My brother is performing tomorrow in a musical as part of a week's summer camp thing.

I wanted to take my camera along to take some photos but I'm not sure how to go about it in potentially low light with a fair bit of movement and no flash allowed.

I have the choice of 3 lenses...

My stock 18 - 75mm lens.
A 28 - 150 something mm lens (which is my preferred every day lens).
or a telephoto lens (goes up to 300mm).

Any tips or links or advice is welcome.

Thanks

Whichever lens has the widest aperture, for starters.

Don't use a zoom because most of the ones you note will close the aperture the more you zoom in.

Set the ISO at 400 or higher (most modern DSLRs will handle the noise quite well, so 800 is certainly doable).

Ask if you might be allowed a tripod.

I'd say go with the fastest lens, and don't be surprised if you find yourself up at 1600+.
Like Heather says, a tripod will be a great help.
From my limited cat walk experience, I'd suggest asking to see if you can watch a dress rehearsal, and maybe take notes of moments where there's not much movement, hopefully somewhere well lit.
Also, consider taking a small stepladder with you, or stand on a chair. Chances are you'll be stuck at the back, or off to the side.
You'll get a much nicer framing, IMHO, if you can get up more on a level with the cast's eyeline instead of having them looking over or down on you. It's more engaging.

It's hard to say, really, without seeing where you're shooting, but take your fastest lens (my gut's saying the 28-150 will cover it, but I don't know how fast that is), leave your anti-shake thingy on, try to get in for a dress rehearsal and remember not to get stuck down with the audience.

Thanks both!

I've just had a play around and at the largest aperture is f/3.5 at 18mm for the stock lens or f/3.5 at 28mm for the other (although I lose some of the wide angle as it's an EF lens on an EF-S camera).

That makes the bigger lens marginally faster.

Off topic question, how does the physical lens diameter affect the outcome?

The stock EOS450D lens has a 58mm diameter whereas the other one (actually it's the stock EOS3 lens) has a diameter of 72mm.

Thanks again I might take my EOS3 along with me also