Just went to play around with my new D5100 a bit. I have been using the old D50 for so long. In no certain order... I present to you, boring pictures.

 

are you shooting raw? The pics look good apart from the while balance being off and that's a really simple fix if you shoot raw.

 

Thats a simple fix regardless of format.

They looks pretty good. Its not the best lighting but thats not your fault, you did a pretty good job dealing wth it.
You do have a little bit of a crookedness problem in a few of them though.

 

Not really a white balance issue, it's just the color of the lighting. The lighting throughout the museum varies from pure white, to warm. The first picture of the track, the white balance is off a bit. Crooked, maybe. Mostly intentional, except for maybe one of two of them. Mostly I was just getting shots to compare to my D50's terrible "high" ISO performance. My D50 couldn't shoot anything over 400 without becoming really grainy in the shadows. This camera is about to shoot as clean or cleaner at 800 ISO as my old camera could shoot at it's lowest of 200, and has perfectly usable shots at ISO 1600 and 3200. I just don't like grainy images.

 

the color of the lighting is exactly the reason for the white balance being off. In raw you can just pick the WB tool, click on a white or gray surface and it snaps directly to a "mostly" perfect white balance raw makes everything simple, and even noise corrections. If not, then noise ninja is good too.

 

But again, the white balance is set as to make the lighting look like it does in real life, which is redish. If I wanted a more white light, I could make it that way, but I didn't.

 

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My D50 in the last year has also developed a lot of hot pixels.