This Sigma long telephoto zoom is a cut above your average 70-300 level of performance and construction. It’s a big heavy lens - 1245g - but very well made and finished in my favorite Zen rubberised coating. Performance is excellent. Best at the shorter end up to about 300mm but resullts are still perfectly acceptable at 400mm and full aperture.

I was surprised to find that my old Sigma 400mm f5.6 APO is noticeably better at full aperture but the flexibility of the zoom means that the 135-400mm gets used much more. Certainly the performance of this lens at the long end is much better than a Sigma 70-300 APO Macro II I owned briefly. That lens was truly excellent at 70-135 but faded quickly to not really very good at 300. So if you’re wondering if this (and I’d imagine the Sigma 170-500 released at the same time) is better than the Sigma APO 70-300 the answer is yes, quite a bit better. I know which one I’d buy again.