Quote Originally Posted by waileong
It's got one more lens element. That's a design difference that must contribute to a better image
More lens elements don't necessarily deliver better image quality. Leica M lenses are a good example of this: they tend to have fewer elements than competing lenses yet deliver very high image quality.

You can compare the technical image quality of these lenses in the following PDFs from Zeiss:

The CF lens
The CB lens

The CF does seem marginally sharper with marginally less distortion. I doubt you'd notice the difference in normal use, although you might notice a contrast difference in favour of the CB.