Every new Nikon seems to be afflicted by a number of maladies, either real or perceived. With the D200, it was highlight banding, very real. With the D80, it was the hot matrix meter, gain very real. The D7000 had it's issues with focus inconsistency, and that was partly real and partly perceived. And then we have the banding issue with the D7100...
You can find chatter about it in images like this on this thread:
|DPR memeber: zofo75|
First, what is banding? It's pattern noise caused by the circuitry that reads the data off of the sensor. Because data is read off in rows and columns, the noise that gets induced tends to form patterns that we perceive as as lines. For the most part, if you expose properly, you won't see it, except maybe in the deep shadows.
Where it becomes an issue is if you abuse your exposure by deliberately underexposing and trying to raise the exposure in post processing. Most of the egregious examples that you find on the forums are of way under exposed images that have been pushed in post, much more than would be reasonable in normal shooting. However, roughly 3 EV seems to be the tolerance before banding starts appearing, and it can even show up if your images have areas of deep blacks. Ironically, if you mostly shoot JPEG, you might be better off, as the blacks get clipped compared to processing a RAW file, and that's where the banding problem usually is.
It's not a problem if you aren't an exposure-bender. At higher ISO, the grain of the noise in deep shadows looks even and natural, but if you look closer, the pattern of grain is less random than what you would expect. This is the beginning of banding; if you push the shadows at high ISO, you will eventually get it full blown.
The practical aspect of this is that the the D7100 isn't an "ISO-less" camera in the way that the D7000 was. The Sony 16mp sensor in the D7000 and the D5100 has exceptionally low read noise, maybe the lowest of all of the sensors out on the market today, DX or FX. The Toshiba 24mp sensor in the D7100 and the D5200 is no slouch, but you can no longer abuse the files in the way that you could with the D7000. In other words, you still need to do what you should have been doing all along: getting as optimal an exposure that you can at the time of shooting.