My biggest (and only one so far) concern is about the reach.
I've read a couple of times that the Siggy is shorter @ 300mm than the canon fixed 3002.8ISII. Those reviews were about the previous model of 120-300 but it ain't supposed to be optically different from the brand new one.
If this was real, the Sigma wouldn't be as interesting as it seems...
Ideally i'd buy it to complement my 70-200 as the 120-300 remains really cheaper than the Canon 300mm and i often need an extra reach that a 300mm (or 420 with 1.4x) would bring me.
Anyone ? Have you ever heard any kind of complaints like this ?
Does anyone could compare the reach of the 120-300 to the 300L ?
"...Siggy is shorter @ 300 than the canon..."
It irritates me when people make confusing statements like this without stating what focus distance they are referring to.
I suspect that focussing at "infinity" ie in practice say 200 to 300 metres and beyond the new Sigma is probably a true 300 lens. However it seems to be the case that at close focus zooms generally loose focal length faster that primes.
The same used to be said of the 100-400L. I once carefully compared image size of a 100-400L @ 400 with the Canon 400/5.6 using same camera focussed on a distant building and guess what - the image size was exactly the same ie my 100-400L was a true 400 at distance.