it's not the fastest lens out there, but for daylight birding and wildlife, it has promise. it weighs 40.9oz, significantly less weight than the non-sports 150-600 at 68oz. here's what sigma has to say: Full Frame Lens with APS-C compatibility Compact size meets strong image quality https://www.sigmaphoto.com/lenses/telephoto-lenses/100-400mm-f5-63-dg-os-hsm-c
I had checked the performance, I mean the IQ of this lens were ever I could, and it seems to be a very good lens. Not as good as Canon 100-400mm EF L IS mark2, but very, very close. At some focal lens, no difference at all. So, regarding the price, a very strong competitor.
