I have a D3200 currently and am very interested in bird photography. I have seen some very good things about the tamron 150-600mm and have made the decision to get it but after some research I am not sure if I need to upgrade to the 7100 first before I get the lens. I was already planning on doing this but it takes me a while to get enough saved considering I am still in college. Does anyone have any experience shooting with the tammy on a 3200?