What were your disappointments with IQ? The photos you posted seem okay, although the duck seems a little soft. Was the tracking issue the same, regardless as to the mode used?
All the pics I made of ducks are a bit soft, you ar right there.
Regarding the AF, I used the AF-C (51 points AF) to track the planes in flight and many of the pics are blured. I don't have that problem with my 80-200ED which is a slow lens.
It could be the OS modes as most of the pics were made with the OS1 and not the panning OS2. However, even in that last case, pics are not good. It seems to me that when the OS mode starts (it does take some time), the AF somehow stops tracking.
However, I will give the lens a new try as soon as the weather permits.
these websized images look fine to me. Even the duck. well you could use a tad more sharpening there maybe. care to share a few larger images, 100% crops maybe?
the first two crops are just excellent for a consumer grade lens. The third one could be a focus issue but is not that bad. Which aperture did you use ? because I have used the 80-400OS (I still own one) and the 80-400VR, and those lenses need to be closed down a bit to give the best pictures... (f8-f11 is the optimal zone, using them fully open @400mm is not recommended)
I tried both the 120-400 OS and the 150-500 OS. Both of these exhibited front focus on the short end and back focus on the long end. It was too extreme to dial out with my D700's AF Fine Tune so I sent them both back.
I did get the 150-500 OS replaced and the second copy had only minor back focusing issues that I could dial out in camera. So far this lens has been great for backyard hummer shots. At 500mm it's best at about f/10, but even wide open (f/6.3) it's not bad.
NIKON D700, Sigma 150.0-500.0 OS f/5.0-6.3 | 500 mm | 1/320 sec at f / 6.3 | ISO 800 | SB-900
