Hi, I'm a newbie in this forum. I have a question regarding my d750. I never had a dslr that has an AF screw and motor on its body until I bought this d750(body only) a few days ago. This morning, i went to a camera shop for lenses and tried one of their 24-70mm and when I pull out my 50mm lens from my d750, I noticed the AF screw is wobbly. Is this normal or should I contact Nikon to get a replacement?