LensRentals' Roger Cicala has published an interesting comparison of the Zeiss ZE 135mm F2 APO-Sonnar and the Canon EF 135mm f/2L USM lens, with both optics mounted on a Canon EOS 5D Mark II. While you'd expect nothing less than excellent results from the Zeiss optic, just what advantages can the heavier and much more expensive lens offer compared to Canon's well-regarded prime lens?