I've owned both the CF and the CB.

- The CB is slighty less sharp, but you need good eyes and high-res film to see & appreciate it.

- The CB has visibly more distortion.

- The CB has better colour saturation.

- The CB has a much smoother focusing ring.

- The CB is slightly 'fatter' (more difficult to get to the release button).

Because of the distortion I sold the CB and kept the CF. But the differences are still minimal.