes on the Baby-Q than the standard 82mm and 77mm glass/plexiglass masks.
https://mavenfilters.com/product/starry-focus-filter/
What I have done with the 82mm masks and filters is to mount them on the Kase magnetic rings. This lets me simply plop the masks and filters in and out without trying to thread them.
https://www.amazon.com/dp/B0CH9FNNZB?psc=1&ref=ppx_yo2ov_dt_b_product_details
One ring from the pair is screwed onto the camera lens, and the 82mm Bahtinov masks are screw onto the other of the ring pair. I have also mounted these Kase rings on the 100mm x 100mm filter holders. Once of the magnetic sides is mounted on the lens, you can also buy the filter end alone, without having to buy a pair of them:
https://www.amazon.com/gp/product/B0CG2PH8XX
They are really life savers in the dark. The shock value when seeing bright spikes all over the FOV is almost worth the value alone :-).
Oh, the spikes are as blurry as the stars when it is out of focus. But when these high resolution masks are in focus, the central star in the Bahtinov diffraction is a very small pinpoint, making it easy to judge if the central spike is centered. I have been centering them by skewing my iPad screen so I can see if the central Bahtinov line crosses the central star. Notice the lack of "hairy" stuff coming from the central star too on the Gabor mask. I will make s magnified version of a bright star to show how clean it is. I should be able to find one from my saved images.
Chen
