I don't know if it is a con when using the tc 1.4 III and you just have to live with it when you want the added reach or it is something I am doing wrong. I am using the tc 1.4 with the nikon 200-500mm f5.6 and the same pictures without the tc are sharp and the ones with the tc ALWAYS seem to be soft and little blurry when magnified to 100% in lightroom. Suggestions welcome, never exceed 100 iso?