Right now. I can't detect any
fringe of any color in a binoviewer when used in an f/8 apo scope.

What Binoviewer are you using? Does it have a built-in 3x Barlow? If it does
not have this Barlow, then it will disperse the light slightly - well known law
of optics. Whether you can see it or not depends on your local observing
conditions and how well your eyes respond to the visual spectrum. Some people
cannot see color fringing, even in short tube achromats. For other people, the
same scope will show screaming purple color fringing.

Roland Christen