Once in awhile you stumble on a product, where it is clear, that the manufacturer just went all the friggin way, making all the right choices in all the right places. Such a product puts a smile on your face every time you use it, and I just feel like giving a big hi-five to the manufacturer. In this case it is the japanese lens and camera company, Sigma, for making the Sigma 150-600mm f5-6.3 DG OS HSM Sport.
I don´t know the inside story, of how Sigma stepped up from making a range of average to decent, good value-for-money lenses, to making lenses that are a complete no-brainer to choose, even over Canon L lenses. (I am a Canon user.) But fact is, that it happened. I realized that, when I bought the Sigma 50mm f/1.4 ART. (An awesome lens that Canon simply does not have a match for, yet. People would still buy it at twice the price.)
So, given that *something* very good had happened to the Sigma company, I was very intrigued by the launch of the 150-600 Sport.
When I was invited to go to Cape Town and shoot kiteboarding for the company Woo, I went with my gut feeling, and bought the 150-600 Sport a few days before take-off. I had been shooting kiteboarding and surfing in Cape Town before: First time with a Canon 400mm f/2.8 (with 1.4x TC). Second time with only 200mm f/2.8 (with 2x TC) as the longest. I knew if the 150-600 Sport was as sharp as tests were showing, it would be killer. I was also contemplating the new version of Canon 100-400, but it was just not available yet, which made the choice dead easy.
These are some of my thoughts about using the Sigma 150-600mm Sport: (Note: I am not going to be scientific at all, nor post specs and pictures of the lens. You can easily find that elsewhere.)

Build:
Yes, it is not exactly lightweight, but there is no doubt in my mind, that there is a good reason for that. The build quality is outstanding as is the design. Sturdy, smooth operating and beautiful. I will not go into all details, but a few highlights:
The tripod collar rotates with the smoothest feel ever, and clicks gently into place at 90 degrees. (Canon designers: Take notes. 🙂 )
The zoom can easily be locked at marked intervals.
The lens shade is soooo well built, with a thick rubberized lip, because that is what you want, when you let your camera/lens stand in vertical position on the ground.

In use:
One thing that is very important to me is: I can use it handheld. Not for a whole day, but for an hour or so: no problem. (I am not particularly strong.)
The zoom can be operated by turning the zoom ring or by just pushing or pulling the outer part of the lens. By now, I never touch the zoom ring. Ever. Why? Because push and pull just works perfectly and intuitively for me. It gets me to where I want to be instantly, and ergonomicly it just works too. I love it.
The tripod collar with its 90 degree clicks: Ahh. So sweet.

Focusing:
I am happy. Fast enough for anything I could throw at it.

Image quality:
Yes baby, yes. I have been shooting with a Canon 5d MkIII, and I could not be happier. I have used it primarily wide open, and I never felt the urge to stop down because of lack of sharpness. (Not the case when I shot with Canon 400mm 2.8 with 1.4 TC. )
Contrast and colour: Great. Nothing to report, really.
Vignetting: Vignetting is noticeable, but I think Sigma did the exact right compromise here. When building a big zoom lens like this, there are choices to be made, in order to not make the lens ridiculously big and heavy, nor exeedingly expensive. The vignetting is precisely the *flaw* I can live with. Correcting it in Lightroom is piece of cake, and the consequences are very slim.
The proof is in the pudding as they say, so take a look at some of my shots.