I've had this eyepiece for a while and it's a very good performer, but I was never completely convinced about its design. I took it apart today and took some photos (which I've enhanced to show its internal structure. I've also attached a small portion of the C J R Lord eyepiece chart that shows the structure of the Bertele design. Unfortunately, I could only remove the field lens, which looks like it consists of two cemented elements, but I can't be sure. The eye lens looks like a plano-convex element, but it's difficult to tell due to the rolled over brass lip that hold it in place.
To my eye, it looks very similar to the Bertele design - more so than any other design. In the side view of the field lens, the curved portion faces the eye lens.
If there are any eyepiece experts out there, could you chime in on this. The B6 eyepiece came with my Monolux-branded Asahi 60/800.