The focal length does not change and is 35mm. Even though many will claim otherwise. But on the APS-C camera you will get the same angle of view as with a 52mm lens on a full-frame camera. It doesn't matter whether the lens is designed for APS-C or full-frame. You could also use a full-frame lens with 35mm on an APS-C and get the same image.
Hello Robert. The swlber lens will fit a Nikon D850, but it is built for a smaller DX format sensor. So you will have an unsightly dark edge with your full format. You may be able to switch to DX in the camera's menu, but then you will lose pixels.
I would recommend that you buy a lens for full format. But this lens will fit your camera mechanically.
This one fits quite well. as already answered in the Nikon AF-S DX 55-200mm question.
The 50mm 1.8 would also be recommended. Just check whether the angle fits. whether it is not too wide-angled.