Originally posted by axl I don't have any of those two but I think other than 70mm they don't have much common. DA70ltd was made as pancake. So small, light, portable, durable and excellent IQ so ideal for trawel and street photography. Sigma 70 is dedicated macro lens. And as such big and heavy (at least when comparing with 70ltd) but again with great IQ and pin sharp. Otherwise, Pentax is 0.5 stop faster, and IMHO that's just about it.
So what sets them apart? What usage they were designed for...
BR
I have both, and both are so different, for normal use the DA 70mm just wins due to size, weight, fast AF. If you need a macro then the 70mm sigma just can't b beat for sharpness, but at normal ranges both have the same iq but the Pentax has better rendering and warmer. BTW the Sigma is a huge Brick! and it's AF is VERY slow.
Different lenses for different uses and I would not replace one with the other.