[Rover]

Might be needed for low-light shooting. But I'm just splitting hairs, because this is, as Fred Miranda has put it (quoting Roger Cicala I guess) "the absolute best SLR lens".

The corners seem fine at f2, and shooting wide open... why would one need extra sharpness in corners?

Anyway... my 55mm f1.2's vignetting is much worse (as is its background bokeh and just about every aberration).

 

The Sigma 35mm f1.4 is not in any way of the level of the Zeiss... The Zeiss is really impressive in what it does. That does not mean no other lens maker can't design an equivalent lens, but that lens then too will come at a high price.