Sigma 24-70mm f/2.8 DG OS Lens for Canon

First and foremost this is not a 3,000.00 dollar lens. I do not expect it to have the same exact performance as a high priced Nikkor lens etc. I fully understood the aperture limitations on the wide end. If I had wanted or needed a 2.8 wide range telephoto lens I would have hocked a kidney...sold some blood and one of my children for one. However I did not and so I accept what a lens at this price can and should do. Many people have reviewed this lens so to, yet again, give my two cents worth mostly would be much repetition. I will just hit some points. This lens has the potential to be nice and sharp. Seems many copies including mine have a slight front/rear focus error. I easily fixed this in the D750 AF adjustment...took -3 to nail the 400mm length nice and sharp. Long term fix and to insure spot on at various lengths and apertures I got the USB dock for the lens. It is not expensive and I got mine used...get one. The max potential seems to be with the dock if you need to fine tune the AF to the anal retentive level. The auto focus works fine on my D750. Works as expected...almost never hunts or missed focus and when it does it has mostly been do to the scene or using the incorrect AF metering for the shot. But this was rare. Again its not a 3 grand lens. The OS works fine...seems to add a few stops but then again at 400mm handheld there is limitations to any OS if you want tack sharp especially cropped. Put it on a tripod....simple. The lens is dark yes...but that is obvious...it is clearly stated the max aperture at 400m. If this won't work drop a kidney and a liver on the black market and get a 2.8 lens. Personally I value my kidney and liver and can't afford that so I learn to shoot with it. It does fairly well in moderate light....crank up ISO a bit and a tripod I have no issues. Handheld at f11 or smaller in anything other than sunlight well who's not performing? The lens or the person behind the camera..? The ability to set the C1 and C2 settings via the dock is nice. Helps in different situations to have a quick ability to change OS or AF priority etc. Overall its a fine lens at the price....not perfect but again at this price I do not have any complaints. if I had spent several grand and up then I could talk about a few but I spent under $800 so...keep it in perspective. Last there are always bad or defective copies....happens to all manufacturers even your favorite manufacturer...I have had bad copies of cameras etc from several top brands...it happens. Sometimes it may just not be your cup of tea....if so...drink coffee and be happy.