If you ask me, just based on the info you are giving me, you must be shooting in AUTO.
When you say "decently-lit", that tells me that it is still dark in terms of the way cameras SEE, and especially
through a lens like the two extras you got, which I believe are both f/4-5.6 max aperture lenses.
You would not describe OUTSIDE as decently lit, you'd say it was sunny or shady. Indoors, decently lit sounds
like a room with some lamps on. To a camera, this is not decently lit unless you have a f/1.8 or faster on the camera.
A 1.8 lens lets in OVER 4 TIMES more light wide open than a f/4 lens. Bearing in mind too that the f/4 lens never really
looks that good wide open, so it might as well be a 5.6 lens if you are looking for a sharp photo. SO outside at the zoo,
in the park, etc, where there is rarely a lack of light, these lenses and cameras shine. They struggle as soon as
they come indoors. I take it that your 50mm f/1.8 does not give you the shot you need at the ballet gig? SO you are
likely shooting the 55-200 at this thing? When you are zoomed in to the stage, likely 200mm setting, the 'brain'
in the camera get's awfully upset at the lack of light it is getting out of the lens at 200mm. So even if it SNIFFS
low light, it sloshes ISO out of a bucket into a shot glass. It over-reacts because it CAN. Auto ISO is like the
US govt. It can get all the money it needs to fix problems without thinking about them or fixing the underlying rot
simply by throwing money at the issue. If it works for the people, what the hell, its the people's money anyway.
And just like the US govt approach is wasteful, so is the autoISO setting, and for that matter, the AUTO green
camera setting. It could care less what it takes from you to give you what it thinks you want. And it's masters
back at NIKON want you to get a well-exposed photo in any condition, and the most effective way to give it to
you is with ISO, crank up the gain and the masses won't complain. So while I believe you when you say that no one
on the web seems to know what is causing it, I KNOW what is causing it, lol.
When I got my first NIKON, I bought two or three of the cheapest lenses I could find that fit my needs.
We both have the same lenses, lol. And I use em all, make no mistake. But when I go to a club to shoot
Vanessa or the Midtown Violets, I KNOW not to even pack em. The only good they will do me in a bar is as
ammo when I run out of beer bottles to throw. They certainly won't get a SHOT. Indoors, the fast 50 can
save you. But it will always be 50mm (75mm on your D7000). I doubt that's enough to reach the stage.
Your decision to make is how much is it worth to you to be able to shoot these events? A 55-200mm 4-5.6 lens
is not going to get it. You can get a shot, which is what a kid will want, but to be proud of the result as a photographer,
you will not be satisfied until you get some faster lenses, or rather, a faster lens for that job. Here is a FINE LENS
for your camera and for that need.
http://www.adorama.com/US%20%20%20%20634298.html
This lens is f/4 at 200mm. Which means that it is gathering 4 times more light than your 55-200 at 200mm.
And in case you didn't catch it, it costs less, too. This lens is magnificent when used properly, and yes,
it IS MANUAL everything.
It is easy to spend 2-300 bucks on the wrong lenses when you really need to take that money and spend it
on one lens. Or two. Its like Cuban cigars. My cigar budget bought twice as much once I realized that the
best was usually cheaper. It took courage to make it work, I had to order something I shouldn't to get
the benefits I wanted. Same with Manual Focus lenses. It takes more work, but if you want to do the job right
AND SAVE MONEY, sometimes you have to compromise. That 200mm lens I linked you to costs half as much as
a new Nikkor lens that performs half as well or less.
I REALLY would like to see you at 180mm f/2.8 ED for two more times as much light. But as you will see,
that comes at a price.
http://www.bhphotovideo.com/c/produc..._f_2_8_ed.html
Ouch. But I think I got mine for $180, so it pays to look. But make sure someone doesn't try to say its a ED
model but it DOESN'T say ED on the side of the lens. LOTS of people on Ebay have those kinds of deals up now.
Without the ED glass, you're better off with the 200 f/4. FOUR TIMES more light coming in than your 55-200 zoomed in.