There have been some questions recently in my mailbox, asking what is needed for concert photography and basically how it's done in practice.
I'd like to tell you what I started out with a couple of years ago.
I had a Nikon D90, which has the D7200 as a successor today, combined with a 50mm 1.8 lens.
That's the gear I started out taking pictures in crappy lit venues.
The aperture of 1.8 really helps and it's reasonably priced as well.
It doesn't matter, if you're on Nikon, Canon, Pentax or even Sony.
Just get one.
The more expensive stuff like the 70-200 2.8 or 24-70 2.8 is nothing you should bother to get - especially if you're just starting out and got some space in front (or on) the stage - you can still do that later.
There is, at the shows I covered, a more or less fixed value for exposure time you can use for orientation. It's 1/100 sec, or faster.
For me 1/100s or faster was neccessary, because bands in rock- and metalgenres are likely to move fast.
Next thing to worry about is the aperture.
To maintain a certain level of sharpness, I tend to start at an aperture of 4.
1.8 is rarely used and only if neccessary - more about that later.
A valueable piece of information is how high you can go on ISO before grain gets too strong.
On my D90 that was 800.
Everything higher made details fade too much and faces barely recognizable.
With most of today's cameras, you can go significantly higher on that.
ISO is also the first thing that gets lowered, if light gets better, just to have some images with less noise.
With a full-frame camera, things get less stressful, but most beginners won't want to invest that much money on a camera.
If the Aperture of f/4, 1/100s of exposure and ISO of 800 aren't enough, I'll open the aperture, first on 2.8 and 1.8, if the first still isn't enough.
If that's still insufficient, I ask the stage lighting-guy to crank the lights higher.
Usually that helps.
Always be nice to the light-guy!
If even that's not enough or there is no light-guy, you need to make tough decisions.
You can crank up your ISO higher and accept the grain or take the risk and slower the exposure and pray for some clean shots, or you use a flash and turn that on a "low" setting, to not flash-kill your images.
If flash usage is prohibited, you could still try a flashlight.
There are cellar/basement venues, where you just got no choice.
Furthermore it's crucial to shoot RAW.
By doing that, you get the chance to rescue some under/overexposed images, which would face deletion in jpeg.
If none of the steps above are any help, you get to a point to realize that you need light to take pictures.
No technical "trick" will provide any loophole out of that basic physical principle.
Not even with a D800, D4 or 5D MkIII.