Auto mode will probably pick too slow of a shutter speed. I know that some people like to use aperture priority, but I prefer to use shutter priority so that I know that I have a shutter speed fast enough to stop motion. There is no point in having a properly exposed image if it is a blurry mess.
With the 50mm lens on your camera, you probably want to be at least 6 feet away from the subject.
I don't use a Nikon camera, but these are the settings that I typically use and would suggest.
- ISO 1600
- Shutter priority: 1/100s - 1/200s. Try for 1/200, but that depends on how much light is available.
- In shutter priority, the aperture will be selected automatically for the given shutter speed. If there is enough light that the camera picks a smaller aperture (larger f number), all the better in my opinion. If there isn't much light, the camera is going to pick 1.8 anyway.
- Spot metering, with negative exposure compensation to correct the metered exposure. The camera's meter reading is probably going to be wrong, so you will need to compensate with exposure compensation.
Here is the most important point. After you take a picture at the show, look at the histogram to check the exposure and adjust your settings according. The settings that you would be adjusting are exposure compensation and shutter speed. Then take another shot and check the histogram again. Repeat until you get a correct exposure.
- Manually select the focus point so that the focus point is over the performer's eye. Do not focus and recompose, since you will be working with thin depth of field.
- White balance: auto.
- Shoot in raw + jpeg for optimal post processing.
- Single shot. Continue shooting just means you get a whole bunch of similar shots.