As you can imagine, the main difficulty to take these pictures was the weak light. Especially, my Nikor 55-200mm has a small aperture. So even with aperture at max and iso at 1600, my shutter speed was too slow to freeze the movement of the artists. I had to catch them when they were almost motionless.
The background was almost completly black naturally but I pushed it further in photoshop to clean the noise and enhance the lightings and the artists. I love the effect. I will probably use it often.