Upload & Sell: On
well look at it from the other end. the last FW from Nikon and I quote:
"•Support for the AF-S NIKKOR 800mm f/5.6E FL ED VR has been added."
so it looks like the cost of the 800 to work properly on the Nikon bodies, as this was across the board, was a firmware upgrade but just done in the camera body.
we all know that 3rd party makers do not have access to the camera firmware so they do what they need in the tube of glass in the front.
in the end its pretty much equals out and is not so "priceless"
sigma has set limitations on their newer lenses as to what can be controlled by the user on a per lens product basis. all what can be done to/with the 120-300 cannot be also done to the 17-70. you do not need to invest in this operation to use their lenses as is. it is merely an option.