I have done a fair amount of ballroom dancing photography. I started out with the camera set on automatic and used just the camera's flash and shot only when dancers were fairly close. I used a 17 - 200 lens (Canon) and it gave me the range I needed for close and intermediate distance. The shots were spectacular! The key is to shoot when the lady's dress or costume is flaring out. Later on as I became more interested in manual settings I used an external flash with greater range and with a 200mm I could cover most of the dance floor. Most dance competitions won't bother you if you are just shooting a particular person and you can use flash. Don't ask….just do it and no one will bother you. If you ask they will tell you that an official photographer is the only one with the competition's permission to shoot. They are simply protecting the official photographer's right to sell the photos. However, you can shoot better photos of a person because you are motivated to catch her in the right move.