This adapter adds only 2mm, and does not require set screw for 1.25" eyepiece in a 2" focuser draw tube.
If you use this, can you please share your practical experience?
I have a 2" filter wheel with my Z10 Dobsonian, and after raising the mirror by some 20mm and adding a GSO Coma Corrector, the 2" eyepiece focal plane is at 78mm separation distance from the top lens of GSO CC, and I have enough back focus, even when I use a 10mm long/high regular 2" to 1.25" eyepiece adapter, for Delos 12mm (offset 6.35mm) and ES68 24mm (offset 3mm). My only 2" eyepiece is ES82 30mm, and it works at the 78mm separation, since the offset is 0mm.
However, the view through my LVW65 17mm is no good. I suspect with a 0mm offset, the eyepiece field stop is 88mm from the top lens of the GSO CC, which is beyond the unofficial recommended range of 65-85mm.
I am looking for another 2" to 1.25" adapter that adds as little as possible to the optical length. I have considered negative profile adapters, but they require set screws. The Howie Glatter Parallizer adds 0mm, which seems perfect until I started planning to parfocalize the 1.25" eyepieces, within the limitation imposed by the GSO CC. I have 5mm thick 1.25" parfocal rings. Adding no parfocal ring to the LVW 17 would not work if I add a ring to the ES 24mm since the difference is only 3mm while the ring is 5mm thick. To achieve this, I have to add a parfocal ring to the LVW 17mm as well as the ES 24mm. The 1.25" eyepieces will therefore be 5mm further than the ES82 30mm 2" eyepiece.
So my thinking is with a 2" increase in optical length, the variation in focal plane is at 2mm maximum, using the Hutech, and less than the 5mm with the Parallizer. The maximum variability in eyepiece to coma corrector top lens is minimized at 2mm with the Hutech.
This is all theoretical, and I would like to hear your practical experience with the Hutech.