I believe the Korean manufacturer who makes Orion's nebula filters cuts the threads in a slightly non-standard way because I've owned several Orion filters and they've all been somewhat incompatible with the threads in other items--especially eyepieces. And I've read numerous posts on many on-line forums where other people have experienced the same thing.However, they've all engaged between 1 and 2 threads and filters are so light, that's sufficient to hold them on. And you can "chase" the threads by threading them further in and backing them out and then repeating the process until the filter threads in far enough you're comfortable with it. As for the fit in eyepieces, well, eyepieces vary a lot. The threads are one of the sloppiest-machined parts of astronomy. Barrels vary in outside diameter and even vary in roundness. It's just the way it is. I've seen eyepieces into which no filter would thread because the ID of the eyepiece was too small, and I've seen eyepieces where the ID was so oversized every filter could be pushed in and pulled out without any threads engaging at all. So pick what you pick because you want that filter and don't worry about the fit. It'll work, one way or another.. Orion or Lumicon 2 H-Beta filter - posted in Eyepieces: I have been thinking about getting a H-Beta filter and trying to see the Horsehead now that I have a 14" scope. I have always been happy with my Orion products but I have not done much research on filters until recently. Im looking at 2" now thanks to Don reminding me that they screw into . Lumicon 2" Hydrogen Beta (H-Beta) Filter. Also known as the Horsehead Nebula filter, the Lumicon 2" Hydrogen-Beta Filter isolates only the hydrogen-beta line of the spectrum (486 nm) in a narrow pass-band just 9 nm wide, providing maximum contrast..