Today I think one is on the wrong track to conlude, genuine lenses are the best choice. Nikon or Canon or whatever: There are product life cycles, research and development happens every day. Even Nikon can not guarantee that all lenses work best - if you don't believe, check AFMA of a Nikon lens with different distances.
Nikon also has "techncial difficulties" and cannot solve all of them perfectly. They also have a big overhead of administration costs and are far away from most customers, ambassadors or other key persons being an exception.
The 500 your talking about is f/4? and the 600 G2 f/6.3, if I recall correctly? I don't think that's about Nikon and Tamron, it simply is about the limit of f/5.6.
I never said that things are perfect or you need to buy Nikon lenses, otherwise I wouldn't be using the G2 as opposed to the Nikor 200-500mm!
However, you asked me a question which I think that I answered objectively, any manufacturer who designs lenses for his own cameras has a head start advantage......the knowledge of it's own system.
........what goes on with TPMs and reverse engineering is another story and we are seeing plenty of great results from those too.
......but Nikon knows 100% intimately their AF system and doesn't have to compromise things for other mounts........so if they can't get things right.........they only have themselves to blame!
The 600mm and 500mm I was talking about was just about zooming on the same lens, the G2!......
..........a light gathering issue.
Well dave, I work in a machine manufactory. All I can say is that most designeres here are too young to know the machines we made 10, 20, 40 years ago. All grinding machines. The engineers simply do not have the industrial-historic background - so sometimes they make mistakes we already made a decade ago.
I do not believe that the designers of a D90 knew which lenses Nikon would produce a decade after the camera introduction, same with 20 year old lenses. We don't see incompatibilities inside, just as a result and then it's already a problem. Or the lenses which were made for a D3, 12 MP, need to resolve and AF with these days nearly 4× higher resolution.
I don't know what my employer wll produce in ten years from today, so how could I adjust myself today? That's what I meant with reverse engineering - Sigma or Tamron will analyse both brands and probably know a lot more about Nikon AF than Canon does or vice versa. There's no need to compromise things for other mounts.
Sigma lenses are not pretending to be Nikon lenses, but all identify themselves with the proper FL/f numbers
Also, in EXIF you will see their names / numbers.
The USB-dock is approximately working the same proportion numbers of AFMA (AutoFocus MicroAdjustments). Meaning: It doesn't matter much if you correct the lens only in-camera or use the dock to apply the same correction (and not on camera). It's also possible to correct the lens for all distances and focal lengths (and set in-camera AFMA to 0) and then put it to the next body and just correct the whole system, if necessary.
As well as it's possible to do corrections bigger than 20, because both values add. -15 + -12 = -27
The dock is without a doubt, a blessing!
