Using the Hyperion zoom in my refractor scopes posed no in-focus problems (more so on my SCT & Mak), like with the William Optics Megrez 102ED scope shown below:
Hyperion zoom on a WO Megrez 102ED refractor
Or with my Antares 6" refractor:
Hyperion zoom on the Antares 1529 152mm refractor
Or the Orion ST80:
Top: Orion ST80; Bottom: William Optics 66mm petzval
But the WO 66 ED refractor shown above (my RDS - Rapid Deployment Scope for quick looks & favorite for lunar photos w/the Hyperion zoom) was a bit finicky and wouldn't come to focus with the zoom using an OPT diagonal (which came with the scope when I purchased it used in immaculate condition in its WO soft-case and a WO 188 tripod all for $290). It required more in-focus racking.
The good thing was that the OPT 2" diagonal's EP-side lip can be unscrewed:
OPT 99% dielectric 2" diagonal lip (EP side w/Hyperion 21mm)
So I had a substiture aluminum low-profile lip custom machined to screw-in to the diagonal, replacing the original EP-lip, and that solved the problem by moving the light path closer to the EP; the Hyperion zoom now works glitch-free focusing on the WO66mm . There are also off-the-shelf low profile adapters available as have been discussed in other threads on here.
2" OPT diagonal w/custom made EP-side upper lip
Hyperion zoom on a custom-made 2" low-profile adapter on the WO66mm Zenithstar refractor
The WO66ED/BHzoom duo is my favorite afocal astrophotography gear for Moon shots.