[Brightcolours]

Actually, here you go

 



 

Screen capture I had made from LR some while ago. On the left is a Sigma 17-70 at 70mm. On the right is the Beercan at 70mm. Shot from the same spot, quite close to the minimum focus distance. Beercan image EXIF is being tagged at 75mm at the wide end btw, even though it's sold as a 70-210mm lens. 

 

Also, FOV will not always be narrower towards MFD. Nikon's old 70-200/2.8 that is being discussed here gets significantly wider at MFD. Even  you said so:

Read what I wrote  :

"Do you realize that when one does not change focal length, FOV always will narrow towards MFD?"

 

With "one" I meant a lens. So when one lens does not change focal length. So, if the focal length DOES NOT CHANGE. This then means that the focal length of that Nikkor VR II does indeed change a lot, it gets a lot shorter. 

If it would only get a little shorter or would not change, FOV would narrow towards MFD.

 

Is it clear to you now?  B) 

 

Not sure what above image is supposed to show. I do know that with the Sigma 18-50mm f2.8 EX DG I had it shortened focal length towards MFD to such an extent that you saw the FOV get more wide towards MFD. My guess is that the Sigma 17-70mm does the same (look through the view finder when going through the focus range, and it will be clear immediately).

 

To make things more graphic:

[ATTACHMENT NOT FOUND]

 

On top you see the FOV change towards MFD of my Canon EF 70-200mm f4 L USM at 200mm setting. You see it get more narrow at MFD compared to infinity. This means that its focal length loss is quite minor.

On the bottom my then Sigma 18-50mm EX DG at 50mm. You see a very severe FOV widening towards MFD, which means a quite severe focal length loss.

 

You see what my guess is now, about your 17-70mm?