I am shooting downhill skateboarding ranging from 30-60 mph. I'm trying to find a good lens to capture focused sharp stills of the skaters with blurred backgrounds. I have a Nikon D3200. I only have the kit lens and am not getting good results — not a surprise. I was thinking of trying the Nikkor 35mm F/1.8 due to the high speed F/1.8. Thoughts?
Normally the wider aperture of a faster lens allows you to use shorter shutter speeds to 'freeze' motion. But when you are trying to do panning shots to show the skateboarders moving through their surroundings you need to use longer shutter speeds than what you would use to freeze the entire scene.
From a hardware perspective what would probably be most helpful is a lens with a Vibration Reduction panning mode. This allows the VR to steady the lens in terms of, for instance, vertical motion as you pan the camera horizontally. Several Nikon lenses, particularly those in the telephoto range, have this feature.
As is the case with most good photos, the largest factor in a good panning shot is the skill and experience of the photographer. It takes a lot of practice to learn what works and what doesn't. It is a lot like trying to learn to hit a curve ball, you can discuss the theory all you want but you don't really find out who can learn to do it and who can't until you get on the baseball diamond.
Two primary factors that will increase your chances of getting a good pan are focal length and shooting position. First, you need to place yourself in a position so that your subject is the same distance from you as they move from left to right, right to left, top to bottom, etc. The best way to accomplish this is to shoot from a position that is 90° with respect to the direction your subject is traveling. Second, you need to use the longest focal length lens you can that will allow you to compose the shot you want. This allows you to move further back from the subject. The greater shooting distance allows the lens to compress the differences in distance between the arc of your camera's point of focus as you pan and the line that your subject is moving.
For more on panning technique, see What equipment and settings do I use for panning shots of moving objects?