When the fashion show started, they turned off all the lights except one beam which follows the models. It was very dark and my lense was long. Since I did not want to use flash, I had to set the iso to 3200 occasionally to keep shutter speed fast than 1/100. After some testing, I managed to find the right parameters for exposure and the pictures turned out just like these. All I did under PS was to enhance the contrast a little bit to knock out the already-dark background.