I owned the Canon 135/2-L for a number of years (10 years or so) and felt that it was a fine lens; SMALL for a 135/2! Lighter, smaller, less dense than the Nikkor 135mm f/2-AiS, smaller it felt than the 135 DC Nikkor. My feeling is that with a 135mm lens of high speed, like an f/2, that autofocusing is worth a huge amount. Critical focusing is super important now that we have 20+ megapixel resolution. Manual focus used to be easy on 35mm SLRs, but on d-slrs it is less easy, less sure, more prone to misses. And the Canon 135/2-L is one of Canon's better lenses. The Zeiss is a nice lens, but again--it is a manual focus lens, in an autofocus world. I do not think it is the way to go, I think an AF lens on an AF camera is the better idea.