Shooting at concerts and gigs in low light is one of the trickiest environments to take photographs in.
You often find that the light changes so quickly it is almost impossible to get the right exposure before the lights changes moreover timing the moment when you press the shutter with the correct exposure often leaves badly under or over exposed photographs. Shooting at concerts and gigs in low light can be very fulfilling but you need to know how to set up your equipment to get the best from the situation.
I am often asked to shoot concerts for the national press and I can give you some tips on where to start.
First of all you need to gauge the average light by taking some test exposures, once determined lets say 1/125s at f5.6 with an ISO of 1600 you are ready to go.A lot of this is about experience, look at the lighting and gauge how far above or below the basic exposure you have is actually falling on the subject. A spot ligt on the singer could be +2 stops of exposure so as you aer shooting make adjustments. Depending on how your camera is set up (I woudld suggest APERTURE PRIORTY) you now close down the aperture 2 stops from f5.6 to around f11. In another scenario the stage may only be lit with a single low power flood, in this case from your basic exposure aperture of f5.6 you woudl open up the lens to f2.8 allowing more light on to the sensor.Now you can see why the basic setting is around f5.6 as it means without taking the camera from your eye adn missing the shot you can vary the exposure over +/- 4 stops.Sometimes it is a case of gettign the shot adn not worrying too much about exposure so assuming you ahve a good basic exposure your image can then be push or pulled further in post production, I use Adobe Lightroom, whihc allows another +/-2 stops fo adjustment.As you can see once an average exposure is set adn you make adjustment sin shooting coupled with post production you ahve an exposure range of around +/- 8 stops, more than enough to get great concert and gigs in low light photographs.