So here you are. You're standing in the barricade of your local 3000 capacity venue about to take on whatever lighting is coming with the next fast-paced rock band. You enjoy photographing concerts and see how difficult it can be. The band before had next to no lighting up front so you're cranking your ISO to be able to expose for them as much as possible, but even then it isn't doing much. How do you prepare for a band whose lighting may be unpredictable, unknown, or knowingly difficult?
I could give you the "simple answer", but simple isn't in my nature. I'll try to keep it shortish nonetheless.
Your light meter in your camera is designed to handle exposure based upon one of the three modes you may have your camera set to: matrix, center-weighted, or spot metering. I'll break those down real fast if you aren't sure of the differences:
Matrix: This divides the entire frame into different "zones" and then analyzes them individually to come up with the exposure
Center-weighted: Center-weighted gives weight to the overall exposure calculation. So basically the circular area in the middle of the frame averages everything it finds there, giving that calculation a 75% weight in the overall computation for exposure.
Spot: This uses the focusing point you have chosen to calculate exposure.
So as you can see, each metering method is different and can draw different results.
Now just for the sake of discussion, let's say you have your camera on Matrix metering mode. So this is dividing the entire frame and then analyzing and calculating the "best exposure". This isn't going to help you when photographing concerts. If you're like me at all, I make sure to photograph not only individual shots of performers at shows, but I am a fan of my wide angle lens. I like to capture the whole band on stage when possible.
So if I'm shooting wide, not only will my camera by calculating exposure for the front-person who will undoubtedly have more light on them, but it's also exposing for the very bright lights above in the back of the stage, the drummer who is in completely darkness, and so on. Common sense tells you that it's going to give you a good average to use for shows. but it won't.
The simple reason why these meters don't work very well for stuff like concerts is due to how they're designed. They are designed to handle reflected light only. This means the best they can do is guess how much light is actually hitting the subject. That's right, I said they guess. So my question becomes: instead of having the camera do your work for you, why not learn to guess the exposure yourself and be more accurate in the process? You, being a human with human eyes, can see both reflected light and incident light. So you already are two times BETTER than your camera is at judging exposure by design alone. So how do you do that? This is fairly simple.
There's a couple things you can do to get better at judging exposure at concerts. The first thing is to shoot a lot of them! The more you shoot in unpredictable conditions, the better you become at learning to adapt to them quickly and without reliance on your meter.
The second thing you can do is playing the "guessing exposure game" wherever you go. This will get your mind thinking about what to set your shutter, aperture and ISO to every time you're out. It will translate to the concerts you shoot later on.
Thirdly, you can simply go by the "three shots or less" method. Essentially, guess the exposure for your first shot out of the gate on the band you're shooting. Chimp the back of your screen, and guess your adjustments from there. Is it maybe a stop and a half under exposed? Okay so I need to go from ISO 2500 to 5000, and bring the shutter speed down from 1/400 to 1/250th.
You go from there and you'll find what works for you for that show. From there, I personally just ride my shutter speed by "clicks" as the subject gets darker or lighter. Meaning for every 3 clicks I adjust my shutter speed, it's one stop of light. If I think he's stepped out of the main light and it's a good 2 stops of light in difference, I can either pull back 6 clicks on my shutter, or 3 clicks on my shutter and 3 clicks up on my ISO, and so on.
Is it a convoluted way of getting things done? Maybe. Is it more effective than using your camera's meter? I think so. Do I think I can judge exposure better than my camera when photographing concerts? Facts and photographic proof says yes.
So that's a brief explanation of why the light meter is essentially pointless for photographing concerts and unpredictable lighting conditions. I hope this helped and I hope to see a bunch of photographers walking around grocery stores now mumbling camera settings.