For those interested in the technicalities of the issue heres a focal plane vignetting plot of an F10 cone through a 26mm aperture ( ie Denkemeir binoviewer ) with a 114 mm pathlength. It shows why a 24mm Panoptics shows vignetting at the edge and not a typical 20mm eyepiece
If you trace the semi-aperture at the fieldstop of Denk 21mm eyepiece ( about 11mm ) the light transmission is about 70% at the edge, which is on the margin of casual detectability for the human eye. A 24mm of 14mm semi-aperture indicates 45 % illumination which will be obviously appear vignetted to the human eye.
There lies the dillema of binoviewers. The long internal pathlength demands a slow F ratio to get acceptaable off axis lighting which means a narrow field of view compared to a true Newtonian binocular. Astronomy like life is full of compromises if you want to take a shortcut
.