Manual Focusing in Live View Mode on Your Nikon D7100 For manual focusing in Live View mode on your Nikon D7100, set the Focus mode selector switch on the front-left side of the camera to M. If you’re using a lens that has a focus method switch, set that switch to M as well. Then turn the lens focusing ring to focus. But note a few quirks: How to use manual lens on Nikon D7100 DSLR Dec 08, 2013Just got in the mail and I was SO exited to try it out. It's a 85mm Nikkor AF f1:1.8 D manual lens. I have a Nikon D7100 . I tried searching on the internet to see if this lens was even compatible and it seems it is. But I have no idea what I'm doing wrong. First I tried it on auto focus, then I changed the camera to manual focus and still nothing.