Sometimes you can stand front stage; sometimes you have to stand 20 meters away. One moment you get a lot of light; the next moment you may get only candlelight during an acoustic song. How do you overcome these technical problems? How do you measure the light with these constant changes? How and on what do you focus? Which camera and lens do you need to get optimal results? It all has to do with the quality of your equipment.
To make concert photos in a professional manner, you need at least a reflex camera. Film or digital doesn't matter, though in this book I refer to digital models. Brand doesn't matter, either. Everybody has their own personal preferences in cameras, be they for technical or budget reasons. Most important is that you have a camera with no delay in shutter time. In other words, you want instant recording when you press the button. You will notice that nearly every compact and bridge camera has a delay that always makes you just a little too late.
Lenses
You've got the camera body: now, which lenses? The gold standard among pop music photographers is the 70–200 mm zoom. This lens offers you the range you need to shoot a total or portrait shot from the front of an average height stage. Take a 24–70 mm lens for stage shots, and you're ready. Many photographers also have 300 mm, 400 mm, or even longer lenses. These lenses are often used at big concerts where photographers have to set up next to the sound-mixing desk.