yabokkie: not sure Sony is able to make any good lenses. using of a brand of someone else who hasn't made any good lenses for dozens of years since lost market to Japanese makers in 1960-1970s is a proof that the quality of these lenses are low.
Zeiss brand = low quality. G lenses, not sure.
You've obviously never used a Zeiss lens. And i guess you missed the part where the Sony 70-400/4-5.6 G was rated best in class of any system.
Zeiss is a world famous lens maker. They make glass for Canon & Nikon too... just an FYI. They also make optics for medical and industrial applications, and are used almost exclusively for neurosurgery microscopes. You better hope that if you need brain surgery, those low quality zeiss lenses are there to help your doctor fix you up. :)